Phase-front distortion of laser radiation in a turbulent atmosphere

Abstract

The phase-front distortion of laser radiation propagating through the turbulent atmosphere has been measured simultaneously at several wavelengths in the visible using a long-range Mach-Zehnder interferometer with high spatial and temporal resolution (476 nm </= lambda </= 647 nm, 0.5 mm </= Deltar 60 mm Deltat = 0.5 msec, z </= 2 km, C(n) = 1.3 x 10(-7) M(-1/3)). Phase-structure function, transverse coherence length, and arrival-angle fluctuations are interpreted in terms of the meteorological quantities turbulence strength and turbulence structure and inner and outer scale. The investigation covers the strong turbulence regime (scintillation saturation regime) where wave coherence is essentially determined by phase effects. In this regime a breakup of the phase front is found to occur.

Analysis of the fluctuations of a laser beam due to thermal turbulence

“…In reality we determine 0 to be 0.8 mm which is distinctly lower than that predicted by [21], of 1 ≤ ≤ 10 mm. This seems to be better fit with the results of [18], who refute the claim of [21]. It is further substantiation of the theoretical prediction that 0 does not have any strong dependence on wind velocity.…”

“…It can clearly be seen that D increases with an increase in L 0 . This verifies the relationship which was proved by [18], whereby they showed that even for a small outer scale ( L 0 = 0 4 m), the generation of turbulence energy was not confined to a scale less than L 0 , rather the energy is distributed over nearly all spatial scales. This relationship was first shown by [21], in a general case for all temperature fluctuations measured using fine wire probes.…”

“…[23], suggested that such data can be used to determine the normalized lens diameter for the limiting exposure. For small scales ( << 0 ), a prediction for the structure function is given by geometric optics [18,22], If r is below 0 , then the slope of Fig. 7 should be approaching a straight line with value of 2 [23].…”

Double pass wave structure function in weak to strong optical turbulence

“…However, experimental data presented by Gurvich and Kallistratova [3] contradict this conclusion. While many experimentalists have published wave structure function results that consider the wave structure function as a function of separation distance in the receiver plane ρ for a fixed value of turbulence strength [14][15][16][17][18][19][20], Gurvich and Kallistratova [3] presented one-way horizontal path wave structure function data as a function of increasing turbulence strength for a fixed value of ρ. The wave structure function developed from the standard Rytov method, commonly known as the five-thirds power law, does not agree with the data given in [3] in the moderate to strong turbulence regimes.…”

“…However, after completion of the integration, appropriate restrictions on the value of ρ can be made to eliminate the dependency of the wave structure function on the finite innerand outer-scale. The form of the small-scale filter function, equation (16), was chosen for mathematical convenience. The resulting wave structure function expressions were found to have the same qualitative behaviour as those obtained from the standard Rytov method when considered as a function of ρ.…”