Surface-reflection-initiated pulse-contrast degradation in an optical parametric chirped-pulse amplifier

Abstract

We study a novel mechanism of pre-pulse generation in an optical parametric chirped-pulse amplification (OPCPA) system through an analytical approach together with numerical simulations. The acquired pre-pulses are initiated from the surface-reflection-induced modulation of the seed spectrum and occur as a consequence of high-order distortion of such modulated spectrum due to the instantaneous gain saturation effect. We demonstrate that the intensities of pre-pulses increase quadratically with the initial temporal modulation-depth of the stretched signal pulse as well as the conversion efficiency prior to substantial pump-depletion. Explicit formulas for estimating the contrast limit due to surface reflections are present. We also discuss the impact of group-velocity mismatch on the pre-pulse generation. The results of this work may deepen our cognition on the complexity of the pulse-contrast problem in OPCPA systems.

Output temporal contrast simulation of a large aperture high power short pulse laser system

“…Figure 3(b) shows the temporal contrast degradation by different types of wavefront deviations. If there is no wavefront deviation, the temporal contrast will be better than 10 9 . Comparing the blue line (PV = 0.5λ) with the green line (PV = 0.1λ) in the same spatial frequency range (the same minimum spatial period T is 40 mm, which means that the same maximum spatial frequency is 0.025 mm −1 ), the wavefront deviation with larger PV value will cause 4 P. Zhu et al more severe temporal contrast degradation and in this spatial frequency range the temporal contrast will be two orders of magnitude worse than that of the ideal situation.…”

“…The European Extreme Light Infrastructure (ELI) has designed a 25 PW, 10 25 W cm −2 single laser beamline (ILE) [2] , in which the high temporal contrast required by pre-plasma-free interactions [3] will be one of the major challenges. Various factors resulting in temporal contrast degradation have been analyzed and verified, such as gain saturation [4] , asymmetric spectral clipping [5] , self-phase modulation [6] , amplified spontaneous emission (ASE) in the CPA system [7] and pump distortion-induced noise (PDN) [8] , surface-reflection-initiated pre-pulses [9] and parametric fluorescence (PF) [10] in the OPCPA system, etc.…”

Analysis of temporal contrast degradation due to wave front deviation in large aperture ultra-short pulse focusing system

“…A design of 25PW, 10 25 W/cm 2 single laser beam line has been proposed for European Extreme Light Infrastructure (ELI) 2 , in which high temporal contrast requested by pre-plasma-free interaction 3 would be one of the major challenges. Various limiting characteristics of temporal contrast have been analyzed, such as gain saturation 4 , asymmetric spectral clipping 5 , self-phase modulation 6 , amplified spontaneous emission (ASE) in CPA system 7 and pump distortion-induced noise (PDN) 8 , surface-reflectioninitiated pre-pulses 9 and parametric fluorescence (PF) 10 in OPCPA system, etc. High-energy laser systems usually have large beam diameters with relatively low energy density on optical elements due to the limited damage threshold problem, and large diameter laser systems have the inherent wave front deviation.…”

Noise filtering in parametric amplification by dressing the seed beam with spatial chirp

“…There are mainly three kinds of noises produced in parametric amplifiers, including parametric super-fluorescence (PSF) [14,15], pump distortion-induced noise (PDN) [16,17], and surface-reflection-initiated pre-pulses (SRP) [18]. These noises could degrade the contrast to lower than 10 6 .…”

“…Such ASE noise was assumed as a partially correlated Gaussian white noise with a coherent time of 0.1 ps [17]; (2) The SRP noise was studied via adding an initial postpulse into the seed with an intensity ratio of 10 −3 and time delay of 5 ps. Several prepulses, each carrying slightly different wavelengths, were produced due to the nonlinear distortion of the modulated signal spectrum resulting from the beating between the main pulse and postpulse [18,25]. The results, shown in Figs.…”