Spatial characteristics of a Nd : YAG laser for pulsed rangefinder over broad ambient temperature range
Abstract
Spatial characteristics of a pulsed laser based on neodymium-doped yttrium aluminium garnet (Nd : YAG) rod with conductively cooled barrel surface are investigated for use as part of airborne rangefinding systems for a pulse energy values not less than 80 mJ at a wavelength of 1064 nm. Diode side-pumping system configuration has been developed for a Nd : YAG rod with a diameter of 4 mm and Nd3+ ions concentration of 0.9 at. % with pump efficiency not less than 0.65. The pump light absorption profiles have been calculated for various central pump light wavelengths, and the value of thermal lens in laser rod has been determined for pulse repetition rates of 1.0; 4.0; 12.5; 22.0 Hz using the OpticStudio and LASCAD softwares. Laser beam divergence has been evaluated for a flat-flat resonator with variable internal lens. Spatial distribution of laser beam was experimentally studied in the far field over ambient temperatures range of –40 to +60 °С for pulse repetition rates of 1.0; 4.0; 12.5; 22.0 Hz while stabilising diode pumping source temperature by Peltier module. It is shown that divergence for a beam containing 86.5 % of total energy does not exceed 1.9 mrad. Double standard deviation of the far-field laser beam profile centroids relative to averaged centroid position for a pulse repetition rate of 4.0 Hz does not exceed 0.5 mrad at a fixed temperature for pulse repetition rates of 1.0; 4.0; 12.5; 22.0 Hz and recorded pulse number not less than 45. The obtained values of divergence and double standard deviation of the far-field laser beam profile centroids show the possibility to use the laser as part of rangefinder on board unmanned aerial vehicles.
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