Investigation of stimulated rotational Raman scattering of the high-power broadband laser with applied angular dispersion

Smoothing by spectral dispersion （SSD） leads to considerable improvement on laser-irradiation uniformity in far field for fusion lasers. Phase modulation in time and spectral angular dispersion （SAD） across the beam introduced by SSD will affect the stimulated rotational Raman scattering （SRRS） gain in the near field. This paper focuses on the influence of SAD on SRRS gain under different laser conditions. Results show that the SAD will aggravate the generation of SRRS when the laser initial additional phase is constant. On the contrary, the SAD can reduce the SRRS gain if appropriate SSD parameters are adopted when the laser initial additional phase is variable. SSD has a certain application prospect in SRRS suppression.

Linear angular dispersion compensation of cleaned self-diffraction light with a single prism

The linear angular dispersion of a self-diffraction(SD) pulse, from a femtosecond laser pulse cleaning device, is compensated for by the use of a single prism. More than 500 μJ first-order SD pulse has a contrast of 1012, which is about five orders of magnitude improvement from the input fundamental pulse. The wings of the distribution away from the main pulse in ±1 ps are cleaned with a contrast improvement of about 107, which verifies the pulse cleaning ability of the SD process.

Describing spatiotemporal couplings in ultrashort pulses using coupling coefficients

Three coupling coefficients are defined to describe spatiotemporal coupling in ultrashort pulses. With these coupling coefficients, the first-order spatiotemporal couplings of Gaussian pulse and beam are described analytically. Also, the first-order and the second-order spatiotemporal couplings caused by angular dispersion elements are studied using these coupling coefficients. It can be shown that these coupling coefficients are dimensionless and normalized, and readily indicate the severity of spatiotemporal coupling.

Enhanced wide-angle third-harmonic generation in flat-band-engineered quasi-BIC metagratings

Nonlinear metasurfaces and photonic crystals provide a significant way to generate and manipulate nonlinear signals owing to the resonance-and symmetry-based light-matter interactions supported by the artificial structures.However,the nonlinear conversion efficiency is generally limited by the angular dispersion of optical resonances especially in nonparaxial photonics.Here,we propose a metagrating realizing a quasi-bound-state in the continuum in a flat band to dramatically improve the third harmonic generation(THG)efficiency.A superior operating angular range is achieved based on the interlayer and intralayer couplings,which are introduced by breaking the mirror symmetry of the metagrating.We demonstrate the relation of angular dispersion between the nonlinear and linear responses at different incident angles.We also elucidate the mechanism of these offaxis flat-band-based nonlinear conversions through different mode decomposition.Our scheme provides a robust and analytical way for nonparaxial nonlinear generation and paves the way for further applications such as wide-angle nonlinear information transmission and enhanced nonlinear generation under tight focusing.

Transmissive angle-multiplexed meta-polarizer based on a multilayer metasurface

Metasurfaces have exhibited great capabilities to control electromagnetic waves,and many multifunctional metasurfaces were recently proposed.However,although angle-multiplexed meta-devices were successfully realized in reflection geometries,their transmission-mode counterparts are difficult to achieve due to the additional requirements.Here,we design and fabricate a transmissive angle-multiplexed meta-polarizer in the microwave regime based on a multilayer metasurface.Coupled-mode-theory analyses reveal that the device exhibits distinct angle-dependent transmissive responses under excitations with different polarizations,and such differences are further enhanced by multiple scatterings inside the device.Microwave experimental results are in good agreement with numerical simulations and theoretical analyses.