We experimentally study energy scaling properties of gas-filled multipass cell-based nonlinear compression setups by employing increasing azimuthal orders of Laguerre-Gauss LG0ℓ modes. First, we analyze the mode conversion from a Gaussian beam to LG0ℓ modes using spiral phase plates and spatial low-pass filtering. Then, these beams are sent to a first gas-filled multi-pass cell (MPC) to verify the energy scaling and spatial properties at the output. In a second experiment that allows more nonlinearity, we compare pulse compression conducted with either a Gaussian or an LG03 beam in terms of energy scaling, output temporal, spatial, spatio-spectral, and spectrally-resolved topological charge properties. The use of this structured beam allows for an increase in the input energy from 50 μJ up to 150 μJ with a final pulse duration of 60 fs, while the other parameters are essentially kept equal.

Laser optoelectronic transceiver systems are widely used in space, aviation, and ground platforms. Accurate control of focal positions in the terminal optical path is critical for energy concentration and imaging quality. Conventional laboratory focusing methods use large-aperture, long-focal-length collimators or star-point targets. These systems are bulky and difficult to deploy with the terminal. After environmental tests, they hardly support refocusing calibration or quantitative evaluation of transmitter defocus and divergence. To address these issues, a Gaussian-beam-based alignment and calibration method is proposed. The method enables camera focusing and the measurement of the object-side defocus and beam divergence angle of the transmitting fiber collimator, while a corresponding theoretical model is established. It employs a fiber collimator with fixed divergence. Gaussian spot profiles are fitted within a limited space, which allows high-accuracy quantification of focal length and object-side defocus. Simulation and experimental results consistently confirm the effectiveness of the proposed approach. Compared with the collimator-based focusing method, the mean focal length is closer to the nominal value. The maximum relative error of the focal length is reduced by about 81.3%, and the root-mean-square deviation is reduced by about 80.7%. The deviations of object-side defocus and divergence from theory are within 2%. The method has a compact structure and modest calibration requirements. It is suitable for terminal alignment, recalibration, and focus inspection under static or quasi-static conditions, and provides an effective technical approach for high-precision, miniaturized, and scalable engineering implementation of focusing.

Energy stability in multi-pass chirped-pulse amplification (CPA) amplifiers is critical for precision applications such as laser wakefield acceleration. This study employs theoretical and numerical methods to analyze the impact of seed and pump-source energy jitter on output stability. Perturbation analysis and Monte-Carlo simulations confirm that in the saturation regime, pump-source jitter dominates the output instability of a multi-pass amplifier. A dual stabilization strategy is therefore proposed and experimentally validated: the total pump fluctuation is reduced by a factor of 1/n through the statistical averaging of multiple independent pump sources, while the saturation operation further suppresses residual jitter propagation. Experiments on a 200 TW Ti:sapphire system demonstrate the effectiveness of both approaches. Under similar saturation levels, a four-pump configuration yields lower output jitter than a two-pump setup, and stronger saturation significantly improves stability for the same number of pumps. This work provides a clear and predictive framework for designing high-stability CPA drivers for advanced applications.