Effects of underwater turbulence on laser beam propagation and coupling into single-mode optical fiber.

We characterize and compare the effects of turbulence on underwater laser propagation with theory. Measurements of the coupling efficiency of the focused beam into a single-mode fiber are reported. A simple tip-tilt control system, based on the position of the image centroid in the focal plane, was shown to maintain good coupling efficiency for a beam radius equal to the transverse coherence length, r(0). These results are relevant to high bandwidth communication technology that requires good spatial mode quality.

Laser propagation at 1.56 microm and 3.60 microm in maritime environments.

We report results from field experiments that have compared laser propagation at 1.565 microm and 3.603 microm in a variety of atmospheric conditions in a low-altitude maritime environment in order to quantify the relative effects of turbulence under realistic conditions. Intensity scintillation and normalized focused spot sizes were found to be significantly less affected by turbulence at the longer wavelength, in general agreement with theoretical predictions. Also, the longer wavelength beam was noticeably less degraded by aberrations in the transceiver optical components. These advantages should be considered when evaluating the wavelength trade-offs in laser communication systems.

Fluorescent volumetric display excited by a single infrared beam.

A volumetric display technique that uses fluorescence excited by a single infrared beam is proposed. A convergent laser beam is used to activate ions locally around the focal point. Three-dimensional scanning by the focal point is achieved by moving an inclined image plane in the direction perpendicular to an optical axis. Preliminary experimental results of three-dimensional image generation in an Er(3+)-doped fluoride glass excited by a laser beam of 810 nm wavelength are presented.

Coherent laser radar at 3.6 microm.

Coherent laser radar systems in the mid-IR wavelength region can have advantages in low-altitude environment because they are less sensitive to scattering, turbulence, and humidity, which can affect shorter- or longer-wavelength system. We describe a coherent laser radar at 3.6 microm based on a single-frequency optical parametric oscillator and demonstrate the system over short ranges outdoors. The system was used to make micro-Doppler measurements from idling trucks that were processed to give surface vibration spectra.