Experimental measurements to investigate the effects of atmospheric turbulence on two major parameters for laser adaptive optic (AO) system design (turbulence coherence length r0 and the atmospheric time constant τ0) were carried out to cover weak, moderate and strong turbulence conditions prevailing in the city of Delhi (India). Diurnal and seasonal variation of atmospheric refractive index structure parameter (Cn2) near the ground was measured with a minimum and maximum recorded values of 2 × 10-13 m-2/3 and 1011 m-2/3 respectively. Estimated values of r0 range from 0.42 mm to 4.4 mm (for 0.6328 μm wavelength of He-Ne laser), 0.8 mm to 8.3 mm (for 1.06 μm wavelength of Nd:YAG laser), 1 mm to 10.5 mm (for 1.3 μm wavelength of Chemical Oxy-Iodine laser), 3.7 mm to 38.2 mm (for 3.8 μm wavelength of DF laser) and 12.5 mm to 131 mm for 10.6 μm CO2 laser wavelength, each for measured Cn2 values of 1011 m-2/3 to 2×10-13 m-2/3. Intensity autocorrelation function measurements of laser scintillations indicate that a bandwidth of ~ 0.5 kHz (corresponding to measured τ0 ~ 2.25 ms) is required for the adaptive optic system to operate effectively in our conditions. Laser beam wander exceeding 100 μrad (both at 0.6328 μm and 1.06 μm wavelengths) at frequencies ranging from 10-20 Hz were observed under strong turbulence conditions. Estimation of number of correction zones for deformable mirror indicate that for the measured turbulence strengths in our atmosphere, the complexity of the AO system at 1.06 μm, 1.3 μm and 3.8 μm wavelengths will be very high as compared to 10.6 μm system where the actuator requirements are much less and within manageable range.
Various essential parameters like mass transfer coeff, volumetric flow rates etc. for a typical KW level COIL have been considered and the gas residence time and thus the size of the SOG has been estimated. The SOG based on this design has been fabricated and is under evaluation. The design of SOG and various other subsystems like nozzles, resonator and liquid nitrogen trap have been discussed in this paper. Further systematic studies have been carried out on the shelf life of basic hydrogen peroxide (BHP) in the temperature range of -10°C to +10°C using titration technique. Studies indicate that the solution prepared at -10°C to -15°C and stored at this temperature, the decomposition starts only after 36-42 hours. However, at higher storage temperatures, the decomposition is faster.
We report measurements of the statistical properties associated with the intensity fluctuations of a He-Ne laser propagated through a laboratory simulated atmospheric turbulence as well as through the open air atmospheric turbulence region. From these measurements the probability density function representative of the random process was identified by comparing the measured parameters with those of standard theoretical models. Photon counting techniques have been used in all our measurements.
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