In complex laser systems, such as those used in inertial confinement fusion, achieving high-quality beam shaping is crucial yet challenging. This paper presents a multi-stage dynamic convergence strategy to mitigate near-field non-uniformity caused by multi-stage amplification and frequency conversion. Dynamic convergence functions dependent on fluence/power are derived through spatially modulated injection fields. An iterative control model from a spatial light modulator (SLM) to a third-harmonic (3ω) output is established for closed-loop regulation. Experimental results demonstrate that after 3 iterations, the modulation depth of the 3ω beam decreases from 1.8:1 to <1.5:1, with localized hotspot intensity significantly suppressed. This method, now routinely deployed in multiple large-scale laser facilities, enables high-precision near-field control while significantly reducing optical damage risks and ensuring high-fluence stability.

The spectral broadening scheme based on stimulated rotational Raman scattering (SRRS) with signal-beam injection has demonstrated kilojoule-level ultraviolet output with bandwidths exceeding 1%, showing potential for further suppression of laser-plasma instabilities. In this scheme, signal-beam injection into third-harmonic generation (THG) promotes additional sum-frequency mixing, thereby generating multiple spectral components. To further enhance spectral broadening, THG under dual-wavelength injection is investigated, enabling precise control of the input spectrum for SRRS. A coupled-wave dynamical model of THG under dual-wavelength injection is developed, revealing the synergistic effects of energy ratio and crystal detuning angle on the spectral distribution and conversion efficiency. Numerical simulations show that, by optimizing the dual-wavelength energy ratio and the detuning angle of the third-harmonic crystal, a balance between conversion efficiency and spectral broadening can be achieved. This work provides a theoretical framework for harmonic generation under dual-wavelength injection, with potential to further improve SRRS spectral broadening and inspire advances in multi-line frequency generation.

Phase-modulated (PM) spectral failsafe systems are necessary to promptly terminate amplification processes following accidental seeding of a high-power laser chain with a non-PM pulse to prevent optical damage. In this work, we present a reliable spectral failsafe system that can indicate the presence or absence of sufficient PM light. This requirement is met by combining dual temperature-sensitive fiber Bragg gratings detection with high-speed RF amplitude comparisons. The failsafe trigger signal is generated when the spectral power at the peak sideband exceeds that at the center. The spectral failsafe system has the ability to distinguish between adequate and inadequate PM pulses, and it exhibits significant robustness in pulse width, TEC temperature drift, and DFB wavelength drift in experiments, making it valuable for safe high-power laser operations and providing a useful reference for other detection system designs.

In order to measure the third harmonic conversion efficiency curve of the KDP crystal, it is usually necessary to carry out several or even dozens of experimental shots at different power density points to obtain data. The experiment data researchers obtained is limited and the cost is high. In this paper, a fast method to measure the third harmonic conversion efficiency of the KDP crystal at different power density points is proposed. By artificially constructing the spatial near-field modulation with continuously varied energy, it is feasible to obtain different power densities at different spatial points in the beam aperture with one shot. The experimental results show that this method can quickly measure the third harmonic conversion efficiency curves of the KDP crystal at different power densities with fewer shots.