RECENT DRDO DEVELOPMENTS

All Solid-State Nd:YAG Laser

The Institute of Armament Technology (IAT), Pune, has successfully designed and Experimental setup of diode-pumped Q-switched Nd:YAG laser.fabricated an efficient operation of diode-pumped Nd:YAG laser. Recently, high power laser diode arrays/bars have been found to be promising alternative to the conventional lamps used for pumping solid-state crystals. In  solid-state lasers, laser crystals are optically pumped by conventional flash lamps or arc/filament lamps. A number of special features exhibited by these pump laser diodes are: good spectral match between laser diode emission and peak of the crystal absorption band, narrow spectral line width, little excess heat generation, spectral brightness amplification, longer operational lifetime, small size, and lightweight. Thus, the new class of solid-state lasers, popularly known as diode-pumped solid-state lasers has been highly efficient, compact, rugged and reliable. Such an all solid-state laser device can find potential applications not only in military but also in scientific, industrial, commercial, medical and biomedical areas.

The Nd:YAG crystal of 2 mm dia and 20 mm length was transversely pumped by a GaAlAs laser diode array emitting at 0.808 Ám. The crystal was directly side-coupled with the laser diode in a gold-plated cylindrical pump cavity. Using an optimally designed resonator configuration, a maximum of 4.6 mJ pulse energy was obtained, which corresponds to optical-to-optical total efficiency of 25 per cent and a slope efficiency of 37 per cent. The laser Experimental setup of diode-diode was operated for pulse width of 200 Ás at a repetition rate of 13 Hz. The far-field transverse mode structure was found to operate efficiently on low-order spatial modes. The Nd:YAG laser was also acousto-optically Q-switched to produce nearly 1 mJ, 100 ns pulse, operating even up to 100 Hz without adequate cooling requirement. The system is 12 per cent electrical-to-optical efficient. Presently, the output pulse energy is limited, which can be scaled up by incorporating more laser diode arrays in series. To achieve high average power from diode-pumped solid-state lasers, a liquid cooled heat sink is indigenously designed and fabricated. Work is in progress for designing a prototype of compact and miniaturized diode-pumped Q-switched Nd:YAG laser system.

Further effort is on to experiment other Nd-doped laser crystal which can be similarly pumped by the laser diode array. Other non-linear techniques, viz., harmonic generations and parametric oscillation and amplification would be attempted in future for studying other laser raDIATions from diode-pumped solid-state lasers.

Electromechanical Actuation System Servo Controller

Electromechanical actuation system servo controllerThe Naval Science & Technological Laboratory (NSTL) , Visakhapatnam, in association with Srijan Controls Drives, Pune; CEERI, Pilani; and Bharat Electronics Ltd, Bangalore, has developed an electromechanical actuation system servo controller for application in light weight torpedo. The actuation system is configured around a brushless DC (BLDC) motor and the electronic hybrid servo controller. The BLDC motor contains rare-earth magnets and Hall Effect sensors for position sensing. The hybrid controller has built-in error amplifier, compensator, electronic communication logic, PWM amplifier, and high power MOSFET/BJTH bridge. The BLOC servo controller development involves: (i) functional design and development of the controller to meet all the requirements of motor bandwidth and power, and (ii) miniaturization of the controller adopting advanced hybridization techniques of die bonding, wire bonding, metal encapsulation techniques, and efficient thermal management to meet the weight and size specifications.