John C. Walling

Spectroscopic properties of alexandrite crystals II

Abstract Several aspects of the optical spectroscopic properties of alexandrite crystals not previously investigated are reported here. For Cr3+ ions occupying the Al3+ lattice sites with mirror symmetry in BeAl2O4, the positions of the zero-phonon lines for absorption transitions to the 2T1g and 4T2g levels are identified, and vibronic transition peaks in the fluorescence spectrum are compared to transitions appearing in the Raman spectrum and Stokes excitation spectrum. In addition, the effects of radiation trapping are shown to lengthen the fluorescence lifetime of the 2Eg - 4A2g transition for ions in these sites at low temperatures. For Cr3+ ions occupying the Al3+ lattice with inversion symmetry, the ground state splitting of the 2Eg - 4A2g transition is reported and the decrease of the fluorescence lifetime with temperature is shown to be due to the increase in vibronic emission probability as well as increased probability of direct radiationless decay.

UV laser approach to Doppler tropospheric wind sounding from a satellite

The possibility of direct detection of tropospheric wind speed Doppler shift with an ultraviolet laser is considered. The use of the UV eliminates all practical concerns of eye safety, permits the use of uncooled detectors, and yields enhanced aerosol and Rayleigh backscatter signals. The Rayleigh signal, which in the free troposphere can exceed the aerosol signal by three orders of magnitude, is itself a candidate for wind speed measurement, despite the Doppler broadening of this signal. The basis of this approach is a diode-pumped, frequency-doubled alexandrite laser, which offers very high electrical to optical energy efficiency, an estimated 9%, in generating UV output. Efficiency is critical for a satellite based lidar system due to the size, cost, and mass of solar power generation and waste heat disposal subsystems. Pumping of alexandrite with 680 nm laser diodes has been demonstrated. Narrow linewidth, high spectral purity, and high frequency stability have been obtained with laser diode injection seeding of a ring alexandrite laser. The tunable diode laser control allows tuning of the laser for spacecraft velocity compensation. The potential performance of a wind sounding lidar scaled to match the 300 W power capability of a mid-sized satellite is evaluated for the extremely weak aerosol conditions of the southern hemisphere oceans. A 20 W output laser system, with 1 m aperture telescope, at 350 km altitude, may yield measurement precisions better than plus or minus 3 m/s through most of the troposphere, deteriorating to plus or minus 10 m/s under extreme conditions. A Rayleigh backscatter system will yield plus or minus 3 m/s precision to 8 km altitude, plus or minus 5 m/s at 15 km, even with zero aerosol content.

All solid state laser system, continuously tunable over 0.2-10 micron spectral range

An efficient room temperature all-solid-state laser system continuously tunable in the 0.2 - 10 micrometers spectral range has been developed. It is based on the alexandrite laser pumped LiF:F2+** color center laser system. The alexandrite - LiF:F2+** color center laser combination system has been shown to be a suitable drive source for a number of efficient nonlinear processes, including harmonic, sum-frequency and difference-frequency generation.

Sunday evening panel---Tunable solid state lasers

A panel discussion was held to review the development of tunable solid state lasers. Broadband vibronic laser materials, line switching and sharp line laser materials were discussed. Various applications of solid state laser technologies were reported. (AIP)

Advances in Lidar Transmitter Sources for Ocean-Atmosphere Remote Sensing

Pulsed, tunable alexandrite lasers in combination with harmonic generators and Raman wavelength shifter form a powerful and versatile tool for lidar (light detection and ranging) remote sensing. Such an integrated laser system can generate any wavelength from ultraviolet to infrared with the necessary beam qualities required for lidar measurement. This paper presents the development of injection seeded alexandrite ring lasers and linear cavity alexandrite lasers that can be deployed in ocean-atmosphere lidar remote sensing.

Improved laser light source for remote sensing of air pollutants by means of DOAS and DIAL

In this paper we discuss the potential advantages of the alexandrite laser as a light source for long range DOAS monitoring of air quality. The tunable alexandrite output can be frequency converted to provide essentially continuous coverage of the near UV spectrum. The wide tuning range and spectrally narrow output achieved by injection seeding are nearly ideal for several DOAS applications.