Seed Pulse Energy Research Articles

Stimulated Raman scattering of a broadband chirped Ti:sapphire laser pulse in calcite seeded by a narrowband nanosecond Nd:YAG laser pulse

Stimulated Raman Scattering (SRS), pumped by a broadband (i.e., compared to the bandwidth of the material excitation) chirped 50-ps pulse, with Stokes seeding by a 20-ns narrowband pulse, is experimentally and theoretically investigated. In the experiments, a femtosecond-class 0.95 μm Ti:sapphire laser system and a Q-switched 1.064 μm Nd:YAG laser were used for pumping and seeding SRS in a calcite (CaCO3) crystal. This material was chosen because its Raman resonance frequency (∼1089 cm−1) is near to the frequency difference between the pump and seed radiation. It is shown that, despite a narrowband seed, the generated Stokes pulse spectrum mimics the pump pulse spectral width. The observed SRS conversion efficiency saturates at 40%, with a weak dependence on the seed pulse energy and on the detuning of the pump-seed frequency from the Raman resonance. Theoretical modeling confirms the observed effects and permits prediction of the characteristics of the investigated system as its parameters are varied.

Ho:YLF regenerative amplifier delivering 22 mJ, 2.0 ps pulses at a 1 kHz repetition rate.

We report on a high-energy, few-ps, continuous-wave pumped Ho:YLF regenerative amplifier (RA) operating in a chirped-pulse amplification arrangement. A three-stage optical parametric amplifier serves as versatile seed source emitting broadband pulses centered at 2050 nm. It provides seed pulses with 4 µJ energy within the Ho:YLF amplification bandwidth centered at 2051 nm. Thanks to the high seed pulse energy, bifurcation instabilities are mitigated and gain narrowing is reduced for such a high-gain Ho-doped RA operating at few kHz repetition rate. At 1 kHz the Ho:YLF RA emits 22.5 mJ energy pulses with a compressed pulse duration of 2.0 ps in the stable single-pulse regime. The water cooled RA features a high extraction efficiency of 31% and exhibits a remarkable stability of 0.11% rms. Doubling the repetition rate to 2 kHz, RA pulse energy reaches 15 mJ. The demonstrated 10 GW peak power at 1 kHz and the 30 W average power at 2 kHz are the highest values reported to date for few-ps RAs operating at 2 µm wavelength.

Time-resolved VUV ARPES at 10.8 eV photon energy and MHz repetition rate

The quest for mapping the femtosecond dynamics of the electronic band structure of complex materials over their full first Brillouin zone is pushing the development of schemes to efficiently generate ultrashort photon pulses in the VUV energy range. At present, the critical aspect in time- and angle-resolved photoelectron spectroscopy (TR-ARPES) is to combine a high photon energy with high photoemission count rates and a narrow pulse-bandwidth, necessary to achieve high energy resolution, while preserving a good time resolution and mitigating space-charge effects. Here we describe a novel approach to produce light pulses at 10.8 eV, combining high repetition rate operation (1–4 MHz), high energy resolution (∼26 meV) and space-charge free operation, with a time-resolution of ∼700 fs. These results have been achieved by generating the ninth harmonic of a Yb fiber laser, through a phase-matched process of third harmonic generation in Xenon of the laser third harmonic. The full up-conversion process is driven by a seed pulse energy as low as 10 μJ, hence is easily scalable to multi-MHz operation. This source opens the way to TR-ARPES experiments for the investigation of the electron dynamics over the full first Brillouin zone of most complex materials, with unprecedented energy and momentum resolutions and high count rates. The performances of the setup are tested by TR-ARPES on the topological insulator Bi2Se3.

640-nm Pr:YLF regenerative amplifier seeded by gain-switched laser diode pulses.

We demonstrated the regenerative amplification of picosecond laser pulses generated by a gain-switched laser diode at 640 nm with a Pr:YLF crystal that was continuously pumped by a multimode blue laser diode. A 0.7-pJ seed pulse energy sufficiently suppressed the self-oscillation in the amplifier. The amplified pulse energy reached 33 µJ at a repetition rate of 10 kHz. The spatial beam quality was nearly TEM00. We also demonstrated second- and third-harmonic generation and obtained 320- and 213-nm pulse energies of 18 and 0.83 µJ at 10 kHz.

Supercontinuum Generation From a Thulium Ultrafast Fiber Laser in a High NA Silica Fiber

A broadband supercontinuum is generated from a thulium ultrafast soliton fiber laser in a high numerical aperture silica fiber with low nJ seed pulse energies. Amplification of a thulium based ultrafast soliton ring fiber laser in two customized thulium doped fiber amplifiers provides pulses varying in energy between 1.8 nJ and 13.5 nJ. Coupling these seed pulses into a high numerical aperture silica fiber UHNA 7 of varying length, a systematic study of the impact of pulse energy, pulse duration and nonlinear fiber length is conducted. Based on the normal dispersion, self-phase modulation dominates for lower pump power values and results in a symmetric spectral broadening process. For higher pulse energies, four-wave mixing and Raman scattering contribute to a strong red-shift of the spectrum beyond 2.3 μm. For a fiber length of 20 m of UHNA 7, a broadband supercontinuum spanning from 1.7 μm to 2.33 μm is generated with a 20 dB spectral bandwidth of 502 nm with an output pulse energy of 4.4 nJ, corresponding to an output power of 92 mW. This represents a low seed energy threshold for efficient flat supercontinuum generation at infrared wavelengths.

Advantages to a diverging Raman amplifier

The plasma Raman instability can efficiently compress a nanosecond long high-power laser pulse to sub-picosecond duration. Although, many authors envisaged a converging beam geometry for Raman amplification, here we propose the exact opposite geometry; the amplification should start at the intense focus of the seed. We generalise the coupled laser envelope equations to include this non-collimated case. The new geometry completely eradicates the usual trailing secondary peaks of the output pulse, which typically lower the efficiency by half. It also reduces, by orders of magnitude, the initial seed pulse energy required for efficient operation. As in the collimated case, the evolution is self similar, although the temporal pulse envelope is different. A two-dimensional particle-in-cell simulation demonstrates efficient amplification of a diverging seed with only 0.3 mJ energy. The pulse has no secondary peaks and almost constant intensity as it amplifies and diverges.

Megahertz-level, high-power picosecond Nd:LuVO4 regenerative amplifier free of period doubling.

We report on a high repetition rate, high-power picosecond Nd:LuVO4 regenerative amplifier. Period doubling caused energy instability was eliminated at megahertz-level repetition rate with the modified seeding source. A multi-pass cell was used to improve the seed pulse energy to achieve complete suppression of the onset of bifurcation. At a maximum repetition rate of 1.43 MHz, the system produced 7.0-ps-long pulses with an average output power of 25.1 W, corresponding to a pulse energy of 17.6 μJ. At 100 kHz, the pulse energy increased to 205 μJ with an average power of 20.5 W. Moreover, the injected pulses with pulse duration of 5.1 ps broadened to 8.9 ps because of gain narrowing in the amplifier.

Backward Lasing of Air plasma pumped by Circularly polarized femtosecond pulses for the saKe of remote sensing (BLACK).

Recently, S. Mitryukovskiy et al. presented experimental evidence showing that backward Amplified Spontaneous Emission (ASE) at 337 nm can be obtained from plasma filaments in nitrogen gas pumped by circularly polarized 800 nm femtosecond pulses (Opt. Express, 22, 12750 (2014)). Here, we report that a seed pulse injected in the backward direction can be amplified by ~200 times inside this plasma amplifier. The amplified 337 nm radiation can be either linearly or circularly polarized, dictated by the seeding pulse, which is distinct from the non-polarized nature of the ASE. We performed comprehensive measurements of the spatial profile, optical gain dynamics, and seed pulse energy dependence of this amplification process. These measurements allow us to deduce the pulse duration of the ASE and the amplified 337 nm radiation as well as the corresponding laser intensity inside the plasma amplifier. It indicates that the amplification is largely in the unsaturated regime and that further improvement of laser energy is possible. Moreover, we observed optical gain in plasma created in ambient air. This represents an important step towards future applications exploiting backward lasing for remote atmospheric sensing.

Two-stage optical parametric chirped-pulse amplifier using sub-nanosecond pump pulse generated by stimulated Brillouin scattering compression

We demonstrate optical parametric chirped-pulse amplification (OPCPA) based on two-beam pumping, using sub-nanosecond pulses generated by stimulated Brillouin scattering compression. Seed pulse energy, duration, and center wavelength were 5 nJ, 220 ps, and ∼1065 nm, respectively. The 532 nm pulse from a Q-switched Nd:YAG laser was compressed to ∼400 ps in heavy fluorocarbon FC-40 liquid. Stacking of two time-delayed pump pulses reduced the amplifier gain fluctuation. Using a walk-off-compensated two-stage OPCPA at a pump energy of 34 mJ, a total gain of 1.6 × 105 was obtained, yielding an output energy of 0.8 mJ. The amplified chirped pulse was compressed to 97 fs.

Investigation of the high-temporal contrast seed pulse amplification in optical parametric chirped pulse amplifier

We theoretically and experimentally investigate the amplification of a high-temporal contrast seed pulse in an optical parametric chirped pulse amplifier. The amplified and compressed signal pulse contrast can be improved by using large seed pulse energies. And the theory model is modified for considering the seed pulse contrast and compressed pulse duration. From the modified model the calculated results agree with the experimental results better.

Modeling and optimization of tapered-diode pumped Cr:LiCAF regenerative amplifiers

We present a numerical study, which investigates the potential of diode pumped Cr:LiCAF regenerative amplifiers in detail. Special attention has been given to relevant material properties of the gain media, like the Auger energy transfer upconversion (ETU) process, to utilize the full potential of the material and to develop guidelines in choosing optimal material properties like chromium doping concentration and length. Moreover, importance of pulsed pumping, rather than continuous-wave (cw) pumping, in obtaining higher small signal gain values is discussed in detail. Effects of pump power, cavity losses, excited-state absorption, seed pulse energy, optical damage and ETU on obtainable pulse energies will also be presented. The modeling results have shown that, Cr:LiCAF regenerative amplifiers pumped by two 675nm state-of-the-art 1-W tapered diodes have the potential to produce 50-fs long pulses around 800nm with 70μJ pulse energy and 1.4GW peak power at repetition rates up to 5kHz. Moreover, a 20-W diode pumped Cr:LiCAF amplifier has the potential to produce pulse energies of 1.1mJ and peak powers of 20GW. Expected optical-to-optical conversion efficiencies of the systems are about 30%. These results demonstrate that, with ongoing progress in laser diode technology, low-cost and efficient Cr:Colquiriite amplifiers has the potential to replace the expensive Ti:Sapphire technology in the future.

Enhancement of Amplified Spontaneous Emission Contrast With a Novel Front-End Based on NOPA and SHG Processes

Employing a novel front-end based on femtosecond noncollinear optical-parametric amplification and second-harmonic generation processes in a Ti:sapphire chirped pulse amplification laser system, we first demonstrate the efficient enhancement of amplified spontaneous emission (ASE) contrast. Cleaned seed pulses of 100-μJ energy generated by the front-end are amplified to 0.75 J before compressor. After compression and under pulse peak power of 7 TW, the ASE contrast is promoted from original ~ 108 to ~ 1011. The experimental results for nanometer film target interactions also demonstrate the improvement of the contrast. Finally, the evolution of the ASE contrast under different seed pulse energy is demonstrated experimentally, which can be used to design the higher power laser with higher ASE contrast.

A 12 mJ 11 ns spectrally narrow fiber amplifier with a pulsed pump

We report on the fiber-based amplification of a flash lamp pumpedQ-switched Nd:YAG laser. At a repetition rate of 10 Hz and spectrum widthof 0.1 nm, an output single pulse energy of up to 12 mJ is generated in a95 µm core Yb-doped large mode area fiber with a seed pulse energy of 0.75 mJ and pulseduration of 11 ns. No stimulated Brillouin scattering, stimulated Raman scattering orsaturation are observed. Furthermore, higher pulse energies will be achieved with higherpump powers.

Amplified spontaneous emission contrast of CPA laser

The influence on the level of amplified spontaneous emission (ASE) contrast resulting from the different seed pulse energies has been experimentally studied in a 10-TW-level femtosecond Ti:sapphire chirped pulse amplification laser. It is found that, with the seed pulse energy increasing, the ASE pedestal is suppressed more efficiently, and the ASE contrast is improved with a saturable tendency. The measurement of ~2×10-8 ASE contrast in the range of more than 50 ps before the main pulse is achieved in the laser.

Bifurcation suppression for stability improvement in Nd:YVO_4 regenerative amplifier

Continuously pumped regenerative amplifiers are subject to energy instability at high pulse repetition rates due to period doubling bifurcation. Theoretical and experimental data are presented, in order to differentiate and understand instability effects in Nd:YVO4 regenerative amplifier, and possible techniques for performance optimization are analyzed. An increase in the seed pulse energy is demonstrated to improve amplification dynamics. Addition of a preamplifier is shown as an efficient way to achieve seed energy high enough to provide stable operation at repetition rates up to 200 kHz with average output power near the theoretical limit.

Carrier-envelope phase stabilized 5.6fs, 1.2mJ pulses

The authors report the generation of 1.2mJ pulses with a duration of 5.6fs from a neon filled hollow-core fiber seeded with carrier-envelope phase stabilized 2.2mJ, 25fs pulses. The carrier-envelope phase after the fiber was measured by a second, out-loop f-to-2f interferometer. With seed pulse power locked, the carrier-envelope phase of the two-cycle pulses is controlled to a standard deviation of 370mrad. The peak power of the carrier-envelope phase stabilized pulses, 0.2TW, is twice that previously generated. The significance of seed pulse energy stability for carrier-envelope phase stabilization of few-cycle laser pulses is demonstrated.

Spectral filtering in a diode-pumped Nd:YLF regenerative amplifier using a volume Bragg grating

Instrument-limited suppression of out-of-band Amplified Spontaneous Emission (ASE) is demonstrated in a Nd:YLF Diode-Pumped Regenerative Amplifier (DPRA) using a Volume Bragg Grating (VBG) as a spectrally selective reflective element. A VBG with 99.4% diffraction efficiency and 230-pm-FWHM reflection bandwidth produced a 43-pm- FWHM output spectral width in an unseeded DPRA compared to 150-pm FWHM in the same DPRA with no VBG. Instrument-limited ASE suppression is even observed when the DPRA seed pulse energy approaches the ASE background.

High-dynamic-range temporal measurements ofshort pulses amplified by OPCPA

We report on the first experimental measurement of high-dynamic-range pulse contrast of compressed optical parametric chirped-pulse-amplification (OPCPA) pulses on the picosecond scale. The measured -80-dB OPCPA contrast at 1054 nm agrees well with theoretical predictions and exceeds the estimated and measured levels for comparable amplification in a Ti:sapphire regenerative amplifier by approximately 10 dB. A key to achieving better contrast with OPCPA is the simpler experimental setup that promotes more-efficient coupling of seed pulse energy into the amplification system.

Investigation of the superfluorescence and signal amplification in an ultrabroadband multiterawatt optical parametric chirped pulse amplifier system

We report on theoretical and experimental investigation of the signal and superfluorescence amplification in a 7 TW optical parametric chirped pulse amplifier (OPCPA) system. We demonstrate that the compressed pulse contrast ratio can be improved by using larger seed pulse energies and by careful adjustment of the pump intensity in each amplification stage. Comparison of the measured amplified signal and superfluorescence energies yielded good agreement between calculations and experiments.

Characteristics of a stable, injection Q-switched Nd:phosphate glass regenerative amplifier for a chirped pulse amplification based Table Top Terawatt laser system

A flash lamp pumped, injection Q-switched, cavity dumped Nd:phosphate glass regenerative amplifier has been designed, set up and characterized for an Nd:glass Table Top Terawatt laser system. The amplifier gain, output energy stability, amplified spontaneous emission (ASE) level, amplification time, and output pulse spectrum have been measured for different seed pulse energies and pump levels. The amplifier provides an overall gain of 3 × 10 7 in 61 round trips at an electrical pump energy of 300 J. Stable amplification has been simulated and demonstrated. The output energy fluctuations are found to reduce by a factor of 10 by ejecting the amplified pulse with a delay of five round trips after the fluence has built up to its peak level. The experimental results are found to be consistent with a theoretical model of the regenerative amplifier. The ASE intensity has been estimated using measured dependence of amplification time with respect to different seed pulse energies.