Brightness enhancement of a compact, high energy, passively Q-switched Nd:YAG laser using volume Bragg gratings (Conference Presentation)

Abstract

For many Q-switched lasers, it is desired to maximize the pulse energy while minimize the pulse duration. Such high energy, short pulse output can be achieved by pumping with large mode diameters and maintaining a cavity length of a few centimeters. However, increasing the mode area of the resonator while keeping the same cavity length causes the excitation of higher order transverse modes and consequently decreases the brightness of the output radiation. To overcome this drawback, angular mode selection technique with transmitting Bragg grating (TBGs) was implemented inside the cavity in order to suppress the higher order transverse modes, allowing for near diffraction limited and high brightness output. Since a Bragg gratings angular selection works only in one transverse direction, two orthogonal gratings were implemented for mode selection in both transverse directions. A compact high energy passively Q-switched Nd:YAG laser is presented showing output pulses with 1 mJ of energy and 1.5 ns of duration. Due to the compact design requirements and to obtain such high energy, the resulting laser had large mode diameter and was multimode. The laser consists of a 5 mm thick slab of Nd:YAG, a 3 mm thick slab of Cr:YAG with a 65% transmission, and a 40% output coupler. Two TBGs were implemented in the cavity, orthogonal to one another, for mode selection in both transverse directions. Experimental results are presented demonstrating a 5x improvement in the beam quality of the system after implementing the TBG mode selection approach.