Method of aligning a four-grating compressor for the petawatt-class PEARL-X laser system

Abstract

We present a method of aligning a four-grating compressor of optical pulses developed for the multipetawatt OPCPA laser complex PEARL-X under construction at the Institute of Applied Physics of the Russian Academy of Sciences (IAP RAS). The method was successfully used in the compressor of the petawatt laser system FEMTA. The operating planes and the direction of grating grooves were aligned parallel to the vertical axis of rotation by means of silica glass alignment cubes situated on top of the diffraction gratings. Fine alignment of compressor gratings located opposite each other was done by movable mirrors which enabled observing far field images of two beams: mirror-reflected from one grating and reflected from the other grating.Successful operation of high-power laser systems based on the chirped pulse amplification (CPA) and the optical parametric chirped pulse amplification (ОРСРА) is impossible without perfect matching of dispersion characteristics of stretchers and compressors (see the review [1] and references therein). Improvement of alignment methods allows advancing to regions of shorter pulses and higher laser radiation power.In practice, however, fine alignment of compressor scheme faces the greatest difficulties to overcome which original techniques and know-how are needed. After alignment, the output radiation of the compressor and, hence, of the laser system as a whole must have minimal pulse duration, uniform distribution of duration over the beam, and high intensity contrast. The radiation must be collimated and free from amplitude front tilt and angular chirp [2].Pulses with a peak power of 0.56 PW [3] were generated at IAP RAS on the subpetawatt laser complex PEARL (PEtawatt pARametric Laser) based on the ОРСРА with frequency conversion in a nonlinear DKDP crystal [4]. The original hybrid prism-grating stretcher of this system [5] and the compressor [6] with a two-grating scheme matched to the fourth-order phase dispersion inclusive.To obtain the petawatt power level, the fourth parametric amplification cascade was added. The new laser complex FEMTA was implemented at the Russian Federal Nuclear Center (RFNC-VNIIEF) in cooperation with IAP RAS. A four-grating chirped pulse compressor was developed and built for the FEMTA facility, where pulses with a duration of 70 fs and peak power of ~ 1 PW were obtained [7]. An analogous compressor based on four diffraction gratings was created for the multipetawatt OPCPA complex PEARL-X. The angle of incidence of the input radiation with central wavelength of 910 nm on the first compressor grating was 43.13˚. According to the calculations, with this angle and the distance between the gratings of 133.75 cm on the normal, the compressor will compress a 0.5 ns chirped Gaussian pulse to a duration of 37 fs (FWHM).The developed alignment techniques for the four-grating compressor are addressed in this work. The schematic of the four-grating compressor for petawatt power radiation with alignment system is shown in fig. 1. The compressor was housed in a vacuum ...