Showing papers on "Femtosecond pulse shaping published in 2017"
TL;DR: In this article, a nonlinear optical loop mirror with all polarization-maintaining fibers is used for robust mode-locked femtosecond (F2F) fiber laser.
Abstract: We report on a novel architecture for robust mode-locked femtosecond fiber lasers using a nonlinear optical loop mirror with all polarization-maintaining fibers. Due to a nonreciprocal phase shift, the loop mirror can be operated in a compact and efficient reflection mode, offering the possibility to reach high repetition rates and easy implementation of tuning elements. In particular, longitudinal mode spacing and carrier-envelope offset frequency may be controlled in order to operate the laser as an optical frequency comb. We demonstrate femtosecond pulse generation at three different wavelengths (1030, 1565, and 2050 nm) using Ytterbium, Erbium, and co-doped Thulium–Holmium as gain media, respectively. Robust operation is achieved for a wide range of parameters, including repetition rates from 10 to 250 MHz.
205 citations
TL;DR: The results show that this recently introduced compression scheme for peak powers above the threshold for catastrophic self-focusing can be scaled to smaller pulse energies and can achieve a larger compression factor than previously reported.
Abstract: We demonstrate nonlinear pulse compression by multi-pass cell spectral broadening (MPCSB) from 860 fs to 115 fs with compressed pulse energy of 7.5 µJ, average power of 300 W and close to diffraction-limited beam quality. The transmission of the compression unit is >90%. The results show that this recently introduced compression scheme for peak powers above the threshold for catastrophic self-focusing can be scaled to smaller pulse energies and can achieve a larger compression factor than previously reported. Good homogeneity of the spectral broadening across the beam profile is verified, which distinguishes MPCSB among other bulk compression schemes.
93 citations
TL;DR: In this article, the experimental demonstration of single-spike hard X-ray free-electron laser pulses starting from noise with multi-eV bandwidth was reported. But the experimental performance was limited by the fact that the beam length was less than 1 fs full width at half-maximum.
Abstract: In this letter, we report the experimental demonstration of single-spike hard-X-ray free-electron laser pulses starting from noise with multi-eV bandwidth. This is accomplished by shaping a low-charge electron beam with a slotted emittance spoiler and by adjusting the transport optics to optimize the beam-shaping accuracy. Based on elementary free-electron laser scaling laws, we estimate the pulse duration to be less than 1 fs full-width at half-maximum.
64 citations
TL;DR: It is demonstrated that energetic femtosecond pulses tunable from 1.3 to 1.7 µm can be achieved using self-phase modulation enabled spectral broadening followed by spectral lobe filtering using a home-built 5-W Er-fiber laser system.
Abstract: We demonstrate that energetic femtosecond pulses tunable from 1.3 to 1.7 µm can be achieved using self-phase modulation enabled spectral broadening followed by spectral lobe filtering. Based on a home-built 5-W Er-fiber laser system operating at 31-MHz repetition rate, we obtain femtosecond pulses that can be continuously tuned from 1.3 to 1.7 µm with >4.5 nJ pulse energy. We further optimize the spectral broadening process using a fiber with larger mode area and scale up the pulse energy to >10 nJ; the resulting pulse duration is as short as ~50 fs. Such a widely tunable, energetic femtosecond source is well suited for driving a laser scanning microscope to perform deep tissue multiphoton microscopy.
59 citations
TL;DR: In this paper, a simple method to form approximately unipolar halfcycle optical pulses via reflection of a single-cycle optical pulse from a thin flat metallic or dielectric layer was proposed.
Abstract: We propose a strikingly simple method to form approximately unipolar half-cycle optical pulses via reflection of a single-cycle optical pulse from a thin flat metallic or dielectric layer. Unipolar pulses in reflection arise due to specifics of one-dimensional pulse propagation. Namely, we show that the field emitted by the layer is proportional to the velocity of the oscillating charges in the medium, instead of their acceleration. Besides, the oscillation velocity of the charges can be forced to keep a constant sign throughout the pulse duration. That is, reflection of ultrashort pulses from broad-area layers with nanometer-scale thickness can be very different from the common reflection in the case of longer pulses and thicker layers. This suggests a possibility of unusual transformations of few-cycle light pulses in completely linear optical systems.
51 citations
TL;DR: A simple Fe3O4 nanoparticles (FONPs) based Q-switched fiber laser that is able to generate stable nanosecond pulses with single-wavelength or multiwavelength regimes was demonstrated in this paper.
Abstract: We demonstrate a simple Fe3O4 nanoparticles (FONPs) based Q-switched fiber laser that is able to generate stable nanosecond pulses with single-wavelength or multiwavelength regimes. In the single-wavelength lasing scheme, the fiber laser generates 613-ns pulse with average output power of 41.2 mW, pulse energy of 321.3 nJ, and signal-noise-ratio of 54.4 dB. In the multiwavelength lasing scheme, stable pulse is achieved with 18-wavelength channels contained within the 3-dB bandwidth range. Our results prove that the FONPs can act as an effective Q-switch for high-energy pulse generation.
41 citations
TL;DR: Pulse compression of an 18.5 MHz repetition rate pulse train from 230 fs to sub-40 fs by nonlinear spectral broadening in a multi-pass cell and subsequent chirp removal is reported.
Abstract: We report on the pulse compression of an 18.5 MHz repetition rate pulse train from 230 fs to sub-40 fs by nonlinear spectral broadening in a multi-pass cell and subsequent chirp removal. The compressed pulse energy is $4.5~\mu \text{J}$ , which corresponds to 84 W of average power, with a compression efficiency of 88%. This recently introduced compression scheme is suitable for a large pulse energy range and for high average power. In this paper, we show that it can achieve three times shorter pulses than previously demonstrated.
37 citations
TL;DR: The obtained femtosecond vortex has an unprecedented ring-to-center intensity contrast of 36 dB measured with a near wavelength-spatial-resolution detecting device, which approaches the theoretical limit of an ideal vortex beam.
Abstract: Femtosecond optical vortices open a variety of fascinating applications, ranging from femtosecond micro–nano manipulation to vortex strong-field physics. A basic requirement for these applications is that the femtosecond vortex has a clean intensity node for capturing or trapping particles. Thus far, the generation of clean femtosecond vortices remains a challenge. Here, we report on ultraclean femtosecond vortex generation by a femtosecond mode-locked laser operating in a single high-order transverse mode. By controlling the oscillation thresholds of various-order transverse modes in a laser, a pure and mode-order-tunable femtosecond Hermite–Gaussian beam is generated from the mode-locked laser and, subsequently, is converted into the femtosecond vortex by a cylindrical lens mode converter. The obtained femtosecond vortex has an unprecedented ring-to-center intensity contrast of 36 dB measured with a near wavelength-spatial-resolution detecting device, which approaches the theoretical limit of an ideal vortex beam. This Letter may open a wide range of application prospects for femtosecond vortices and motivate novel femtosecond structured beam generation directly from mode-locked lasers.
35 citations
TL;DR: Theoretical analysis and experimental results demonstrated that the left- and right-handed circular polarization fundamental modes of the femtosecond optical pulse could be converted to the linearly polarized ±1-order optical vortex modes through the AIFG with the mode conversion efficiency of ∼95%.
Abstract: We proposed a method for generation of a femtosecond optical vortex pulse in a two-mode fiber based on an acoustically induced fiber grating (AIFG) driven by a radio frequency source. Theoretical analysis and experimental results demonstrated that the left- and right-handed circular polarization fundamental modes of the femtosecond optical pulse could be converted to the linearly polarized ±1-order optical vortex modes through the AIFG with the mode conversion efficiency of ∼95%. The off-axial interference experiment and the polarization angle-dependent intensity examination were performed to verify the topological charge and the polarization state of the femtosecond optical vortex, respectively.
34 citations
TL;DR: In this paper, the authors describe progress and results of recent work on ultrafast pulse characterization at soft and hard X-ray free-electron laser sources and report on different approaches to laser-assisted time-domain measurements.
Abstract: For the investigation of processes happening on the time scale of the motion of bound electrons, well-controlled X-ray pulses with durations in the few-femtosecond and even sub-femtosecond range are a necessary prerequisite. Novel free-electron lasers sources provide these ultrashort, high-brightness X-ray pulses, but their unique aspects open up concomitant challenges for their characterization on a suitable time scale. In this review paper we describe progress and results of recent work on ultrafast pulse characterization at soft and hard X-ray free-electron lasers. We report on different approaches to laser-assisted time-domain measurements, with specific focus on single-shot characterization of ultrashort X-ray pulses from self-amplified spontaneous emission-based and seeded free-electron lasers. The method relying on the sideband measurement of X-ray electron ionization in the presence of a dressing optical laser field is described first. When the X-ray pulse duration is shorter than half the oscillation period of the streaking field, few-femtosecond characterization becomes feasible via linear streaking spectroscopy. Finally, using terahertz fields alleviates the issue of arrival time jitter between streaking laser and X-ray pulse, but compromises the achievable temporal resolution. Possible solutions to these remaining challenges for single-shot, full time–energy characterization of X-ray free-electron laser pulses are proposed in the outlook at the end of the review.
34 citations
TL;DR: A laser system capable of generating high-energy (>270 mJ) temporally shaped pulses at 1064 nm with 0.43-ns shaping resolution that is fully programmable complex temporal shapes is reported on.
Abstract: We report on a laser system capable of generating high-energy (>270 mJ) temporally shaped pulses at 1064 nm with 0.43-ns shaping resolution. The pulses are generated by modulation of a continuous-wave seed laser and subsequent amplification by a dual-stage grazing-incidence Nd:YVO4 “bounce” amplifier and a Nd:YAG power amplifier (all quasi-continuous diode-pumped). The system produces pulses with a high-quality top-hat spatial beam profile with up to 0.6 GW of peak power and 44 W of average power, a power stability of 0.22% rms, and fully programmable complex temporal shapes.
TL;DR: In this paper, a high-energy thulium-doped all-fiber soliton laser passively mode-locked by nonlinear polarization rotation (NPR) technology is presented, generating 350 fs pulses with spectral width of 11.5 nm at 1890 nm wavelength.
Abstract: A high-energy thulium-doped all-fiber soliton laser passively mode-locked by nonlinear polarization rotation (NPR) technology is presented, generating 350 fs pulses with spectral width of 11.5 nm at 1890 nm wavelength. Kelly sidebands of the soliton spectrum are well suppressed due to the NPR effect in the fiber laser. The average output power reaches 90 mW, corresponding to the pulse energy up to 7.8 nJ and the pulse peak power of 22.3 kW, leading to the higher order soliton generation. This has been testified by the relationship between the soliton period and the cavity length. Thus, the laser can deliver high-energy ultrashort soliton pulses while the pulse shape is close to one of the fundamental solitons. We believe that this represents one of the best observations of short pulse duration as well as high pulse power coexisting in Tm-doped soliton fiber lasers.
TL;DR: This work demonstrates for the first time the efficient high-energy SBS sub-phonon lifetime pulse compression, and paves a way to the reliable generation of sub-200 ps laser pulses with Joule-level energy.
Abstract: Multi-Joule level stimulated Brillouin scattering (SBS) pulse compression below the acoustic phonon lifetime is demonstrated with a energy-scalable generator-amplifier setup Single-pass compression of pulses longer than 20τB (τB as phonon lifetime) to as short as 05τB with ~100 mJ pulse energy is realized from the generator, by choosing the focusing length to match approximately with the full length at half maximum of the input Gaussian pulses The interaction length is identified, both experimentally and numerically, as the key parameter in achieving sub-phonon lifetime pulse compression, with its main mechanism being the steepening of the Stokes pulse trailing edge via energy exchange process After combining the generator with an amplifier that involves only collimated beams and serves as energy booster, the compression of 9 ns, 2 J pulses at 532 nm into 170 ps, 13 J per pulse is achieved in water, with very good stability in both pulse energy and duration This work demonstrates for the first time the efficient high-energy SBS sub-phonon lifetime pulse compression, and paves a way to the reliable generation of sub-200 ps laser pulses with Joule-level energy
TL;DR: In this article, the dynamics of plasma and shockwave expansion during two femtosecond laser pulse ablation of fused silica are studied using a time-resolved shadowgraph imaging technique.
Abstract: The dynamics of plasma and shockwave expansion during two femtosecond laser pulse ablation of fused silica are studied using a time-resolved shadowgraph imaging technique. The experimental results reveal that during the second pulse irradiation on the crater induced by the first pulse, the expansion of the plasma and shockwave is enhanced in the longitudinal direction. The plasma model and Fresnel diffraction theory are combined to calculate the laser intensity distribution by considering the change in surface morphology and transient material properties. The theoretical results show that after the free electron density induced by the rising edge of the pulse reaches the critical density, the originally transparent surface is transformed into a transient high-reflectivity surface (metallic state). Thus, the crater with a concave-lens-like morphology can tremendously reflect and refocus the latter part of the laser pulse, leading to a strong laser field with an intensity even higher than the incident intensity. This strong refocused laser pulse results in a stronger laser-induced air breakdown and enhances the subsequent expansion of the plasma and shockwave. In addition, similar shadowgraphs are also recorded in the single-pulse ablation of a concave microlens, providing experimental evidence for the enhancement mechanism.
TL;DR: The theoretical pump-to-idler conversion efficiency reaches 27% in the DC-OPA pumped by a chirped broadband Cr2+:ZnSe/ZnS laser, enabling the generation of Terawatt-level 4–12 μm pulses with an available large-aperture ZGP.
Abstract: We present an approach for both efficient generation and amplification of 4–12 μm pulses by tailoring the phase matching of the nonlinear crystal Zinc Germanium Phosphide (ZGP) in a narrowband-pumped optical parametric chirped pulse amplifier (OPCPA) and a broadband-pumped dual-chirped optical parametric amplifier (DC-OPA), respectively. Preliminary experimental results are obtained for generating 1.8–4.2 μm super broadband spectra, which can be used to seed both the signal of the OPCPA and the pump of the DC-OPA. The theoretical pump-to-idler conversion efficiency reaches 27% in the DC-OPA pumped by a chirped broadband Cr2+:ZnSe/ZnS laser, enabling the generation of Terawatt-level 4–12 μm pulses with an available large-aperture ZGP. Furthermore, the 4–12 μm idler pulses can be compressed to sub-cycle pulses by compensating the tailored positive chirp of the idler pulses using the bulk compressor NaCl, and by indirectly controlling the higher-order idler phase through tuning the signal (2.4–4.0 μm) phase with a commercially available acousto-optic programmable dispersive filter (AOPDF). A similar approach is also described for generating high-energy 4–12 μm sub-cycle pulses via OPCPA pumped by a 2 μm Ho:YLF laser.
TL;DR: These bichromatic CEP-stable polarization-shaped ultrashort laser pulses provide a versatile class of waveforms for coherent control experiments and allow for individual spectral phase modulation of both colors.
Abstract: We apply ultrafast polarization shaping to an ultrabroadband carrier envelope phase (CEP) stable white light supercontinuum to generate polarization-tailored bichromatic laser fields of low-order frequency ratio The generation of orthogonal linearly and counter-rotating circularly polarized bichromatic fields is achieved by introducing a composite polarizer in the Fourier plane of a 4 f polarization shaper The resulting Lissajous- and propeller-type polarization profiles are characterized experimentally by cross-correlation trajectories The scheme provides full control over all bichromatic parameters and allows for individual spectral phase modulation of both colors Shaper-based CEP control and the generation of tailored bichromatic fields is demonstrated These bichromatic CEP-stable polarization-shaped ultrashort laser pulses provide a versatile class of waveforms for coherent control experiments
TL;DR: In this paper, the dielectric properties of diamond in excited state modulated by an ultrashort and intense single-cycle laser field are investigated based on the real-time time-dependent density functional theory.
Abstract: The dielectric properties of diamond in excited state modulated by an ultrashort and intense single-cycle laser field are investigated based on the real-time time-dependent density functional theory. The electron dynamics of diamond is analyzed within ultrashort time resolution. The change of dielectric properties are demonstrated by studying the effect of easily tunable laser parameters including intensity, frequency, and duration time. The extracted dielectric function shows anisotropy even in an centrosymmetric diamond when going beyond the linear response regime. We also demonstrate control of the dielectric functions by the delay time between pump and probe pulse. It is concluded that a tailored single-cycle laser field can be used to effectively manipulate the dielectric properties of wide-band gap materials.
TL;DR: A novel coherent beam combiner, capable of combining large numbers of femtosecond pulse beams using two diffractive optics, is presented, showing analytically that combining loss due to uncorrected dispersions is only a few percent for ∼200 beams with 130 fs pulses.
Abstract: A novel coherent beam combiner, capable of combining large numbers of femtosecond pulse beams using two diffractive optics, is presented. The diffractive optic pair cancels pulse front tilt, while uncorrected dispersions are minimized. An example using four beams is modeled numerically and tested experimentally, demonstrating 120 fs pulses combined without degradation of pulse width. Scaling the concept, we show analytically that combining loss due to uncorrected dispersions is only a few percent for ∼200 beams with 130 fs pulses.
TL;DR: In this article, a pair of probe and coupling laser pulses propagating in a Doppler broadened three-level cascade atomic medium were studied in a wide region of pulse duration, from micro to pico second.
TL;DR: In this paper, the authors present a numerical investigation of pulse shape evolution and pulse regime transformation in an all-normal dispersion mode-locked fiber laser and find that the pump strength and spectral filtering had great effects on the properties of the generated dissipative solitons.
Abstract: We present a numerical investigation of pulse shape evolution and pulse regime transformation in an all-normal dispersion mode-locked fiber laser. We found that the pump strength and spectral filtering had great effects on the properties of the generated dissipative solitons. The pulse had a parabolic intensity profile and linear chirp when the pump strength was large enough under certain bandwidth of the spectral filter. Such a parabolic pulse worked in the intermediate regime between the dissipative soliton and similariton; however, the pulse resembled a dissipative soliton. Pulse regime transformation will happen when the pump strength is large enough; the pulse will become multi-pulse, bound-state pulse, or noise-like pulse under different filter bandwidths and pump strengths. The results of our numerical simulations could offer a better understanding of the dynamics of all-normal dispersion mode-locked fiber lasers and also provide insight into the dissipative fiber laser systems.
TL;DR: In this paper, the authors demonstrated that few-cycle pulses can be achieved from an Er-doped fiber laser via single-stage soliton compression, where negative prechirp amplification is adopted to avoid the high-energy pulse break-up and increase the spectral width.
Abstract: We have demonstrated experimentally that few-cycle pulses can be achieved from an Er-doped fiber laser via single-stage soliton compression. Adopting negative prechirp amplification is to avoid the high-energy pulse break-up and increase the spectral width. Through optimizing the fiber length and pulse energy in different parts of the fiber laser system, the generated pulse can be as short as 22.7 fs, which is about four cycle duration at 1550 nm. The average power is up to 120 mW with the corresponding pulse energy of 2.8 nJ. Numerical simulation has been carried out to illustrate the dynamic of pulse prechirp, amplification, and compression.
TL;DR: In this article, a two-beam femtosecond coherent anti-Stokes Raman scattering was used for thermometry on CO2 for temperatures between ∼100°C and ∼600°C at a maximum pressure of 8.5 bar.
Abstract: We show that two-beam femtosecond coherent anti-Stokes Raman scattering can be effectively used for thermometry on CO2 for temperatures between ∼100 °C and ∼600 °C at a maximum pressure of 8.5 bar. The temperature measurement is based on probing the vibrationally excited states of CO2, using a ∼7 fs pump/Stokes pulse and a narrowband (∼0.3 nm) probe pulse. The temperatures can be derived from a single spectrum, obviating the need for a delay scan or a chirped probe pulse.
TL;DR: It is shown that the ultimate limitations of the MCF based ablation are the nonlinear effects induced by the pulse in the MCFs cores, which allows for focusing and scanning the pulse without requiring distal end optics and enables a smaller ablation tool.
Abstract: Ultrashort pulse ablation has become a useful tool for micromachining and biomedical surgical applications. Implementation of ultrashort pulse ablation in confined spaces has been limited by endoscopic delivery and focusing of a high peak power pulse. Here we demonstrate ultrashort pulse ablation through a thin multi-core fiber (MCF) using wavefront shaping, which allows for focusing and scanning the pulse without requiring distal end optics and enables a smaller ablation tool. The intensity necessary for ablation is significantly higher than for multiphoton imaging. We show that the ultimate limitations of the MCF based ablation are the nonlinear effects induced by the pulse in the MCFs cores. We characterize and compare the performance of two devices utilizing a different number of cores and demonstrate ultrashort pulse ablation on a thin film of gold.
TL;DR: A nonlinear pulse compression stage delivering 252 μJ, sub-50 fs-pulses at 15.4 W of average power was enabled by actively mitigating ultrashort pulse propagation effects induced by the presence of water vapor absorptions.
Abstract: The combination of high-repetition-rate ultrafast thulium-doped fiber laser systems and gas-based nonlinear pulse compression in waveguides offers promising opportunities for the development of high-performance few-cycle laser sources at 2 μm wavelength. In this Letter, we report on a nonlinear pulse compression stage delivering 252 μJ, sub-50 fs-pulses at 15.4 W of average power. This performance level was enabled by actively mitigating ultrashort pulse propagation effects induced by the presence of water vapor absorptions.
TL;DR: In this article, an energy-scaling experiment on a femtosecond infrared pulse using dual-chirped optical parametric amplification (DC-OPA) was presented.
Abstract: We present an energy-scaling experiment on a femtosecond infrared pulse using dual-chirped optical parametric amplification (DC-OPA) A total output energy exceeding 100 mJ with 36-fs pulse duration was achieved in the infrared region, which is the highest energy ever reported for an ultrafast optical parametric amplifier scheme We also discuss the generation of high-energy 15–30–THz pulses through difference frequency generation between chirped signal and idler pulses based on DC-OPA By manipulating the phase of a seed pulse in the DC-OPA system, the spectral phase of a THz pulse can be indirectly controlled precisely, which is very helpful for compressing THz pulses
TL;DR: In this article, a colliding pulse mode-locked VECSEL with a pulse duration as short as 128fs was studied, with an average power of 90mW per beam and a repetition rate of 3.27
Abstract: The passive mode locking of vertical external cavity surface emitting lasers (VECSELs) enables the generation of high brightness ultrashort pulses at high repetition rates with unmatched performance. The peak power achievable with sub-200-fs pulse duration is mostly limited by the stability of the fundamental mode-locking regime as side pulses or harmonic mode locking emerges at high pump power. Here, we study a colliding pulse mode-locked VECSEL generating a pulse duration as short as 128 fs, with an average power of 90 mW per beam and a repetition rate of 3.27 GHz. The relevant laser parameters under different pumping regimes before and after the emergence of a side pulse are then used as input parameters for the simulation of the pulse interactions in the saturable absorber. We present a new comprehensive model for the calculation of saturable losses in the saturable absorber mirror and we study the energy transfer between the two counter-propagating pulses. This study reveals how a colliding pulse scheme reduces the saturation fluence of the absorber by a factor 2.9 and suppresses the mode competition between the two counterpropagating pulses of the ring cavity.
TL;DR: In this paper, an efficient, high precision system for direct laser microstructuring using fiber laser generated bursts of picosecond pulses has been developed, where an advanced opto-mechanical system for beam deflection and sample movement, precise pulse energy control, and a custom built fiber laser with the pulse duration of 65 ps have been combined in a compact setup.
Abstract: We have developed an efficient, high precision system for direct laser microstructuring using fiber laser generated bursts of picosecond pulses. An advanced opto-mechanical system for beam deflection and sample movement, precise pulse energy control, and a custom built fiber laser with the pulse duration of 65 ps have been combined in a compact setup. The setup allows structuring of single-micrometer sized objects with a nanometer resolution of the laser beam positioning due to a combination of acousto-optical laser beam deflection and tight focusing. The precise synchronization of the fiber laser with the pulse burst repetition frequency of up to 100 kHz allowed a wide range of working parameters, including a tuneable number of pulses in each burst with the intra-burst repetition frequency of 40 MHz and delivering exactly one burst of pulses to every chosen position. We have demonstrated that tightly focused bursts of pulses significantly increase the ablation efficiency during the microstructuring of a copper layer and shorten the typical processing time compared to the single pulse per spot regime. We have used a simple short-pulse ablation model to describe our single pulse ablation data and developed an upgrade to the model to describe the ablation with bursts. Bursts of pulses also contribute to a high quality definition of structure edges and sides. The increased ablation efficiency at lower pulse energies compared to the single pulse per spot regime opens a window to utilize compact fiber lasers designed to operate at lower pulse energies, reducing the overall system complexity and size.
TL;DR: In this paper, a detailed study revealed that the picosecond pulse train ablation improved the quality of laser craters (symmetric crater walls and the absence of large redeposited droplets), which was explained by a smaller heat affected zone and suppression of melt splash.
Abstract: Picosecond pulse train and nanosecond pulse were compared for laser ablation and laser induced breakdown spectroscopy (LIBS) measurements. A detailed study revealed that the picosecond pulse train ablation improved the quality of laser craters (symmetric crater walls and the absence of large redeposited droplets), which was explained by a smaller heat affected zone and suppression of melt splash. Greater plasma dimensions and brighter plasma emission were observed by gated imaging for picosecond pulse train compared to nanosecond pulse ablation. Increased intensity of atomic and ionic lines in gated and time integrated spectra provided better signal-to-noise ratio for picosecond pulse train sampling. Higher temperature and electron density were detected during first microsecond for the plasma induced by the picosecond pulse train. Improved shot-to-shot reproducibility for atomic/ionic line intensity in the case of picosecond pulse train LIBS was explained by more effective atomization of target material in plasma and better quality of laser craters. Improved precision and limits of detections were determined for picosecond pulse train LIBS due to better reproducibility of laser sampling and increased signal-to-noise ratio.
TL;DR: The femtosecond interferograms of laser-produced plasmas obtained by the three-frame interferometer and the femtOSEcond polarimetric images obtained byThe two-frame polaro-interferometer confirm the full usefulness and correct functionality of the proposed method of synchronization.
Abstract: A system of precise pulse synchronization between a single-shot large-scale laser exploiting an acousto-optical modulator and a femtosecond high repetition rate laser is reported in this article. This opto-electronical system has been developed for synchronization of the sub-nanosecond kJ-class iodine photodissociation laser system (Prague Asterix Laser System—PALS) with the femtosecond 25-TW Ti:sapphire (Ti:Sa) laser operating at a repetition rate 1 kHz or 10 Hz depending on the required energy level of output pulses. At 1 kHz synchronization regime, a single femtosecond pulse of duration about 45 fs and a small energy less than 1 mJ are exploited as a probe beam for irradiation of a three-frame interferometer, while at 10 Hz repetition rate a single femtosecond pulse with higher energy about 7–10 mJ is exploited as a probe beam for irradiation of a two-channel polaro-interferometer. The synchronization accuracy ±100 ps between the PALS and the Ti:Sa laser pulses has been achieved in both regimes of sync...