Compensation of FM-to-AM conversion in high-power lasers.

ABSTRACT

FM-to-AM conversion in the ninth beam of the Shen Guang II laser system with sinusoidal phase-modulated spectra is calculated and analyzed. The simulations show that the intensity modulation at 3ω is much more serious compared to the other wavebands and it is mostly induced by the frequency conversion system rather than the amplification chain. The compensation effects of FM-to-AM conversion in the frequency conversion system by angular dispersion grating and cascaded crystals are numerically simulated and compared. Compared to the cascaded crystals, the angular dispersion grating could maintain higher frequency conversion efficiency with wide spectral width and offer a higher dynamic range of compensation effectiveness versus fundamental laser intensity. Combined with a precompensation filter before the amplification chain, FM-to-AM conversion at 3ω could be eliminated.