Doppler-induced continuous spectral broadening and beam smoothing of ultraviolet lasers

Abstract We propose a compact scheme based on ultrafast-rotating phase plates (URPPs) to realize continuous spectral broadening of ultraviolet lasers. The rapid rotation elements behave as a random oscillator which induces Doppler frequency shift into the ultraviolet lasers. Theoretical relations between the keys parameters and spectral broadening are verified by numerical simulations. The results reveal that the spectral bandwidth has a linear correlation with the modulation frequency fm.Greater spectral broadening can be achieved by raising the rotation speed, enlarging the effective radius, or reducing the size of phase elements. When multiple URPPs are connected in series, the superimposed spatiotemporal modulation further boosts continuous spectral broadening and delivers superior speckle smoothing performance.This scheme can be adopted not only to broaden the discrete spectra of optical frequency combs and suppress stimulated Brillouin scattering in high-power fiber lasers,but also possesses great potential for mitigating laser-plasma instabilities in inertial confinement fusion.