High temporal contrast 1053 nm laser source based on optical parametric amplification and second-harmonic generation

Temporal contrast directly affects the interaction between ultraintense and ultrashort pulse lasers with matter.Seed laser sources with broad bandwidth and high temporal contrast are significant for overall temporal contrast enhancement.The technique of cascaded nonlinear processes with optical parametric amplification and second-harmonic generation is demonstrated for high temporal contrast seed source generation.Within 40 ps before the main pulse,the temporal contrast reaches over 10^(11).The pulse energy and duration of the high-contrast pulse are 112μJ and 70 fs,respectively.Considering its high beam quality and stability,this laser source can serve as a high-quality seed for Nd:glass-based ultraintense and ultrashort pulse laser facilities.

Suppression of nanosecond prepulses from regenerative amplifier and multipass amplifiers in the SULF-1PW laser

In this research,we report the latest progress in the suppression of nanosecond prepulses from regenerative amplifier and multipass amplifiers in the SULF-1PW laser.The prepulse generated from the Pockels cell(PC)in a regenerative amplifier is delay-shifted by enlarging the distance between the PC and the nearby cavity mirror,and then removed by the extra pulse pickers outside the regenerative amplifier.The prepulses arising from multipass amplifiers are also further suppressed by adopting a novel amplifier configuration and properly rotating the Ti:sapphire crystals.After the optimizations,the temporal contrast on a nanosecond time scale is promoted to be better than a contrast level of 10^(-9).This research can provide beneficial guidance for the suppression of nanosecond prepulses in the high-peak-power femtosecond laser systems.

Systematic study of spatiotemporal influences on temporal contrast in the focal region in large-aperture broadband ultrashort petawatt lasers

Temporal contrast is one of the crucial physical determinants which guarantee the successful performance of laser–matter interaction experiments. We generally reviewed the influences on the temporal contrast in three categories of noises based on the requirement by the physical mechanisms. The spatiotemporal influences on temporal contrast at the focal region of the chromatic aberration and propagation time difference introduced by large-aperture broadband spatial filters, which were spatiotemporally coupled with compression and focusing, were calculated and discussed with a practical case in SG-Ⅱ5 PW ultrashort petawatt laser. The system-wide spatiotemporal coupling existing in large-aperture broadband ultrashort petawatt lasers was proved to be one of the possible causes of temporal contrast degradation in the focal region.

Ultrahigh temporal contrast performance of the PHELIX petawatt facility

We report on the temporal contrast performance of the PHELIX facility in view of the requirements imposed by solidtarget interaction experiments. The requirement analysis for the nanosecond and picosecond temporal contrast is derived from empirical data and simple theoretical modeling, while the realization shows that using an ultrafast optical parametric amplifier and plasma mirrors enables meeting this specification.

Temporal contrast enhancement by nonlinear elliptical polarization rotation in a multi-pass cell

We demonstrate the simultaneous temporal contrast improvement and pulse compression of a Yb-doped femtosecond laser via nonlinear elliptical polarization rotation in a solid state multi-pass cell.The temporal contrast is improved to 109,while the pulse is shortened from 181 to 36 fs,corresponding to a compression factor of 5.The output beam features excellent beam quality with M^(2) values of 1.18×1.16.The total efficiency of the contrast enhancement system exceeds 50%.This technique will have wide applications in high temporal contrast ultra-intense femtosecond lasers.

How the laser beam size conditions the temporal contrast in pulse stretchers of chirped-pulse amplification lasers

In this work,we propose and verify experimentally a model that describes the concomitant influence of the beam size and optical roughness on the temporal contrast of optical pulses passing through a pulse stretcher in chirped-pulse amplification laser systems.We develop an analytical model that is capable of predicting the rising edge caused by the reflection from an optical element in a pulse stretcher,based on the power spectral density of the surface and the spatial beam profile on the surface.In an experimental campaign,we characterize the temporal contrast of a laser pulse that passed through either a folded or an unfolded stretcher design and compare these results with the analytical model.By varying the beam size for both setups,we verify that optical elements in the near-and the far-field act opposed to each with respect to the temporal contrast and that the rising edge caused by a surface benefits from a larger spatial beam size on that surface.

High-performance 800-1050 nm seed pulses based on spectral broadening and filtering for petawatt lasers

High-performance 86μJ,11.2 fs pulses with a spectrum range of 800-1050 nm are generated based on 1030 nm,190 fs Yb femtosecond pulses by using multi-plate-based spectral broadening and filtering.Taking advantage of single beam configuration,the obtained pulses have excellent power and spectral stabilities.Since the output spectrum is obtained by spectrally filtering the broadened components,the temporal contrast of the output pulses is enhanced by at least four orders of magnitude.Together with the robust and simple setup,the proposed method is expected to be a competitive option for the generation of seed pulses for 10s-100s petawatt lasers.

Ultra-broadband pulse generation via hollow-core fiber compression and frequency doubling for ultra-intense lasers

We demonstrate an ultra-broadband high temporal contrast infrared laser source based on cascaded optical parametric amplification,hollow-core fiber(HCF)and second harmonic generation processes.In this setup,the spectrum of an approximately 1.8μm laser pulse has near 1μm full bandwidth by employing an argon gas-filled HCF.Subsequently,after frequency doubling with cascaded crystals and dispersion compensation by a fused silica wedge pair,9.6 fs(~3cycles)and 150μJ pulses centered at 910 nm with full bandwidth of over 300 nm can be generated.The energy stability of the output laser pulse is excellent with 0.8%(root mean square)over 20 min,and the temporal contrast is>10^(12)at-10 ps before the main pulse.The excellent temporal and spatial characteristics and stability make this laser able to be used as a good seed source for ultra-intense and ultrafast laser systems.

A cylindricalÖffner stretcher based on ternary reflector for femtosecond petawatt-level laser system

A cylindricalÖffner stretcher based on ternary reflector(COSTER)is proposed and analyzed.Compared with the traditionalÖffner stretcher,the COSTER has no off-axis aberration in the multipass configuration,and the output laser of COSTER has lower spectral phase noise and higher temporal contrast in the far field.The COSTER is quite suitable to be used in multipetawatt laser facilities,and it might be the preferred stretcher configuration for ultrafast and ultra-intense lasers.

Millijoule ultrafast optical parametric amplification as replacement for high-gain regenerative amplifiers

We report on the development of an ultrafast optical parametric amplifier front-end for the Petawatt High Energy Laser for heavy Ion eXperiments(PHELIX)and the Petawatt ENergy-Efficient Laser for Optical Plasma Experiments(PEnELOPE)facilities.This front-end delivers broadband and stable amplification up to 1 mJ per pulse while maintaining a high beam quality.Its implementation at PHELIX allowed one to bypass the front-end amplifier,which is known to be a source of pre-pulses.With the bypass,an amplified spontaneous emission contrast of 4.9×10^(−13)and a pre-pulse contrast of 6.2×10^(−11)could be realized.Due to its high stability,high beam quality and its versatile pump amplifier,the system offers an alternative for high-gain regenerative amplifiers in the front-end of various laser systems.

Linear angular dispersion compensation of cleaned self-diffraction light with a single prism

The linear angular dispersion of a self-diffraction(SD) pulse, from a femtosecond laser pulse cleaning device, is compensated for by the use of a single prism. More than 500 μJ first-order SD pulse has a contrast of 1012, which is about five orders of magnitude improvement from the input fundamental pulse. The wings of the distribution away from the main pulse in ±1 ps are cleaned with a contrast improvement of about 107, which verifies the pulse cleaning ability of the SD process.

A route to enhanced performance for the petawatt beamlines of the Orion laser facility

The Orion laser facility at AWE provides multiple beams to target delivering synchronized pulses at both nanosecond and sub-picosecond duration.In the latter,the peak power approaches the petawatt level.This paper presents a conceptual design for potential development of these beamlines.This would deliver a significant enhancement of performance at the fundamental level.In addition,a new approach is described for the management of frequency conversion at high intensity,which may allow significantly enhanced performance at the second harmonic also.

Single-shot fourth-order autocorrelator

Temporal contrast(TC)is one of the most important parameters of an ultrahigh intense laser pulse.The third-order autocorrelator or cross correlator has been widely used in the past decades to characterize the TC of an ultraintense laser pulse.A novel and simple single-shot fourth-order autocorrelator(FOAC)to characterize the TC with higher time resolution and better pulse contrast fidelity in comparison to third-order correlators is proposed.The single-shot fourth-order autocorrelation consists of a frequency-degenerate four-wave mixing process and a sum-frequency mixing process.The proof-of-principle experiments show that a dynamic range of∼10^11 compared with the noise level,a time resolution of∼160 fs,and a time window of 65 ps can successfully be obtained using the single-shot FOAC,which is to-date the highest dynamic range with simultaneously high time resolution for single-shot TC measurement.Furthermore,the TC of a laser pulse from a petawatt laser system is successfully measured in single shot with a dynamic range of about 2×10^10 and simultaneously a time resolution of 160 fs.

Generation of high-contrast, joule-level pulses based on Nd:glass chirped pulse amplification laser

We demonstrate a high-contrast, joule-level Nd:glass laser system operating at 0.5 Hz repetition rate based on a double chirped pulse amplification(CPA) scheme. By injecting high-contrast, high-energy seed pulses into the Nd:glass CPA stage, the pulse energy is amplified to 1.9 J through two optical parametric CPA stages and two Nd:glass amplifiers. The temporal contrast of compressed pulse is measured down to the level of 10^(-8)at tens of ps, and 10^(-10) near 200 ps before the main pulse, respectively.

Accelerating ions with high-energy short laser pulses from submicrometer thick targets

Using the example of the PHELIX high-energy short pulse laser we discuss the technical preconditions to investigate ion acceleration with submicrometer thick targets. We show how the temporal contrast of this system was improved to prevent pre-ionization of such targets on the nanosecond timescale. Furthermore the influence of typical fluctuations or uncertainties of the on-target intensity on ion acceleration experiments is discussed. We report how these uncertainties were reduced by improving the assessment and control of the on-shot intensity and by optimizing the positioning of the target into the focal plane. Finally we report on experimental results showing maximum proton energies in excess of 85 MeV for ion acceleration via the target normal sheath acceleration mechanism using target thicknesses on the order of one micrometer.

Enhancement of pre-pulse and picosecond pedestal contrast of the petawatt J-KAREN-P laser

We have experimentally improved the temporal contrast of the petawatt J-KAREN-P laser facility.We have investigated how the generation of pre-pulses by post-pulses changes due to the temporal overlap between the stretched pulse and the post-pulse in a chirped-pulse amplification system.We have shown that the time at which the pre-pulse is generated by the post-pulse and its shape are related to the time difference between the stretched main pulse and the post-pulse.With this investigation,we have found and identified the origins of the pre-pulses and have demonstrated the removal of most pre-pulses by eliminating the post-pulse with wedged optics.We have also demonstrated the impact of stretcher optics on the picosecond pedestal.We have realized orders of magnitude enhancement of the pedestal by improving the optical quality of a key component in the stretcher.