Articoli di riviste: "Femtosecond pules"

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Renard, William, Clément Chan, Antoine Dubrouil, Jérôme Lhermite, Giorgio Santarelli e Romain Royon. "Agile femtosecond synchronizable laser source from a gated CW laser". Laser Physics Letters 19, n. 7 (31 maggio 2022): 075105. http://dx.doi.org/10.1088/1612-202x/ac7133.

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Abstract In this letter we demonstrate agile femtosecond pulse generation with a widely tunable repetition rate (10–100 MHz) from a continuous wave laser diode optically gated by a Mach–Zehnder electro-optic intensity modulator. Initial sub-50 ps pulses are strongly spectral broadened (>5 nm) by self-phase modulation in a polarization maintaining single-mode fiber. A tunable optical pulse train with pulse durations of a few hundred femtoseconds is obtained using a simple fixed grating compressor, thanks to spectral broadening saturation phenomena. The source is easily synchronized with low timing jitter using an external clock signal.

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Ye, Hanyu, Florian Leroy, Lilia Pontagnier, Giorgio Santarelli, Johan Boullet e Eric Cormier. "Non-linear amplification to 200 W of an electro-optic frequency comb with GHz tunable repetition rates". EPJ Web of Conferences 287 (2023): 07025. http://dx.doi.org/10.1051/epjconf/202328707025.

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We present a monolithic Yb-doped fiber laser system delivering 200 W average power of femtosecond pulses at tunable GHz repetition rates. The system is based on a GHz electro-optic (EO) frequency comb operating in the nonlinear regime. The EO comb pulses at 1 µm wavelength are initially pre-compressed to sub-2 ps, amplified to 2.5 W, and finally boosted to 200 W in a newly designed large-mode-area, Yb-doped photonic crystal fiber. Continuously tunable across 1-18 GHz, the picosecond pulses experience nonlinear propagation in the booster amplifier, leading to output pulses compressible down to several hundreds of femtoseconds. To push our system deeper into the nonlinear amplification regime, the pulse repetition rate is further reduced to 2 GHz, enabling significant spectral broadening at 200 W. Characterization reveals sub-200 fs duration after compression. The present EO-comb seeded nonlinear amplification system opens a new route to the development of high-power, tunable GHz-repetition-rate, femtosecond fiber lasers.

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Zeng, Li, Xiaofan Wang, Yifan Liang, Huaiqian Yi, Weiqing Zhang e Xueming Yang. "Chirped-Pulse Amplification in an Echo-Enabled Harmonic-Generation Free-Electron Laser". Applied Sciences 13, n. 18 (14 settembre 2023): 10292. http://dx.doi.org/10.3390/app131810292.

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The field of ultrafast science has experienced significant growth over the last decade, largely attributed to advancements in optical and laser technologies such as chirped-pulse amplification and high-harmonic generation. The distinctive characteristics of intense ultrafast free-electron lasers (FELs) have introduced novel prospects for investigating molecular dynamics, as well as providing an opportunity to gain deeper insights into nonlinear processes in materials. Therefore, high-power ultrafast FELs can be widely used for both fundamental research and practical applications. This study presents a novel approach for producing high-power femtosecond FEL pulses, utilizing chirped-pulse amplification in echo-enabled harmonic generation. Chirped seed pulses are employed to induce frequency-chirped energy modulation in the electron beam. The generated FEL pulse, which inherits the chirped frequency, can be compressed through the gratings in the off-plane mount geometry to provide ultraintense ultrafast pulses. The numerical modeling results indicate that peak power exceeding 20 GW and a pulse duration in the order of several femtoseconds can be achieved.

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Saha, Asit. "Bifurcation analysis of the propagation of femtosecond pulses for the Triki-Biswas equation in monomode optical fibers". International Journal of Modern Physics B 33, n. 29 (20 novembre 2019): 1950346. http://dx.doi.org/10.1142/s0217979219503466.

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Bifurcation analysis of the propagation of femtosecond pulses for the Triki–Biswas (TB) equation in monomode optical fibers is reported for the first time. Bifurcation of phase plots of the dynamical system is dispensed using phase plane analysis through symbolic computation. It is observed that the TB equation supports femtosecond solitary pulse, periodic pulse, superperiodic pulse, kink and anti-kink pulses, which are presented through time series plot numerically. Analytical forms of the femtosecond solitary pulses are obtained. This contribution may be applicable to interpret the dynamical behavior of various femtosecond pulses in monomode optical fibers beyond the Kerr limit.

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Zhu, Chang Jun, Jun Fang He, Xue Jun Zhai, Bing Xue e Chong Hui Zhang. "Two Synchronized Operating Modes of Femtosecond and Picosecond Pulses in a Dual-Wavelength Laser". Materials Science Forum 663-665 (novembre 2010): 284–87. http://dx.doi.org/10.4028/www.scientific.net/msf.663-665.284.

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Two synchronized operating modes of femtosecond and picosecond pulses, cross mode-locking and multi-pulse operating, are presented in a two-beam-pumped dual-wavelength Ti:sapphire laser. For the cross mode-locking mode, synchronized laser pulses of 37.5 fs and 0.891ps, with a timing jitter of 139 fs, are obtained in the femtosecond cavity and picosecond cavity, respectively. For the multi-pulse mode, pulses of 35 fs are obtained in the femtosecond cavity, whereas, multi-pulse mode appears in the picosecond cavity, with a pulse envelope width of 1.06 ps. The two operating modes can be switched from one to the other, dominated mainly by the mutual interaction between cross-phase modulation and self-amplitude modulation.

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Jana, Kamalesh, Amit D. Lad, Ankit Dulat, Yash M. Ved e G. Ravindra Kumar. "Ultrafast time-resolved two-dimensional velocity mapping of the hot-dense plasmas generated by intense-laser pulses". AIP Advances 12, n. 9 (1 settembre 2022): 095112. http://dx.doi.org/10.1063/5.0102048.

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Experimental measurements of spatially resolved ultrafast dynamics of the critical surface in ultra-intense laser–solid interactions are essential for a proper understanding of the physical mechanism of the interaction. Resolving ultrafast motion at both the relevant length scales (micrometers) and timescales (femtoseconds) simultaneously has been a challenging task. Here, we demonstrate a novel technique for mapping the spatiotemporal dynamics of hot and solid dense plasma created by high contrast (picosecond contrast ∼10−9) femtosecond relativistic intensity laser pulses. This pump–probe Doppler spectrometry technique offers hundreds of femtosecond temporal resolution, together with a few micrometer spatial resolution across the transverse profile of the plasma. We present the evolution of the plasma surface critical for the probe pulse at the target front as well as the rear. Early time measurements ([Formula: see text] 5 ps) using this technique provide very important information about shock wave generation and propagation and the state of the target rear.

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Spence, Stephanie, Takaaki Harada, Athanasios Margiolakis, Skylar Deckoff-Jones, Aaron N. Shugar, James F. Hamm, Keshav M. Dani e Anya R. Dani. "Applicability of Femtosecond Lasers in the Cross-section Sampling of Works of Art". MRS Advances 2, n. 33-34 (2017): 1801–4. http://dx.doi.org/10.1557/adv.2017.242.

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ABSTRACTIssues in traditional cross-section sampling of paintings and other cultural artifacts with a scalpel, such as crumbling, delamination and paint compression, can deter conservators from sampling fragile paint layers. Often, such sampling carries the risk of causing further damage from a scalpel, which outweighs the benefits of scientific investigation. Here, we show that femtosecond lasers offer a viable alternative to obtaining cross-sections with minimal damage to the surrounding artwork. A Regenerative Ti:Sapphire amplifier system with a pulse duration of 70 femtoseconds, a few milliwatts of average power and a repetition rate of 1 kHz (1000 pulses/sec) was used for the study. Tests were performed on oil paintings ranging in age from the 19th century to late 20th century. Effective settings were determined to be 2 mW of power at a speed of 10mm/sec using an 800nm laser. Preliminary results suggest femtosecond lasers could be a viable alternative for obtaining paint cross-sections when traditional sampling methods cause unnecessary damage to fragile materials.

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Neutze, Richard. "Opportunities and challenges for time-resolved studies of protein structural dynamics at X-ray free-electron lasers". Philosophical Transactions of the Royal Society B: Biological Sciences 369, n. 1647 (17 luglio 2014): 20130318. http://dx.doi.org/10.1098/rstb.2013.0318.

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X-ray free-electron lasers (XFELs) are revolutionary X-ray sources. Their time structure, providing X-ray pulses of a few tens of femtoseconds in duration; and their extreme peak brilliance, delivering approximately 10 12 X-ray photons per pulse and facilitating sub-micrometre focusing, distinguish XFEL sources from synchrotron radiation. In this opinion piece, I argue that these properties of XFEL radiation will facilitate new discoveries in life science. I reason that time-resolved serial femtosecond crystallography and time-resolved wide angle X-ray scattering are promising areas of scientific investigation that will be advanced by XFEL capabilities, allowing new scientific questions to be addressed that are not accessible using established methods at storage ring facilities. These questions include visualizing ultrafast protein structural dynamics on the femtosecond to picosecond time-scale, as well as time-resolved diffraction studies of non-cyclic reactions. I argue that these emerging opportunities will stimulate a renaissance of interest in time-resolved structural biochemistry.

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Rudenkov, A. S., V. E. Kisel, A. S. Yasukevich, K. L. Hovhannesyan, A. G. Petrosyan e N. V. Kuleshov. "Yb:CALYO-based femtosecond chirped pulse regenerative amplifier for temporally resolved pump-probe spectroscopy". Devices and Methods of Measurements 9, n. 3 (17 settembre 2018): 205–14. http://dx.doi.org/10.21122/2220-9506-2018-9-3-205-214.

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Diode-pumped femtosecond chirped pulse regenerative amplifiers based on Yb3+-materials are of practical importance for wide range of scientific, industrial and biomedical applications. The aim of this work was to study the amplification of broadband chirped femtosecond pulses in regenerative amplifier based on Yb3+:CaYAlO4crystal.Such systems use femtosecond mode-locked lasers as seed pulse sources and amplify nJ-seed pulses to sub-mJ energy range. Most chirped pulse regenerative amplifier systems described in the literature use seed lasers with typical pulse spectral width at the level of 10–15 nm full width at half maximum (FWHM) that limit the seed pulse duration of about 90 fs and amplified pulse duration at the level of 200 fs due to strong influence of gain narrowing effect on the amplified pulse parameters. Yb3+-doped crystals with wide and smooth gain bandwidth as an active medium of chirped femtosecond pulse regenerative amplification systems allow to reduce negative contribution of gain narrowing effect and lead to shortening of amplified pulses. In this research we study the chirped pulse regenerative amplification of broad-band femtosecond pulses (60 nm spectral width FWHM) in the Yb3+:CaYAlO -based chirped pulse regenerative amplifier. Substantial reduction of the amplified pulse duration down to 120 fs (19.4 nm spectral width FWHM) with average power of 3 W at 200 kHz pulse repetition frequency was demonstrated without any gain narrowing compensation technique.The results of experimental investigation of broad-band seeded Yb3+:CaYAlO -based chirped pulse regenerative amplifier are reported for the first time to our knowledge. 120 fs-pulses (19.4 nm FWHM) with average output power of 3 W were demonstrated without any gain narrowing compensation technique. Despite the significant reduction of amplified pulse duration the task of improvement group velocity dispersion balance (including high orders of group velocity dispersion) remains relevant.

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Zhu, Jianqiang, Xinglong Xie, Meizhi Sun, Qunyu Bi e Jun Kang. "A Novel Femtosecond Laser System for Attosecond Pulse Generation". Advances in Optical Technologies 2012 (15 gennaio 2012): 1–6. http://dx.doi.org/10.1155/2012/908976.

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We report a novel ultrabroadband high-energy femtosecond laser to be built in our laboratory. A 7-femtosecond pulse is firstly stretched by an eight-pass offner stretcher with a chirp rate 15 ps/nm, and then energy-amplified by a two-stage optical parametric chirped pulse amplification (OPCPA). The first stage as preamplification with three pieces of BBO crystals provides the majority of the energy gain. At the second stage, a YCOB crystal with the aperture of ~50 mm is used instead of the KDP crystal as the gain medium to ensure the shortest pulse. After the completion, the laser will deliver about 8 J with pulse duration of about 10 femtoseconds, which should be beneficial to the attosecond pulse generation and other ultrafast experiments.

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Dabu. "Femtosecond Laser Pulses Amplification in Crystals". Crystals 9, n. 7 (5 luglio 2019): 347. http://dx.doi.org/10.3390/cryst9070347.

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This paper describes techniques for high-energy laser pulse amplification in multi-PW femtosecond laser pulses. Femtosecond laser pulses can be generated and amplified in laser media with a broad emission spectral bandwidth, like Ti:sapphire crystals. By chirped pulse amplification (CPA) techniques, hundred-Joule amplified laser pulses can be obtained. Multi-PW peak-power femtosecond pulses are generated after recompression of amplified chirped laser pulses. The characteristics and problems of large bandwidth laser pulses amplification in Ti:sapphire crystals are discussed. An alternative technique, based on optical parametric chirped pulse amplification (OPCPA) in nonlinear crystals, is presented. Phase-matching conditions for broad bandwidth parametric amplification in nonlinear crystals are inferred. Ultra-broad phase matching bandwidth of more than 100 nm, able to support the amplification of sub-10 fs laser pulses, are demonstrated in nonlinear crystals, such as Beta Barium Borate (BBO), Potassium Dideuterium Phosphate (DKDP), and Lithium Triborate (LBO). The advantages and drawbacks of CPA amplification in laser crystals and OPCPA in nonlinear crystals are discussed. A hybrid amplification method, which combines low-medium energy OPCPA in nonlinear crystals with high energy CPA in large aperture laser crystals, is described. This technique is currently used for the development of 10-PW laser systems, with sub-20 fs pulse duration and more than 1012 intensity contrast of output femtosecond pulses.

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Zhu, Chang Jun, Bing Xue, Xue Jun Zhai e Jun Fang He. "Manufacture of Lasers with Multiple Operating Modes". Advanced Materials Research 482-484 (febbraio 2012): 1937–40. http://dx.doi.org/10.4028/www.scientific.net/amr.482-484.1937.

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A two-beam pumped Ti:sapphire laser with femtosecond and picosecond cavities was manufactured. Three operating modes, independent self mode-locking, cross mode-locking and multi-pulse operating, were achieved. In the independent self mode-locking mode, femtosecond and picosecond laser pulses were generated in the two cavities, respectively. In the cross mode-locking mode, synchronized femtosecond and picosecond laser pulses were obtained in the two cavities. In the multi-pulse mode, multi-pulses were produced in the picosecond cavity. The results show that, the independent self mode-locking mode is dominated mainly by group velocity dispersion and self-phase modulation, the cross mode-locking mode is governed primarily by cross-phase modulation and the multi-pulse operating is ruled largely by self-amplitude modulation.

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Golovin, Nikolai N., e Alexander K. Dmitriev. "Pulse selector for obtaining femtosecond radiation with a controlled carrier-envelope phase". Analysis and data processing systems, n. 2 (28 giugno 2022): 121–32. http://dx.doi.org/10.17212/2782-2001-2022-2-121-132.

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In non-linear optical processes, such as obtaining attosecond pulses, it is extremely important to control the carrier envelope phase. To do this, various periodic trains of identical femtosecond pulses with a controlled phase can be created. In addition, since there is no frequency comb offset in such sequences, the process of measuring optical frequencies is greatly simplified. The pulse selector has been developed to obtain a sequence of identical femtosecond pulses with a controlled carrier – envelope phase. The selector makes it possible to obtain a “pure” sequence of identical femtosecond pulses at the modulator output (when every 125th pulse is selected from the original sequence with a repetition rate of 250 MHz) in a fairly wide range of control signal phase tuning. This range is 1.3 degrees. The phase tuning of the pulse selector provides the possibility of obtaining one hundred twenty-five such sequences with a phase tuning discreteness of 2π/125. The simplest way to reduce discreteness is to increase the ratio of the pulse repetition rate of a femtosecond laser to the shift of its frequency comb. The phase characteristic of the pulse selector was obtained by registering the time dependence of the synthesized sequence with a selector phase tuning step of 0.1 degrees. We measured the spectra of the sequences at different phases of the pulse selector, as well as the emission spectrum of the master laser at the minimum transmission of the modulator in the absence of modulation. The spectrum with the maximum amplitude corresponded to the case when identical pulses with the highest amplitude were selected from the original sequence. The difference between these spectra made it possible to isolate the spectrum of a pure sequence of identical femtosecond pulses without taking into account the "background" that occurs due to the modulator has a finite attenuation of –20 dB.

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Wang, Huai Sheng. "The Temporal Diffraction Characteristic of a Femtosecond Laser Pulse by a Serrated Aperture". Applied Mechanics and Materials 268-270 (dicembre 2012): 1353–56. http://dx.doi.org/10.4028/www.scientific.net/amm.268-270.1353.

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Based on Fresnel diffraction theory we give out the light field distribution for the definite frequency component of a femtosecond laser pulse when the laser pulse passes through a serrated aperture. Through an inverse Fourier transformation, we get the temporal diffraction field function of the femtosecond laser pulse at any distance. The temporal diffraction field function is related to the width of the laser pulse, the structure of the serrated aperture, the Fresnel number at central frequency and time. Number calculation shows when the width of the laser pulse is within a few tens of femtoseconds and Fresnel number at central frequency is much, the temporal diffraction intensity is not a Gaussian distribution. Nevertheless when Fresnel number at central frequency is less than ten, the temporal diffraction intensity can be approximately regarded as a Gaussian distribution and has a time delay effect.

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Obata, Kotaro, Francesc Caballero-Lucas, Shota Kawabata, Godai Miyaji e Koji Sugioka. "GHz bursts in MHz burst (BiBurst) enabling high-speed femtosecond laser ablation of silicon due to prevention of air ionization". International Journal of Extreme Manufacturing 5, n. 2 (11 aprile 2023): 025002. http://dx.doi.org/10.1088/2631-7990/acc0e5.

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Abstract For the practical use of femtosecond laser ablation, inputs of higher laser intensity are preferred to attain high-throughput material removal. However, the use of higher laser intensities for increasing ablation rates can have detrimental effects on ablation quality due to excess heat generation and air ionization. This paper employs ablation using BiBurst femtosecond laser pulses, which consist of multiple bursts (2 and 5 bursts) at a repetition rate of 64 MHz, each containing multiple intra-pulses (2–20 pulses) at an ultrafast repetition rate of 4.88 GHz, to overcome these conflicting conditions. Ablation of silicon substrates using the BiBurst mode with 5 burst pulses and 20 intra-pulses successfully prevents air breakdown at packet energies higher than the pulse energy inducing the air ionization by the conventional femtosecond laser pulse irradiation (single-pulse mode). As a result, ablation speed can be enhanced by a factor of 23 without deteriorating the ablation quality compared to that by the single-pulse mode ablation under the conditions where the air ionization is avoided.

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Lu, Qi, Xiang Zhang, Arnaud Couairon e Yi Liu. "Revealing Local Temporal Profile of Laser Pulses of Intensity above 1014 W/cm2". Sensors 23, n. 6 (14 marzo 2023): 3101. http://dx.doi.org/10.3390/s23063101.

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We demonstrated a method for in situ temporal characterization of an intense femtosecond laser pulse around its focus where the laser intensity exceeds 1014 W/cm2. Our method is based on the second harmonic generation (SHG) by a relatively weak femtosecond probe pulse and the intense femtosecond pulses under analysis in the gas plasma. With the increase in the gas pressure, it was found that the incident pulse evolves from a Gaussian profile to a more complicated structure featured by multiple peaks in the temporal domain. Numerical simulations of filamentation propagation support the experimental observations of temporal evolution. This simple method can be applied to many situations involving femtosecond laser–gas interaction, when the temporal profile of the femtosecond pump laser pulse with an intensity above 1014 W/cm2 cannot be measured in traditional ways.

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Chen, Gao. "Isolated attosecond pulse generation from helium atom irradiated by a three-color laser pulse". Acta Physica Sinica 71, n. 5 (2022): 054204. http://dx.doi.org/10.7498/aps.71.20211502.

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Isolated attosecond pulses enables the studying and controlling of ultrafast electron processes in atoms and molecules. High-order harmonic generation (HHG) is the most promising way to generate such pulses, benefiting from the broad plateau structure of the typical HHG spectrum. We theoretically investigate high-order harmonic and attosecond pulse generation from helium atom in a three-color laser field, which is synthesized by 16 fs/1600 nm, 15 fs/1100 nm and 5 fs/800 nm pulse laser. Compared with harmonic spectrum generated by a two-color laser field synthesized by 16 fs/1600 nm and 15 fs/1100 nm, the harmonic spectrum generated from the synthesized three-color field exhibits high conversion efficiency and broadband supercontinuum characteristics. The continuous spectrum range covers from 230th to 690th harmonics, and the generation of 128 attosecond isolated short pulses with higher intensity is realized after Fourier transform. This result is attributable to the fact that the synthesized three-color electric field exhibits high-intensity and few-cycle mid-infrared femtosecond pulse laser characteristics, which can effectively control atomic ionization and recombination occurring within an effective optical period of the mid-infrared femtosecond pulse. This scheme solves the problems faced by the current femtosecond pulse laser technology, i.e. the few-cycle mid-infrared femtosecond pulse laser cannot have both carrier envelope phase stability and high power output.

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Jiang, Lan, e Hai-Lung Tsai. "Energy Transport and Nanostructuring of Dielectrics by Femtosecond Laser Pulse Trains". Journal of Heat Transfer 128, n. 9 (2 maggio 2006): 926–33. http://dx.doi.org/10.1115/1.2241979.

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This study analyzes single burst ablation of dielectrics by a femtosecond pulse train that consists of one or multiple pulses. It is found that (1) there exist constant-ablation-depth zones with respect to fluence for one or multiple pulses per train and (2) for the same total fluence per train, although the ablation depth decreases in multiple pulses as compared to that of a single pulse, the depth of the constant-ablation-depth zone decreases. In other words, repeatable structures at the desired smaller nanoscales can be achieved in dielectrics by using the femtosecond pulse train technology, even when the laser fluence is subject to fluctuations. The predicted trends are in agreement with published experimental data.

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SCHMIDT, M., P. D'OLIVEIRA, P. MEYNADIER, D. NORMAND e C. CORNAGGIA. "STRONG LASER FIELD INTERACTION WITH DIATOMIC MOLECULES: FROM THE ULTRA-SHORT TO LONG-PULSE REGIME". Journal of Nonlinear Optical Physics & Materials 04, n. 04 (ottobre 1995): 817–29. http://dx.doi.org/10.1142/s0218863595000367.

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In the present paper, we compare novel MEDI results on iodine obtained with 30 ps laser pulses to those obtained in the femtosecond regime. The results indicate laser-induced trapping of the molecules not only in the ultra-short pulse regime, but also for the long pulses, since the fragment kinetic energy releases are essentially the same, although the pulse duration is varied over more than two orders of magnitude. Most interestingly, with 30 ps pulses significant post-dissociation ionization of the In+-fragments observed for the first time, proving that near-Coulomb energies and post-dissociation ionization can be observed simultaneously. A femtosecond double-pulse experiment confirms our recent hypothesis of molecular stabilization governing the MEDI interaction.

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Aquila, A., M. Drescher, T. Laarmann, M. Barthelmeß, H. N. Chapman e S. Bajt. "Moving the Frontier of Quantum Control into the Soft X-Ray Spectrum". International Journal of Optics 2011 (2011): 1–4. http://dx.doi.org/10.1155/2011/417075.

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The femtosecond nature of X-ray free electron laser (FEL) pulses opens up exciting research possibilities in time-resolved studies including femtosecond photoemission and diffraction. The recent developments of seeding X-ray FELs extend their capabilities by creating stable, temporally coherent, and repeatable pulses. This in turn opens the possibility of spectral engineering soft X-ray pulses to use as a probe for the control of quantum dynamics. We propose a method for extending coherent control pulse-shaping techniques to the soft X-ray spectral range by using a reflective geometry 4f pulse shaper. This method is based on recent developments in asymmetrically cut multilayer optic technology and piezoelectric substrates.

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Sano, Tomokazu, Kengo Takahashi, Akio Hirose e Kojiro F. Kobayashi. "Femtosecond Laser Ablation of Zr₅₅Al₁₀Ni₅Cu₃₀ Bulk Metallic Glass". Materials Science Forum 539-543 (marzo 2007): 1951–54. http://dx.doi.org/10.4028/www.scientific.net/msf.539-543.1951.

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Dependence of the femtosecond laser ablation depth on the laser pulse energy was investigated for Zr55Al10Ni5Cu30 bulk metallic glass. Investigation of the femtosecond laser ablation of bulk metallic glasses has not been reported. Femtosecond laser pulses (wavelength of 800 nm, pulse width of 100 fs, pulse energies of 2 – 900 μJ) were focused and irradiated on the polished surface of metals in air. The ablation depth of the metallic glass is deeper than that of its crystallized metal at a pulse energy in the strong ablation region. We suggest that the energy loss at grain boundaries of hot electrons which is accelerated by the laser electric field influence the ablation depth in the strong ablation region.

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Alshehria, A. M., El Sayed Yousefa, A. A. Alshahrania, Akram Ibrahima, Nafis Ahmada e V. R. Bhardwajb. "Differential Nonlinear Absorption of an Elliptically Polarized Femtosecond Vortex Beam in Tellurite Glass-=SUP=-*-=/SUP=-". Журнал технической физики 128, n. 8 (2020): 1178. http://dx.doi.org/10.21883/os.2020.08.49718.293-19.

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We present differential nonlinear absorption of an elliptically polarized femtosecond laser vortex beam carrying an angular momentum of l = -1 in tellurite glass. Transmission measurements were utilized to measure the nonlinear absorption of the glass on a shot-by-shot basis, and to investigate the modification threshold for the beam. Additionally, the effect of pulse energy on the polarization ellipse was investigated. The results revealed a reduction in the ellipticity as the incident pulse energy was increased. Non-rotation of the ellipsoid indicated that there is no change in the third order nonlinear susceptibility (chi(3)) of the telluride glass upon irradiation by the femtosecond beam. The transmission of multiple pulses through the same spot revealed that although an effect was evident for the first ten pulses, the subsequent pulses had no effect. The transmission of a complete cycle of increasing and decreasing pulse energies revealed no hysteresis of the femtosecond laser vortex beam in tellurite glass in contrast to that reported for Gaussian beams in silica glass. Keywords: vortex beam, tellurite glass, nonlinear absorption.

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Mir, Hanan, Fabian Meyer, Andreas A. Brand, Katrin Erath-Dulitz e Jan Frederik Nekarda. "Study of GHz-Burst Femtosecond Laser Micro-Punching of 4H-SiC Wafers". Solid State Phenomena 344 (6 giugno 2023): 29–33. http://dx.doi.org/10.4028/p-q6725d.

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The micromaching of silicon carbide using femtosecond laser pulses is becoming an important field of research. High-repetition-rate sub-pulse trains, so-called pulse bursts, are a particularly promising route towards completely new process regimes. We report on the results of micro-punching n-type 4H-silicon carbide wafers using GHz pulse burst in order to systematically investigate the influence of the temporal energy distribution on laser processing. Pulse-burst experiments are performed at a laser wavelength of λ= 1030 nm using a single GHz burst containing a varying number of pulses and then compared with standard single femtosecond pulse exposures. The pulse energy is swept across the ablation threshold. For each set of parameters, the micromachining efficiency is evaluated in terms of ablation efficiency and burr characteristics. Scanning electron micrographs provide qualitative information about the machining quality. The characteristics of the laser modification are discussed in relation to an increase in the number of pulses in a burst envelope and to an increase in pulse energy. We observe that, compared to a single pulse, a GHz burst comprised of 10 lower-energy pulses leads to an increase in the ablation rate by a factor of ≤ 10.

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GUO, ZHONGYI, WEIQIANG DING, SHILIANG QU, JINGMIN DAI e SHUTIAN LIU. "SELF-ASSEMBLED VOLUME GRATING IN SILICA GLASS INDUCED BY TIGHTLY FOCUSED FEMTOSECOND LASER PULSE". Journal of Nonlinear Optical Physics & Materials 18, n. 04 (dicembre 2009): 625–32. http://dx.doi.org/10.1142/s0218863509004841.

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We report on self-assembled volume grating in silica glass induced by a tightly focused femtosecond laser pulse. The formation of volume grating is attributed to the multiple microexplosion in the transparent materials induced by the femtosecond pulses. The first order diffractive efficiency is greatly dependent on the energy of the pulses and the scanning velocity of the laser, and the highest reaches to nearly 30%.

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Bibicheva S. A., Rupasov A. E., Danilov P. A., Ionin N. A., Smirnov N. A, Kudryashov S. N., Shelygina R. A. e Zakoldaev R. A. "Self-organizing half-wave gratings on the surface of silica glass". Optics and Spectroscopy 130, n. 4 (2022): 437. http://dx.doi.org/10.21883/eos.2022.04.53732.58-21.

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The interaction of femtosecond laser pulses with the surface of silica glass has been studied. As a result of interference between the incident radiation and surface plasmon polaritons, the formation of self-organizing subwavelength periodic structures with a period of 250 nm was observed. The minimum pulse energy at which recording occurs without surface ablation has been revealed. Keywords: direct laser recording, femtosecond laser pulses, silica, nanogratings.

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26

Arkhipov M. V., Arkhipov R. M. e Rosanov N. N. "Generation of unipolar pulses of terahertz radiation with a large electric area". Optics and Spectroscopy 130, n. 8 (2022): 980. http://dx.doi.org/10.21883/eos.2022.08.54771.3703-22.

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Abstract (sommario):

A physical situation is proposed and theoretically analyzed, in which, in our opinion, it is possible to generate unipolar terahertz pulses with a large electric area. In this case, the gas in the tube is excited by a femtosecond IR laser pulse. In this case, the tube with gas is placed in a constant external electric field. The generation of a unipolar pulse is based on "three-step scheme" --- ionization of gas atoms by a femtosecond pulse, subsequent acceleration of a free electron in a dc external field and subsequent annihilation of an electron upon collision with a tube wall or another atom (ion). Keywords: unipolar pulses, ultrafast optics, electric pulse area, terahertz radiation, three-step model.

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27

Ghaforyan, H., R. Sadighi-Bonabi e E. Irani. "The Effect of Chirped Intense Femtosecond Laser Pulses on the Argon Cluster". Advances in High Energy Physics 2016 (2016): 1–9. http://dx.doi.org/10.1155/2016/2609160.

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Abstract (sommario):

The interaction of intense femtosecond laser pulses with atomic Argon clusters has been investigated by using nanoplasma model. Based on the dynamic simulations, ionization process, heating, and expansion of a cluster after irradiation by femtosecond laser pulses at intensities up to 2×1017 Wcm−2are studied. The analytical calculation provides ionization rate for different mechanisms and time evolution of the density of electrons for different pulse shapes. In this approach, the strong dependence of laser intensity, pulse duration, and laser shape on the electron energy, the electron density, and the cluster size is presented using the intense chirped laser pulses. Based on the presented theoretical modifications, the effect of chirped laser pulse on the complex dynamical process of the interaction is studied. It is found that the energy of electrons and the radius of cluster for the negatively chirped pulses are improved up to 20% in comparison to the unchirped and positively chirped pulses.

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28

Kuzmin E. V. e Klekovkin A.V. "Features of structuring and ablation of thin titanium films by femtosecond laser pulses". Optics and Spectroscopy 130, n. 4 (2022): 412. http://dx.doi.org/10.21883/eos.2022.04.53727.66-21.

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The processes of structuring and ablation of a titanium film by femtosecond laser pulses at wavelengths of 515 nm and 1030 nm have been studied in both single-pulse and multi-pulse modes. The optimal energy regimes for the selective removal of film material without damaging the substrate, as well as the regimes for the generation of the periodic structures on the surface, are determined. The evolution of periodic structures with an increase in the number of laser pulses is shown. The precision removal of titanium film is associated with thermomechanical explosive boiling and the corresponding energy contribution, which ensures the cascade appearance of ablation craters.. Keywords: thin films, femtosecond laser pulses, surface treatment

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29

Shi, Wei, Lei Yang, Lei Hou, Zenan Liu, Nuo Xu e Zhiyang Xing. "Positive and Negative Symmetric Pulses with Fast Rising Edge Generated from a GaAs Photoconductive Semiconductor Switch". Applied Sciences 9, n. 2 (21 gennaio 2019): 358. http://dx.doi.org/10.3390/app9020358.

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In this paper, the positive and negative symmetric pulses with a fast rising edge were generated by a GaAs photoconductive semiconductor switch (PCSS). When the GaAs PCSS was biased at 2.0 kV and triggered by a femtosecond laser pulse with a pulse energy of 97.5 J, the peak voltages of the positive and negative pulses were 1.313 kV and 1.329 kV, respectively, and the rise times were 174 ps and 164 ps, respectively. Moreover, the GaAs PCSS presents good stability. The experimental results show that GaAs PCSSs can meet the requirement of a femtosecond streak camera.

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30

Hassan, Mohammed T., Haihua Liu, John Spencer Baskin e Ahmed H. Zewail. "Photon gating in four-dimensional ultrafast electron microscopy". Proceedings of the National Academy of Sciences 112, n. 42 (5 ottobre 2015): 12944–49. http://dx.doi.org/10.1073/pnas.1517942112.

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Ultrafast electron microscopy (UEM) is a pivotal tool for imaging of nanoscale structural dynamics with subparticle resolution on the time scale of atomic motion. Photon-induced near-field electron microscopy (PINEM), a key UEM technique, involves the detection of electrons that have gained energy from a femtosecond optical pulse via photon–electron coupling on nanostructures. PINEM has been applied in various fields of study, from materials science to biological imaging, exploiting the unique spatial, energy, and temporal characteristics of the PINEM electrons gained by interaction with a “single” light pulse. The further potential of photon-gated PINEM electrons in probing ultrafast dynamics of matter and the optical gating of electrons by invoking a “second” optical pulse has previously been proposed and examined theoretically in our group. Here, we experimentally demonstrate this photon-gating technique, and, through diffraction, visualize the phase transition dynamics in vanadium dioxide nanoparticles. With optical gating of PINEM electrons, imaging temporal resolution was improved by a factor of 3 or better, being limited only by the optical pulse widths. This work enables the combination of the high spatial resolution of electron microscopy and the ultrafast temporal response of the optical pulses, which provides a promising approach to attain the resolution of few femtoseconds and attoseconds in UEM.

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31

Tollerud, Jonathan Owen, Giorgia Sparapassi, Angela Montanaro, Shahaf Asban, Filippo Glerean, Francesca Giusti, Alexandre Marciniak et al. "Femtosecond covariance spectroscopy". Proceedings of the National Academy of Sciences 116, n. 12 (28 febbraio 2019): 5383–86. http://dx.doi.org/10.1073/pnas.1821048116.

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Abstract (sommario):

The success of nonlinear optics relies largely on pulse-to-pulse consistency. In contrast, covariance-based techniques used in photoionization electron spectroscopy and mass spectrometry have shown that a wealth of information can be extracted from noise that is lost when averaging multiple measurements. Here, we apply covariance-based detection to nonlinear optical spectroscopy, and show that noise in a femtosecond laser is not necessarily a liability to be mitigated, but can act as a unique and powerful asset. As a proof of principle we apply this approach to the process of stimulated Raman scattering in α-quartz. Our results demonstrate how nonlinear processes in the sample can encode correlations between the spectral components of ultrashort pulses with uncorrelated stochastic fluctuations. This in turn provides richer information compared with the standard nonlinear optics techniques that are based on averages over many repetitions with well-behaved laser pulses. These proof-of-principle results suggest that covariance-based nonlinear spectroscopy will improve the applicability of fs nonlinear spectroscopy in wavelength ranges where stable, transform-limited pulses are not available, such as X-ray free-electron lasers which naturally have spectrally noisy pulses ideally suited for this approach.

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32

Qi, Li Tao, e Jin Ping Hu. "Experimental Investigation on Femtosecond Laser Ablation of Polycarbonate". Advanced Materials Research 652-654 (gennaio 2013): 2359–62. http://dx.doi.org/10.4028/www.scientific.net/amr.652-654.2359.

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Abstract (sommario):

In this paper, experimental investigations on femtosecond laser (pulse duration:164 fs, wavelength:780 nm) micromachining of polycarbonate have been carried out in air. The lateral and vertical machining precision was evaluated by scanning electron microscopy and profilometer. The morphological changes were observed by scanning electron microscopy. The ablation mechanism varied with the laser pulse energy was discussed. The diameter and depth of the ablated crated are influenced by the laser pulse energy and the number of laser pulses. The relation between the diameter and ablation depth of the crater and the key parameters of femtosecond laser is obtained. Femtosecond laser micromachining of polycarbonate have a potential application of the fabrication of polycarbonate-based devices.

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33

Tikhomirov, S. A. "Femtosecond System with Pulse Pumping of Seed Laser and Amplifier by Using a Single Power Unit". Devices and Methods of Measurements 12, n. 1 (19 marzo 2021): 23–29. http://dx.doi.org/10.21122/2220-9506-2021-12-1-23-29.

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For several decades development of methods for generating ultrashort pulses has been an independent urgent scientific and technical problem. There is a constant improvement both in the methods of such pulses receiving and in methods of their use. The aim of this work was to investigate the possibility of realizing the coordinated operation of two fundamentally different types of pump lasers for the femtosecond oscillator and amplifier based on one single-lamp laser head and to create on this basis a compact high-power femtosecond system with pulsed pumping and one power unit.The practical implementation of two types of pulsed lasers (nano- and picosecond ones operating, respectively, in Q-switch and modelock regime) on a single laser head with two active elements and one pump lamp is carried out. The required synchronization in time the pump pulse femtosecond amplifier formation and quasi-stationary region of generated pulses in the output radiation of a femtosecond Ti:sapphire is obtained.On this basis a compact, pulse pumped monoblock laser system has been developed that can generate femtosecond pulses with a duration of 50–150 fs with an energy up to 1 mJ and a high enough pulse repetition rate (up to 1 kHz which is determined by the type of laser head and pump unit used). In the developed laser system a compact scheme of a stretcher-compressor with a single common diffraction grating is used.Laser systems of this type characterized by a relatively low cost due to the use of a single power supply unit for simultaneous pumping of the amplifier and oscillator, as well as lower requirements for the quality of optical elements and usage conditions due to the pulse mode of operation, are quite practical and can be used both in scientific research in the field of ultra-high-speed kinetic spectroscopy and nonlinear optics, as well as in numerous technical applications, particular in the precision processing of materials, as optical simulators of the action of heavy charged particles in testing the radiation resistance of integrated circuits and electronic modules.

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34

Balachninaitė, O., J. Skruibis, A. Matijošius e V. Vaičaitis. "Temporal and spatial properties of plasma induced by infrared femtosecond laser pulses in air". Plasma Sources Science and Technology 31, n. 4 (1 aprile 2022): 045001. http://dx.doi.org/10.1088/1361-6595/ac5c62.

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Abstract Space and time-resolved electron density and temperature of the plasma, created in air by focused femtosecond laser pulses have been investigated as a function of the pump pulse energy and duration. For the air ionization the infrared (1030 nm) femtosecond (190–500 fs) Yb:KGW laser pulses of up to 1 mJ energy were used. Based on the Stark broadening of the oxygen-I 777.19 nm line we have found that after establishing a local equilibrium the density of laser-created plasma could exceed 1017 cm−3 with the electron temperature of over 5000 °C. Obtained results agree well with the results of previously reported measurements of the plasma density created by the femtosecond near-infrared Ti:sapphire laser pulses.

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35

Qi, Li Tao, e Jin Ping Hu. "Femtosecond Laser Micromachining of High Quality Groove on Sapphire Surface". Applied Mechanics and Materials 217-219 (novembre 2012): 2213–16. http://dx.doi.org/10.4028/www.scientific.net/amm.217-219.2213.

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Abstract (sommario):

In this paper, high quality grooves were fabricated by femtosecond laser pulse on sapphire surface. Grooves were fabricated under different experimental conditions. The lateral and vertical machining precision was evaluated by scanning electron microscopy and profilometer. High quality grooves could be obtained at the condition of low pulse energy, high scanning-speed and increasing the number of laser scans. The relationship between the width and depth of the groove and the key parameters of femtosecond laser micromachining system was studied. Several samples of the high quality grooves were obtained by femtosecond laser pulses. High quality grooves have a potential application of the fabrication of sapphire-based devices.

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36

Yang, Jinfeng, Kazuki Gen, Nobuyasu Naruse, Shouichi Sakakihara e Yoichi Yoshida. "A Compact Ultrafast Electron Diffractometer with Relativistic Femtosecond Electron Pulses". Quantum Beam Science 4, n. 1 (20 gennaio 2020): 4. http://dx.doi.org/10.3390/qubs4010004.

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We have developed a compact relativistic femtosecond electron diffractometer with a radio-frequency photocathode electron gun and an electron lens system. The electron gun generated 2.5-MeV-energy electron pulses with a duration of 55 ± 5 fs containing 6.3 × 104 electrons per pulse. Using these pulses, we successfully detected high-contrast electron diffraction images of single crystalline, polycrystalline, and amorphous materials. An excellent spatial resolution of diffraction images was obtained as 0.027 ± 0.001 Å−1. In the time-resolved electron diffraction measurement, a laser-excited ultrafast electronically driven phase transition in single-crystalline silicon was observed with a temporal resolution of 100 fs. The results demonstrate the advantages of the compact relativistic femtosecond electron diffractometer, including access to high-order Bragg reflections, single shot imaging with the relativistic femtosecond electron pulse, and the feasibility of time-resolved electron diffraction to study ultrafast structural dynamics.

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37

Nan, Junyi, Min Li, Ling Zhang, Shuai Yuan, Boqu He e Heping Zeng. "Terahertz and Photoelectron Emission from Nanoporous Gold Films on Semiconductors". Nanomaterials 9, n. 3 (12 marzo 2019): 419. http://dx.doi.org/10.3390/nano9030419.

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Efficient terahertz and photoelectron emission were observed from nano-porous gold (NPG) films deposited on an intrinsic gallium arsenide (GaAs) semiconductor substrate stimulated by femtosecond laser with pulse width of 60 fs. Time-domain THz emission and reflection spectroscopy confirmed that the free charges accelerated by irradiated femtosecond laser pulses transferred from the NPG films into the GaAs substrates. Accordingly, charges accumulation was reduced in the NPG films, resulting in a stronger emission of THz pulse than that from NPG films deposited on SiO2 substrate. Charges injected into the GaAs substrate enforced an observable decrease of the THz refractive index proportional to the intensity of incident light. In comparison, for NPG deposited on glass substrates, laser induced free charges were accumulated in the NPG films, and femtosecond laser pulses irradiating on the NPG films made no changes of the THz refractive index of the glass substrates.

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38

Liu, Yongshan, Houyi Cheng, Pierre Vallobra, Huiwen Wang, Sylvain Eimer, Xiaoqiang Zhang, Gregory Malinowski et al. "Ultrafast single-pulse switching of Tb-dominant CoTb alloy". Applied Physics Letters 122, n. 2 (9 gennaio 2023): 022401. http://dx.doi.org/10.1063/5.0131716.

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Abstract (sommario):

Single-pulse magnetization switching by femtosecond laser pulses is the fastest way to manipulate magnetization. To date, among rare-earth transition metal alloys, single-pulse switching is limited to Gd-based structures. Here, we demonstrate ultrafast single-pulse switching of Tb-dominant CoTb alloys within several tens of picoseconds. Our further analysis shows that the ultrafast magnetization reversal is linked to ultrafast heating of laser pulses and an external field.

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39

JIANG, YUQIANG, CUNGEN MA, ISAMU OH, YOICHIROH HOSOKAWA e HIROSHI MASUHARA. "SECONDARY CONVERGENCE IN FEMTOSECOND LASER TRAPPING". Modern Physics Letters B 24, n. 16 (30 giugno 2010): 1739–46. http://dx.doi.org/10.1142/s0217984910024110.

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Abstract (sommario):

When femtosecond laser pulses pass through a trapped polystyrene bead, water breakdown is induced even though the energy of laser pulse is much lower compared to the threshold value of breakdown when the femtosecond laser directly irradiates in water. This mechanism is assigned to the secondary convergence of the laser by the trapped bead.

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40

Peiyu, Xia, Lu Faming, Ishii Nobuhisa, Kanai Teruto e Itatani Jiro. "Generation of sub-two-cycle CEP-stable optical pulses at 3.5 μm by multiple-plate pulse compression for high-harmonic generation in crystals". EPJ Web of Conferences 205 (2019): 01006. http://dx.doi.org/10.1051/epjconf/201920501006.

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Abstract (sommario):

Multiple-plate pulse compression of femtosecond mid-infrared pulses is demonstrated using YAG and Si windows. With this robust compression scheme, we produce sub-two-cycle, CEP-stable optical pulses and observe CEP-dependent high harmonic generation in crystals.

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41

Shaheen, Mohamed E., e Brian J. Fryer. "Femtosecond laser ablation of brass: A study of surface morphology and ablation rate". Laser and Particle Beams 30, n. 3 (10 luglio 2012): 473–79. http://dx.doi.org/10.1017/s0263034612000407.

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AbstractThe interaction of near infrared femtosecond laser pulses with a Cu based alloy (brass) in ambient air at atmospheric pressure and under different laser conditions was investigated. The effects of laser fluence and number of pulses on surface morphology and ablation rate were studied using scanning electron microscopy (SEM) and optical microscopy. Ablation rates were found to rapidly increase from 83 to 604 nm/pulse in the fluence range 1.14–12.21 J/cm2. At fluence >12.21 J/cm2, ablation rates increased slowly to a maximum (607 nm/pulse at 19.14 J/cm2), and then decreased at fluence higher than 20.47 J/cm2 to 564 nm/pulse at 24.89 J/cm2. Large amounts of ablated material in a form of agglomerated fine particles were observed around the ablation craters as the number of laser pulses and fluence increased. The study of surface morphology shows reduced thermal effects with femtosecond laser ablation in comparison to nanosecond laser ablation at low fluence.

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42

Milchberg, H. M., K. Y. Kim, V. Kumarappan, B. D. Layer e H. Sheng. "Clustered gases as a medium for efficient plasma waveguide generation". Philosophical Transactions of the Royal Society A: Mathematical, Physical and Engineering Sciences 364, n. 1840 (24 gennaio 2006): 647–61. http://dx.doi.org/10.1098/rsta.2005.1729.

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Clustered gas jets are shown to be an efficient means for plasma waveguide generation, for both femtosecond and picosecond generation pulses. These waveguides enable significantly lower on-axis plasma density (less than 10 18 cm −3 ) than in conventional hydrodynamic plasma waveguides generated in unclustered gases. Using femtosecond pump pulses, self-guided propagation and strong absorption (more than 70%) are used to produce long centimetre scale channels in an argon cluster jet, and a subsequent intense pulse is coupled into the guide with 50% efficiency and guided at above 10 17 W cm −2 intensity over 40 Rayleigh lengths. We also demonstrate efficient generation of waveguides using 100 ps axicon-generated Bessel-beam pump pulses. Despite the expected sub-picosecond cluster disassembly time, we observe long pulse absorption efficiencies up to a maximum of 35%. Simulations show that in the far leading edge of the long laser pulse, the volume of heated clusters evolves to a locally uniform and cool plasma already near ionization saturation, which is then efficiently heated by the remainder of the pulse.

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43

Sitnikov, Dmitry S., Maxim A. Filatov e Inna V. Ilina. "Optimal Exposure Parameters for Microsurgery of Embryo Zona Pellucida Using Femtosecond Laser Pulses". Applied Sciences 13, n. 20 (12 ottobre 2023): 11204. http://dx.doi.org/10.3390/app132011204.

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We applied femtosecond laser pulses for microsurgery of the zona pellucida (ZP) of mouse embryos in terms of assisted reproductive technologies. The embryos were subjected to a series of laser pulses (wavelength of 514 nm, pulse duration of 280 fs, repetition rate of 2.5 kHz). Optical microscopy was used to study the dependence of the ZP cut width on the pulse energy E and velocity v of the laser beam. It is shown that the same value of the cut width can be obtained for different combinations of these parameters. The boundaries of admissible values were found to be E = (19–52) nJ, v = (0.001–0.03) mm/s; recommendations on their proper choice are given. An analytical expression of the cut width of the ZP for a given combination of laser-pulse energy, beam velocity, and pulse repetition rate is proposed. This simple and easy-to-use equation allows for quick prediction of ZP cut width in embryo microsurgery procedures of laser-assisted hatching and embryo laser tagging using femtosecond laser pulses.

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44

Zhang, Lei, Xiao Wen Cao, Shun Guang Li, Ru Yi Xiang e Hui Chao Sun. "Investigation of Femtosecond Laser Ablation Threshold for Nickel Template". Applied Mechanics and Materials 633-634 (settembre 2014): 665–70. http://dx.doi.org/10.4028/www.scientific.net/amm.633-634.665.

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This paper presents a theoretical and experimental investigation into the ablation threshold of nickel template by femtosecond laser in air at atmospheric pressure. The laser pulses used for the study are 800 nm in wavelength, 100fs in pulse duration, and 1KHz in repetition rate. The two-temperature model is used to predict the single-pulse ablation threshold for nickel theoretically. Micro-hole ablation experiments are carried out in air by focusing the femtosecond laser beam on the nickel target surface at normal incidence with the long-focus objective lens of enlargement factor 50 and NA=0.7 to determine the single-pulse and multi-pulse ablation thresholds for nickel by setting up the relationship between the measured hole diameters and the pulse energies. The single pulse ablation threshold of 4132.98 Jm-2obtained experimentally is very close to that of 3907.99 Jm-2predicted by two-temperature model. The incubation factorξ, which describes the changes of the multi-pulse ablation thresholds with the number of pulses, is determined to be 0.812 for nickel.

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Nedyalkov, N., A. Dikovska, T. Dilova e G. Atanasova. "Influence of the pulse duration at the laser processing of nitride ceramics". Journal of Physics: Conference Series 2710, n. 1 (1 febbraio 2024): 012014. http://dx.doi.org/10.1088/1742-6596/2710/1/012014.

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Abstract This paper presents results on laser ablation of AlN and Si3N4 ceramics by laser pulses with different duration. Three types of laser systems, a Nd:YAG one, operated at wavelength of 1064 nm and pulse duration of 15 ns, a Nd:YAG, operated at wavelength of 1064 nm and pulse duration of 10 ps, and a femtosecond laser system, operated at 800 nm, with a pulse duration of 75 fs, are used for experiments. Details on the ablation efficiency, surface morphology, and the chemical composition of the irradiated zones as a function of the pulse duration are given and discussed. It is demonstrated that the ablation rate (ablation depth per pulse) is highest for processing with nanosecond pulses and it is lowest for the femtosecond regime. The laser ablation results in significant change of the surface morphology, as its characteristics are influenced by the pulse duration. For all pulse durations conditions for formation of ripples structures are found. The ablation process is realized by decomposition of the ceramics and the composition of the remaining surface layer is governed by oxidation and carbonization.

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46

Брехов, К. А., К. А. Гришунин, Д. В. Афанасьев, С. В. Семин, Н. Э. Шерстюк, Е. Д. Мишина e А. В. Кимель. "Генерация второй оптической гармоники и ее фотоиндуцированная динамика в сегнетоэлектрике-полупроводнике Sn-=SUB=-2-=/SUB=-P-=SUB=-2-=/SUB=-S-=SUB=-6-=/SUB=-". Физика твердого тела 60, n. 1 (2018): 33. http://dx.doi.org/10.21883/ftt.2018.01.45285.179.

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AbstractBy means of optical pump–probe technique, the ultrafast dynamics of nonlinear optical response of the ferroelectric semiconductor Sn_2P_2S_6 crystal excited with a femtosecond laser pulse has been investigated. It has been shown that, under the action of femtosecond pulses, change in optical second harmonic generation occurs in the sample, which can be due to screening of existing electric polarization.

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47

Pajic, Bojan, Brigitte Pajic-Eggspuehler, Christian Rathjen, Mirko Resan e Zeljka Cvejic. "Why Use Ultrashort Pulses in Ophthalmology and Which Factors Affect Cut Quality". Medicina 57, n. 7 (8 luglio 2021): 700. http://dx.doi.org/10.3390/medicina57070700.

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The power density of femtosecond lasers and exposure time to the tissue are crucial for a successful procedure in terms of safety and precision. The reduction of the pulse duration allows reducing the quantity of the energy to be delivered to the tissue for disruption with strongly diminished mechanical and thermal collateral damage. The cutting effect of ultra-short pulses is very precise, minimally traumatic, safe, and predictable. Future developments will lead to further energy reductions to achieve optical breakdowns. However, the pulse length cannot be shortened arbitrarily because below 100 fs nonlinear effects can change the process in an unfavorable way. Compared to manual-conventional cataract surgery, femtosecond laser-assisted cataract surgery (FLACS) shows many advantages in clinical application, especially with regard to precision and tissue protection. The femtosecond laser has become particularly important and has made the overall procedure safer when we deal with complex cataract cases such as subluxated lenses. We provide an overview of the evolution of femtosecond laser technology for use in refractive and cataract surgeries. This article describes the advantages of available laser platforms with ultrashort pulses and mainly focuses on the technical and physical backgrounds of ophthalmic surgery technologies.

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48

Manzoni, Cristian, e Giulio Cerullo. "Parametric nonlinear optics". Photoniques, n. 122 (2023): 46–51. http://dx.doi.org/10.1051/photon/202312246.

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Abstract (sommario):

Many scientific and technological applications require the generation of broadly tunable femtosecond light pulses. Optical parametric amplifiers (OPAs) exploit second-order nonlinear interactions to convert a high-power fixed wavelength pulse (the pump) into a tunable pulse (the signal). This paper reviews the principles of OPAs and highlights their capability to generate few-optical-cycle pulses with high energy and carrier-envelope-phase stability.

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49

Blonskyi, I. V., V. M. Kadan, S. V. Pavlova, I. A. Pavlov, O. I. Shpotyuk e O. K. Khasanov. "Ultrashort Light Pulses in Transparent Solids: Propagation Peculiarities and Practical Applications". Ukrainian Journal of Physics 64, n. 6 (2 agosto 2019): 457. http://dx.doi.org/10.15407/ujpe64.6.457.

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Abstract (sommario):

The peculiarities of the femtosecond filamentation in Kerr media has been studied using a set of time-resoling experimental techniques. These include the temporal self-compression of a laser pulse in the filamentation mode, repulsive and attractive interactions of filaments, and influence of the birefringence on the filamentation. The propagation of femtosecond laser pulses at the 1550-nm wavelength in c-Si is studied for the first time using methods of time-resolved transmission microscopy. The nonlinear widening of the pulse spectrum due to the Kerr- and plasma-caused self-phase modulation is recorded.

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LAM, Y. C., D. V. TRAN e H. Y. ZHENG. "A study of substrate temperature distribution during ultrashort laser ablation of bulk copper". Laser and Particle Beams 25, n. 1 (28 febbraio 2007): 155–59. http://dx.doi.org/10.1017/s0263034607070206.

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Abstract (sommario):

With the aid of an infrared thermograph technique, we directly observed the temperature variation across a bulk copper specimen as it was being ablated by multiple femtosecond laser pulses. Combining the experimental results with simulations, we quantified the deposited thermal power into the copper specimen during the femtosecond laser ablation process. A substantial amount of thermal power (more than 50%) was deposited in the copper specimen, implying that thermal effect can be significant in femtosecond laser materials processing in spite of its ultrashort pulse duration.

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