RECENT DRDO DEVELOPMENTS

Flash Lamp Pumped Er : Phosphate Glass Eye-Safe Laser

There is a potential problem  associated with most of the military  laser devices that these can easily cause retinal injury to the personnel who happen to come in the way of a laser beam even at a distance of several miles. Currently, rapid technological innovation is taking place in the field of eye-safe laser for most of the battlefield applications. Also for realistic training tactics, the use of an eye-safe laser has become highly desirable. Eye-safe lasers operating at ~1540 nm have the highest permissible ocular exposures accepted. From the point of view of the user, the laser shall be class- I and that can be used freely without the requirement to ensure that the target and other potential observers, including the operator of the laser system are suitably protected.

The Laser Science and Technology Centre (LASTEC), Delhi, has successfully developed a Flash Lamp Pumped Er:Yb:Cr: Phosphate Glass Laser generating a maximum output of 112 mJ @ 1540 nm at 35 J input in free running mode with 3 ms pulse and optimum output mirror reflectivity of 85 per cent. For this experiment, a highly close-coupled pump cavity was specially designed to pump the Er:Phosphate Glass Rod (Kigre-QE- 7S) of 3 mm dia and 50 mm length.
Performance curves at different output mirror reflectivitiesA high pressure ( 1000 torr) fused quartz enveloped, Xenon-filled flash lamp (Kigre K-1786) of 45 mm arc length and 3 mm inner bore dia with lamp impedance (Ko)=22.9 was employed. The pulse forming network was designed to produce current density of ~2200 A/ cm2. For critically damped condition, a capacitor of 500f, and inductor of 2.4 mH was employed with 375V capacitor charging voltage. A plano-concave resonator of 15 cm length was developed and free running performance was optimised. Figure 1 shows the performance curves for different output mirror reflectivities. Q-switching experiments are in progress. This centre is also in the process of developing similar Er:Phosphate glass laser material and their testing. Successful operation of the same would result in the development of an indigenous eye-safe laser .
 

Laser Window Glass for MiG-27 update

The development of Laser Window Glass (LWG) for MiG-27was undertaken indigenously on priority due to non-availability of the LWG from other sources for use with Laser Range Finder System (KLEN-PM) on MiG-27 aircraft. The Haryana State Electronics Development Corporation (HARTON), Ambala, has developed the LWG by using the fused silica glass with non-reflective coating. The Regional Centre for Military Airworthiness (RCMA) ,
Nasik, a field establishment of the Centre for Military Airworthiness & Certification (CEMILAC), Bangalore, with rich experience on MiG fighters has played a key-role in evolving the exhaustive test-schedule to meet the requirements which has become the basis for development of the LWG for the fighter aircraft. This test-schedule covers the random vibration test; high and low temperature; thermal shock solar raDIATion, blowing rain, salt-fog, sand and dust and combined temperature and altitude, and humidity tests.

The glass qualified all the tests with coefficient of transmission of more than 92 per cent. The LWG developed by HARTON was offered to a reputed firm for testing glass for both the wavelengths at their laboratory and found the coefficient of transmission 95 per cent and 93 per cent at λ=1.06m and λ= 1. 54m, respectively. This has brought along with metal frame considerable savings in FE.