Abstract

A diode-pumped Nd:YAG laser source of long pulse length, sodium-resonance radiation is being developed for the purpose of generating a guide star in the earth's mesospheric sodium layer for astronomical adaptive optics. This laser will be similar to the two other laser sources of sodium resonance radiation previously developed at Lincoln Laboratory, one which produced as much as 0.6 J of sodium resonance radiation at a 10-Hz repetition rate and another which produced as much as 24 mJ at a 840-Hz repetition rate.¹ As in the previous laser sources, the sodium resonance radiation will be generated by sum-frequency mixing the output of a 1.064-μm Nd:YAG laser with the output of a 1.319-μim Nd:YAG laser (Figure 1). By operating the Nd:YAG lasers at wavelengths very close to the peak of their tuning curves as shown by the arrows in Figure 2, it is possible to match the wavelength of the sum-frequency radiation to that of the sodium D₂ absorption wavelength.² The laser system presently being developed will use diode lasers (rather than flashlamps) to pump the Nd:YAG (Figure 3). Diode laser pumping offers several advantages over flashlamp pumping including lower thermal loading of the Nd:YAG which results in improved beam quality, greater control over the temporal pulse shapes for improved sum-frequency mixing efficiency, and of particular importance for astronomical sites, greater electrical to optical efficiency, less heat generation, and less electrical noise generation.

© 1992 Optical Society of America