FM-to-AM conversion comparison of typical second-order phase modulation signals

A high-quality temporal pulse shape is essential to ensure the stability of inertial confinement fusion experiments such as NIF, LMJ, and SG-III. Spectral broadening is necessary to avoid stimulated Brillouin scattering and to smooth the focal spot on target. However, spectral modulation might result in frequency modulation to amplitude modulation (FM-to-AM) conversion with later optical elements impact such as grating and crystals. Four different periodical second-order phase modulation signals-sinusoidal, Gaussian, Singher and quadratic signals are designed with the newly Arbitrary Wave Generator (AWG). And the FM-to-AM conversion are compared after the effect of transfer function by gratings or crystals. Results show that the designed periodic Gaussian signal has the smallest FM-to-AM conversion of 2.93%. Compared to the commonly used sinusoidal signal, Gaussian signal has realized a reduction of more than 200%. FM-to-AM conversion can be reduced by a careful design of the modulation signal.