Vaughan Jm

Coherent laser radar in Europe

European work in coherent laser radar with 10 /spl mu/m and shorter wavelength lasers is reviewed. Fundamental aspects include heterodyne studies of signal statistics and fluctuations, and detailed experimental and theoretical work on signal amplification and autodyne arrangements with light reinjected into the laser cavity. Progress with lasers, detectors, and modulators has led to the development of several compact robust field systems both continuous-wave and pulsed. Various ground-based programs are described including local wind field measurement and wake vortex investigation at airfields, and study of range, image, and Doppler shift of hard targets. Airborne systems have investigated avionics problems of true airspeed, pressure error, and wind shear warning. Other airborne studies include ground imaging, obstacle warning, terrain following, and a compendium of atmospheric backscattering over the North and South Atlantic. In recent years, the European Space Energy has supported studies and technology development for a space-borne wind lidar in the Atmospheric Laser Doppler Instrument (ALADIN) program.

The fractal character of Gaussian-Lorentzian light

Abstract A heterodyne technique has been used to study the Lorentzian-broadened light (with Gaussian statistics) produced by laser illumination of particles in Brownian motion. It is demonstrated that intensity time-sequences for this type of light exhibit a fractal character, possessing fluctuations over nearly a three-decade range of timescale. This is in contrast with the much smoother fluctuations observed for Gaussian-broadened light. The potential of heterodyne methods for application to other demanding problems is briefly outlined.

Noise and gain in sub-threshold laser modes

Abstract When have observed intensity-fluctuation noise centred around the frequency corresponding to the longitudinal mode separation for a single-mode argon-ion laser. The noise arises from beating between the lasing mode and spontaneous emission into the subthreshold modes on either side. The noise profiles are compared with gain profiles obtained for above-threshold laser amplification of an injected signal. Both sets of profiles broaden and shift with increasing laser power and appear identical in the case of symmetric sub-threshold modes. However, remarkable differences between noise and gain are observed for asymmetric tuning. The results are in good agreement with a theory for the gain which incorporates field coupling at signal and image frequencies via modulation of the population inversion.

Inter-transverse-mode injection locking and subthreshold gain measurements in a CO/sub 2/ waveguide laser

A higher order CO/sub 2/ waveguide laser resonator mode has been studied both above and below threshold, by reinjecting a frequency shifted portion of the laser output back into the resonator. The relative reinjected (autodyne) gain profile in the vicinity of the subthreshold transverse mode is shown to shift in frequency, reduce in spectral width, and increase in magnitude as the subthreshold mode is brought nearer to threshold by tilting one of the resonator mirrors. Once above threshold, inter-transverse-mode injection locking has been demonstrated, and close to the locking-point higher order terms from the nonlinear interaction are clearly evident. >