Coherent laser radar performance for general atmospheric refractive turbulence

Area of Science:

• Optical engineering
• Atmospheric physics
• Signal processing

Background:

• Coherent laser radar (or lidar) systems rely on heterodyne detection for high sensitivity.
• Understanding signal-to-noise ratio (SNR) and heterodyne efficiency is crucial for system performance.
• Atmospheric turbulence is a known factor that can degrade optical system performance.

Purpose of the Study:

• To investigate the signal-to-noise ratio (SNR) and heterodyne efficiency in coherent laser radar systems.
• To incorporate the effects of atmospheric refractive turbulence into the analysis.
• To provide a general framework applicable to various configurations and conditions.

Main Methods:

• Utilized the Fresnel approximation and a general formulation for laser radar analysis.
• Employed the path-integral formulation to include atmospheric refractive turbulence effects.
• Analyzed system components (transmitter, receiver, local oscillator) using untruncated Gaussians.

Main Results:

• Developed a general expression for SNR in terms of direct detection power and heterodyne efficiency.
• Demonstrated that the assumption of statistically independent paths is valid for weak turbulence under the Markov approximation.
• Showed that SNR can double in the limit of large path-integrated refractive turbulence compared to the statistically independent-path result.

Conclusions:

• The study provides a comprehensive analysis of SNR and heterodyne efficiency in coherent laser radar, including atmospheric turbulence.
• Identified physical mechanisms reducing heterodyne efficiency by performing calculations in the receiver plane.
• The findings offer insights into optimizing laser radar performance in turbulent atmospheric conditions.