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We report the use of a windowless resonant spectrophone to make highly sensitive (10-9 cm-1) photoacoustic measurements of atmospheric water vapor and aerosol absorption. A tunable high-resolution cw Nd:YAG laser was used to measure the water vapor lines and aerosol absorption spectrum at 1.064 mm. The water vapor absorption lines were used to calibrate the spectrophone for the aerosol measurements. The spectrophone was also calibrated using the theoretical expression with an independent measurement of the Q of the spectrophone. The initial windowless spectrophone has the ability to make in situ real- time measurements of atmospheric absorption to an accuracy sufficient for thermal blooming calculations. The ability of the spectrophone to detect at the 40-parts-per-trillion-level of other gaseous and volatile species is discussed. The use of resonant mufflers to isolate the spectrophone from external noise is also presented.© (1994) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.

We report the application of an actively stabilized CW mode-locked Nd:YLF laser to the problem of range-Doppler imaging. A laboratory demonstration of cm range and cross-range resolution is described. The effect of target speckle and glint on signal-to-noise ratio (SNR) and signal processing are discussed. Because of the wide range of mode-locked pulse and pulse train durations achievable with the solid state laser system, the single shot signal-to-noise ratio can be maximized. A Nd:YLF oscillator and Nd:glass amplifier laser system has distinct advantages over other high power laser systems in range-Doppler applications.

The authors have stabilized the frequency of a cw, lamp-pumped, mode-locked Nd:YLF oscillator. The output pulse duration is 50 ps and, simultaneously, the mode jitter is less than 25 kHz relative to a stable, high-finesse Fabry-Perot. The frequency shifts and broadening of the oscillator modes caused by pulsed amplification in a flashlamp-pumped Nd:glass rod with a gain of 100 have been measured. Broadening and frequency shifts on the order of 10 kHz are induced by the amplifier. The changing population of the active transition in the amplifier is the dominant source of the frequency shifts. For frequency-stable amplification, significant saturation of the gain medium must be avoided.

The Gound-Based FEL Technology Integration Experiment's high power laser requires a beam director-dome window to protect the optics from dust accretion and reduce the optical aberrations occurring in the air interface between the dome interior and exterior. One half of the dual aerocurtain designed for this purpose is heated 18 C above ambient temperature, while the other is not heated; this results in the development of two mixing zones, (1) between the heated and unheated halves, and (2) between the latter and the room air. This aerocurtain configuration is shown to reduce the Strehl ratio loss through the window to several percent.