Generation of high contrast and high spatial quality idler from a low-gain optical parametric amplifier

Abstract

The temporal contrast of a regeneratively amplified, sub-picosecond pulse is enhanced employing a lowgain optical parametric amplification stage self-pumped by the second-harmonic of the pulse. Through careful characterization of the two related non-linear processes and optimization of the non-collinear geometry, a robust high-contrast idler pulse has been generated, with excellent spatial quality in both the near and far field. The overall energy conversion efficiency exceeds 14%, with 33% intensity conversion efficiency. The temporal cleaning is implemented without any bandwidth losses or spectral shift and produces approximately 20% temporal shortening. These experimental findings are in excellent agreement with numerical calculations. Exciting and rapidly developing investigations of lasermatter interactions at relativistic laser intensities have been enabled by the development of chirped-pulse amplification (CPA) techniques [1]. For these kind of interactions the temporal contrast of the laser pulse is one of the key parameters, since prepulses and pedestals can damage or deform the target before the arrival of the main pulse [2,3]. A suitably high contrast for some applications cannot be achieved from a regenerative pre-amplifier because even a very small pre-pulse can be amplified to a level sufficient to pre-ionize the target. In addition, the amplified spontaneous emission (ASE) from regenerative amplifiers can form a long pedestal around the main pulse, contributing to the degradation of the temporal contrast. Therefore, the development of laser technologies enabling ever growing intensities has been accompanied by the development of many techniques [4][5][6][7][8][9][10][11][12] for enhancing the temporal contrast.Short pulse, low gain optical parametric amplification (OPA) is one of the most efficient contrast enhancement techniques that can work at the front end of a high power laser system. Pumping an OPA with a sufficiently short pump pulse, typically shorter than 1 ps, ensures that the pump overlaps only with the main signal pulse, leaving discrete pre-pulses and the majority of the ASE pedestal outside the amplification window. This leads to enhancement of the temporal contrast of the signal by a factor equivalent to the gain factor [12]. Generating the pump pulse of the OPA by frequency doubling a part of the input pulse and using the idler rather than the signal can provide an extreme contrast enhancement that can reach up to the third power of the input contrast [9]. This theoretical prediction is limited only by parametric noise and scattered photons from the signal overlapping with the idler.In its simplest configuration, as previously described by R. Shah, et al. [10], the contrast enhancement system consists of a second harmonic generation (SHG) and a non-collinear OPA stage. The input pulse is split into two parts and the doubling stage converts a large part of the pulse energy into a second harmonic (SH) pulse to pump the following OPA stage, which is seeded by the rest of the input pul...

Laser Output Performance and Temporal Quality Enhancement at the J-KAREN-P Petawatt Laser Facility

“…The femtosecond optical parametric amplifier (fs-OPA) based on the utilization of the idler pulse rather than the signal pulse was proposed and investigated. The fs-OPA with the idler pulse has been evaluated only for the Nd:glass laser system and there have been only a limited number of reports [38][39][40]. The use of the fs-OPA with the idler pulse in a petawatt-class high-intensity Ti:sapphire laser system has not been studied, to our knowledge.…”

Single shot complete characterization of femtosecond laser pulses employing self-phase modulation

“…The spectrum of the resulting pulse can be found by implementing Fourier transformation on equation (5). According to equation ( 5), the nonlinear phase modulation encountered by the pulse depends on the intensity level and the temporal profile of the pulse.…”

“…In addition, laser pulses have been widely used in medicine, industry, spectroscopy, and other applications, e.g. [1][2][3][4][5]. A large number of these applications, especially those using ultra-short pulses, cannot be performed, or the results cannot be explained, without a complete knowledge of the profile of the pulse.…”

High-performance seed pulses for multi-petawatt laser

“…Several methods have been proposed so far to generate high contrast pulses such as noncollinear optical parametric amplification (OPA) [6], cross-polarization generation (XPW) [7], and single stage four-wave mixing (FWM) [8]. However, OPA needs precise spatial and temporal synchronization while the whole setup is complex.…”