RESUMEN
Post-compression can effectively further improve the peak power of laser pulses by shortening the pulse duration. Which has been investigated in various ranges of energy and central wavelength. However, the spatial intensity profile of high-peak-power laser pulses is generally inhomogeneous due to pump lasers, imperfect optical components, and dust in the optical layout. In post-compression, the B-integral is proportional to intensity, and wavefront distortions are induced in the spectral broadening stage, leading to a decrease in focusing intensity. Moreover, the beam intensity may be strongly modulated and beam inhomogeneity will be intensified in this process, causing damage to optical components and limiting the achievement of high peak power enhancement. In this study, to address these challenges, the laser pulse is first smoothed by introducing spatial dispersion using prism pairs or asymmetric four-grating compressors, and then the smoothed pulse is used for post-compression. The simulation results indicate that this method can effectively remove hot spots from laser pulses and maintain high peak power enhancement in post-compression.
RESUMEN
The temporal contrast of high-peak-power lasers is usually limited by pre-pulses, which are generally produced by post-pulses due to the nonlinearity of the active medium. The reason for the conversion between pre-pulse and post-pulse is now well known, but the mechanisms for the delay-shift and asymmetric broadening of the newly generated pre-pulse are not yet clear. In this work, a novel, to the best of our knowledge, numerical model combining the nonlinear Schrödinger equation and the Frantz-Nodvik equation is proposed to investigate the underlying mechanisms for the "distortion" of the pre-pulse. Numerical results show that the gain characteristics of Ti:sapphire amplifiers can only make a minor change on the temporal profile of the pre-pulse, but the high-order dispersion is the main cause for the delay-shift and asymmetric broadening of the pre-pulse, and the effects are more significant for the initial post-pulse with a relatively larger delay.
RESUMEN
In this paper, we report that the angular dispersion of the output pulses in a nonlinear process can be efficiently compensated by using a cascaded prism(s) and short hollow-core fiber (HCF) configuration. Here, the prism(s) is used to suppress the angular dispersion and transform it into spatial chirp, while the HCF is used for removing this spatial chirp and the residual angular dispersion, which can also significantly improve the beam quality. The feasibility of this novel method is numerically and experimentally investigated with the ultra-broadband idler pulses centered at 1250 nm wavelength and generated by an LBO crystal based non-collinear optical parametric amplifier. The proof-of-principle experiment shows that the angular dispersion can be effectively removed and ultra-broadband idler pulses with good spectral quality and spatial profile can be obtained. The total transmission efficiency in the experiment is around 67% and the measured M x2 and M y2 can reach 1.12 and 1.04, respectively. To the best of our knowledge, this is the first reported ultra-broadband angular dispersion compensation scheme combining prism(s) and HCF, which can remarkably eliminate the angular dispersion while simultaneously possesses high efficiency, good spectral and beam spatial quality.
RESUMEN
In this paper, we report that the conversion efficiency and spectrum of femtosecond optical parametric amplification (fs-OPA) can be significantly enhanced by employing a compact cascaded femtosecond OPA (CF-OPA) scheme with the self-compensation of the temporal walk-off between two nonlinear gain media. Correspondingly, the gain related temporal contrast can also be improved. The feasibility of the CF-OPA method using three cascaded BBO crystals is numerically and experimentally analyzed. Moreover, by replacing the conventional fs-OPA with the CF-OPA and optimizing the design, the performance of a nonlinear temporal filter combining cross-polarized wave generation and fs-OPA is comprehensively improved. The experimental results demonstrate the superiority of the CF-OPA scheme, which can generate high-performance cleaned pulses at 1 kHz repetition rate with energy of 340µJ, energy fluctuation below 0.9% (RMS), spectral width of 97 nm (FWHM), Fourier-transform-limited pulse width of 12 fs and temporal contrast better than 10-12. To the best of our knowledge, this is the first reported temporal walk-off self-compensated quasi-collinear CF-OPA geometry adopting three cascaded BBO crystals, which can be easily generalized to other wavelengths or nonlinear crystals. The above nonlinear temporal filter with a CF-OPA scheme has the rarest comprehensive parameters, which can provide excellent seed pulses for PW and 10 PW class femtosecond laser systems.