Study on beam quality of DF laser with inner cavity unstable resonator

Laser beam quality is one of the key indicators to measure the application performance of laser. To meet the application requirements of long-distance optoelectronic countermeasures, we cany out the research on the design of unstable resonators and beam quality improvement techniques for non-chain pulsed deuterium fluoride (DF) lasers. Three sets of positive branch virtual confocal unstable resonators with different magnifications are designed. An inner cavity unstable resonator with two support structures of convex mirror, transverse support and longitudinal support, are constructed. The transverse support structure is equipped with a circulating water-cooling channel. Using 86.5% surrounding energy to define laser beam diameter, the laser beam quality is evaluated with beam quality factor beta , and the energy and beam divergence for two support types of convex mirrors are compared. It can be found that, under the same conditions, the laser energy of unstable resonators with longitudinal support is 6% higher than that of the transverse support structure, but the far-field divergence angle is 9% larger than that of the transverse support structure. Although the watercooled transverse support structure has energy shielding, its good thermal stability significantly improves the quality of the laser beam. Laser beam with a beam quality factor beta of 1.83 and a divergence angle theta 0.865 of 0.63 mrad is obtained under the transverse support unstable resonator of M =2.25. Under this condition, the laser single pulse energy is 2.34 J, the laser pulse width is 88.2 ns, and the peak power reaches 26.5 MW.