Laser differential image-motion monitor for characterization of turbulence during free-space optical communication tests

Abstract

A laser differential image-motion monitor (DIMM) system was designed and constructed as part of a turbulence characterization suite during the DARPA free-space optical experimental network experiment (FOENEX) program. The developed link measurement system measures the atmospheric coherence length (r0), atmospheric scintillation, and power in the bucket for the 1550 nm band. DIMM measurements are made with two separate apertures coupled to a single InGaAs camera. The angle of arrival (AoA) for the wavefront at each aperture can be calculated based on focal spot movements imaged by the camera. By utilizing a single camera for the simultaneous measurement of the focal spots, the correlation of the variance in the AoA allows a straightforward computation of r0 as in traditional DIMM systems. Standard measurements of scintillation and power in the bucket are made with the same apertures by redirecting a percentage of the incoming signals to InGaAs detectors integrated with logarithmic amplifiers for high sensitivity and high dynamic range. By leveraging two, small apertures, the instrument forms a small size and weight configuration for mounting to actively tracking laser communication terminals for characterizing link performance.

FTIR characterization of atmospheric fluctuations along slant paths

“…Equation 1 demonstrates this relationship as a function of the following system parameters: (f) focal length, (λ) wavelength of laser, (d) distance between dual arm apertures, (D) diameter of apertures, and (σ 2 ) the statistical variation in the focal point locations. [1] ( )…”

“…We compare the turbulence measurements from the FTIR to those that are obtained simultaneously along the same atmospheric path with a custom Differential Image Motion Monitor (DIMM) [1] and commercial scintillometer [2]. Based on these side-by-side measurements we are able to develop a relationship between fluctuations in the atmospheric radiance collected with the FTIR and the measured background atmospheric turbulence values.…”

Turbulence Detection in the Atmospheric Boundary Layer Using Coherent Doppler Wind Lidar and Microwave Radiometer

“…Moreover, by adjusting the focal length and remaining at each height to reduce the variance of the distribution of lidar profiles, imaging methods that use the differential image motion monitor (DIMM) are effective methods for detecting turbulence intensity profiles [29][30][31][32][33][34][35]. Using atmospheric backscattering amplification phenomena by measuring the intensity of laser echo signal amplification effects can also calculate C 2 n under certain conditions [36][37][38].…”

Characterization of Pseudo-Random-Phase-Plate as a Kolmogorov/non-Kolmogorov turbulence simulator using statistical parameters and the phase structure function

“…Many researches have so far been reported in the literature on characterization of turbulence [10][11][12][13][14] and a description of its statistical properties [15][16][17][18][19][20][21]. Also, many research works highlight the techniques to simulate [22,23] and experimentally produce [3,4,[24][25][26] the same effects on a beam as are usually seen on propagation of a beam through atmospheric turbulence.…”