Measurement of atmospheric turbulence parameters relevant to adaptive optic system design

Anil K. Razdan

doi:10.1117/12.479215

30 April 2003 Measurement of atmospheric turbulence parameters relevant to adaptive optic system design

Anil K. Razdan

Author Affiliations +

Proceedings Volume 4976, Atmospheric Propagation; (2003) https://doi.org/10.1117/12.479215
Event: High-Power Lasers and Applications, 2003, San Jose, CA, United States

Abstract

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 (C_n²) 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.

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Anil K. Razdan "Measurement of atmospheric turbulence parameters relevant to adaptive optic system design", Proc. SPIE 4976, Atmospheric Propagation, (30 April 2003); https://doi.org/10.1117/12.479215

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