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Active optoelectronic system for stabilizing pulsed laser output energy at the fourth‐harmonic frequency

A feedback loop using an optoelectronic system has been tested successfully for the stabilization of the output energy at the fourth‐harmonic frequency of a Nd‐YAG laser (266 nm). The system presented includes an optical device to monitor the laser output energy at the nonconverted wavelengths and an electronic circuitry to optimize the laser output energy at the fourth‐harmonic frequency. This optimization is achieved by the real‐time correction of the frequency quadrupling laser crystal angle with respect to the input beam, using a stepping motor oscillating around the optimum crystal position. Results show that the present system provides a laser output energy stability better than ±15% for a long‐term operation at the fourth‐harmonic frequency, and keeps the locking even during the warming phase, immediately after the laser turning on. This system was designed for automatic LIDAR operations in field experiments, but its principle of operation can also be applied to any type of harmonic generator for e...