DEVELOPMENT OF COMPACT PASSIVELY Q-SWITCHED DIODE PUMPED ND:YAG LASER SYSTEM
The Laser Science and Technology Centre (LASTEC), Delhi, has successfully developed a highly compact passively Q-switched Diode Pumped Nd:YAG Laser System. It generates 5mJ @10 pps in 20 ns which will lead to the development of ultra compact, high repetition rate laser systems for various military applications like target designation and range finding. The system combines advantages of both, diode pumping and passive Q-switching, techniques which results in compact and robust system with much simpler design than their conventional counterparts.
The system is modular in design with separate Laser Head and Laser Diode Driver modules of 4.2 x 8.2 x 16.4 cm and 7 x 8.3 x 26 cm size, respectively, which have been specially designed for compactness and easy maintenance. In the laser head, the resonator components are independent from the pump source due to special mounting configuration. The plano-concave resonator consists of an Nd:YAG laser rod of 5 mm dia and 50 mm length, and a Cr4+:YAG passive Q-switch crystal of 10 mm dia with optimized initial transmission of 70 percent. Cr4+:YAG has the advantage of high damage threshold and good thermal conductivity as compared to other passive Q-switches like dyes and colour center crystals.
Four fast axis collimated Quasi-CW laser diode linear bar arrays with 100W peak power and peak emission wavelength of 808 nm, efficiently side pump the laser rod. Arrays, connected in series, are driven by indigenously developed laser diode driver which generates 200 micro sec square pulses @ 10pps with 120A peak current. Driver is one of the critical components of the overall Diode Pumped Solid State Laser (DPSSL) system due to the design complexities involved in delivering high peak current pulses with desired rise time, overshoot and droop characteristics. Its soft start feature protects the vulnerable diode arrays from power on transients and ensures safe and reliable operation of the system. It operates from a 12V battery power pack, which is an integral part of the driver package and occupies about one third of the package volume. The system can be operated in both, single shot and repetitive mode of 10 pulses per sec.