Spectral broadening via phase modulation is widely employed in high-power laser systems to suppress transverse-stimulated Brillouin scattering and improve beam uniformity.However, non-uniform spectral transmittance and group velocity dispersion can induce frequency modulation-to-amplitude modulation (FM-to-AM), threatening the safety of large-aperture optics.Current monitoring techniques rely on high-speed oscilloscopes and wavelength conversion, thereby increasing the cost and complexity.This study presents a real-time FM-to-AM detection method based on a dual-comparator delayunlocked detection architecture.The system employs a high-speed photodetector, lownoise amplifier, envelope detection, and delay-unlocked dual-comparator.The module reliably measures modulation depths from 1.27% to 19.15% for pulses with a rise time of < 60 ps and a modulation frequency of 20 GHz.This compact, low-cost, and modular design enables robust FM-to-AM monitoring without high-speed oscilloscopes, facilitating realtime feedback and enhancing the operational stability in large-scale laser drivers, while offering scalability for multi-channel deployment in future inertial confinement fusion facilities.
Teng et al. (Mon,) studied this question.