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RECENT DRDO DEVELOPMENTS

Transverse Excited Atmospheric Carbon dioxide Laser

The Institute of Armament Technology (IAT) , Pune, has successfully Transverse excited atmospheric carbon dioxide laserdesigned and developed a high-power    transverse excited atmospheric (TEA) carbon dioxide laser using  double discharge uv pre-ionisation. It involves the use of trigger discharges to generate a uniform ionisation layer near the cathode before the onset of the main discharge. The electrons produced by the UV photo-emission at the cathode are released into the laser volume, resulting in a fast change of discharge impedance.  By this, the required pre-ionisation density for a
stable glow discharge (which is ne = 106-108/cm3) is met with.

The laser head consists of a chang profiled aluminium cathode (to ensure a uniform field over the surface of the electrode) and a flat aluminium anode defining an active volume of 120 cm3 . The optical resonator is a perspex cavity of 30 cm diameter and 60 cm length. It uses a nearly 100 per cent reflecting gold coated copper mirror of 4 m radius of curvature and 80 per cent reflecting ZnSe output coupler separated by a distance of 80 cm. The laser is excited by discharging electrical energy from the storage capacitor of 25 nf via a charge transfer circuit triggered by a thyratron switch in discharging phase. The pre-ionization involves sparks created between inductively coupled spark pins and the sharp edges of the electrodes, which ensures high current density required for high degree of pre-ionisation. Consistent discharge glow is available for input voltages of 15-17 kV for the gas mixture of 1: 1 : 8 ratio of CO2 :N2: :H: at cavity pressure of 100-350 Torr.  For uniform UV emission at each pin for the specified gas mixture, a 33 ÁH inductance was found to be optimised. Pulses of 42 mJ energy could be obtained. Pulse repetition rate up to 5 Hz with peak power in the range of few MW has been measured from the system.

Action is in progress to incorporate gas recycling system and to increase the pulse repetition frequency. Experiments are being carried out for improvement and optimisation of the laser performance for varying gas mixture ratio. With the present efforts. the system would be useful for tactical range finding, photochemistry and laser isotope separation for separating C-13 isotope using Freon -22 ( CHCLF2).

Gas Chromatography-Mass Spectrophotometry [GC-MS] Facility

The Defence Bio-Engineering & Electro-Medical Laboratory (DEBEL), Bangalore, Dr Aatre being briefed about working of gas chromatography-mass spectrophotometry facilityhas recently installed a gas chromatography-mass spectrophotometry [GC-MS] facility for the analysis of complex mixtures of chemicals and other matrices. It is one of the most sensitive equipment for the structural identification of compounds and concurrent determination of their molecular weights.

The applications of GC- MS in the areas of physical, chemical  and life sciences are innumerable. Being a valuable analytical tool it is widely used in several industries, including petrochemical, pharmaceutical, paint, polymer, agricultural and food industries.  Besides, this facility is also used for routine biochemical analysis, pollution analysis, forensic studies and ambient air analysis.