Measurement of gain-saturation properties of a Q-switched Nd:YAG laser oscillator with a three-pass amplifier and corresponding beam diagnosis

Abstract

Here, a homemade Q-switched Nd: YAG laser oscillator alongside a three-pass amplifier has been designed and fabricated. The oscillator operates nearly in the fundamental mode and the spot size/phase front curvature is determined by making use of ABCD law regarding the thermal lensing effect. To scale-up the pulse energy in a compact volume, a three-pass amplifier arrangement is coupled to the oscillator. The systematical measurements to obtain the small-signal gain and saturation properties are carried out in terms of various pumping energies. Simultaneously, the output beam from the oscillator and triple-pass amplifier are well diagnosed to determine output energy, pulse duration, spectral width, M2 factor and the radius of curvature. Despite the oscillator pulse giving out 60 mJ, 13 ns however, the output pulse of 800 mJ, 1 Hz, 9 ns at 1064 nm with FWHM 0.024 nm and beam quality factor M2= 2.21 are determined in favor of multi-pass amplifier. Scaling up the pulse energy up to 800 mJ it is shown that the output beam alters its phase front from the initial planar wave to the spherical curvature during the propagation through a multi-pass amplifier due to the elevation of a radial temperature gradient. Eventually, the novelty of this manuscript arises from the effect of energy scale-up on the gain and saturation in laser amplifier and their correlation with the output beam properties.