A 20-W all-solid-state continuous-wave single-frequency source tuned to the sodium D2a line at 589.159 nm has been developed for adaptive optical systems. This source is based on sum-frequency mixing two injection-locked Nd:YAG lasers in lithium triborate in a doubly resonant external cavity. Injection locking the Nd:YAG lasers not only ensures single-frequency operation but also allows the use of a single rf local oscillator for Pound-Drever-Hall locking both the injection-slave and the sum-frequency cavities. We observe power-conversion efficiencies in excess of 55% and a linearly polarized diffraction-limited output tunable across the sodium D2 line (589.156 to 589.160 nm) with no change in output power and with high amplitude and pointing stability.

We have demonstrated a remote magnetometer based on sodium atoms in the Earth's mesosphere, at a 106‐km distance from our instrument. A 1.33‐watt laser illuminated the atoms, and the magnetic field was inferred from backscattered light collected by a telescope with a 1.55‐m‐diameter aperture. We theoretically predict a shot noise limited measurement sensitivity of 190.25emnT/Hz. The measured sensitivity was 1620.25emnT/Hz due to a smaller returned intensity and smaller resonance strength than expected. The value of magnetic field inferred from our measurement is consistent with several models of the Earth's field shape to within a fraction of a percent. Projected improvements in optics, plus the use of advanced lasers or a large telescope, could result in 1‐nT/Hz sensitivity.

ABSTRACT. Measurements of a laser-pumped sodium guide star produced over the Starfire Optical Range in 2002 November show that the brightness of the spot produced by 11.5 W of linearly polarized power on the sky was equivalent to a mag star. However, taking into account that the transmission through a V filter V p 8.0 is only 55% at the wavelength of sodium, its corrected magnitude, , was 7.4, or 800 photons s Ϫ1 cm Ϫ2 at the V 1 top of the telescope. In 2003 March, tests with linearly and then circularly polarized beams out of the telescope showed that a circularly polarized beam from 12 W of power out of the telescope produced a spot with V p 1 (1015 photons s Ϫ1 cm Ϫ2 at the top of the telescope), 0.7 mag brighter than a linearly polarized beam from 7.1 11.1 W of power out of the telescope. Over the 4 nights of experiments over two seasons, the apparent 2j width of the spot varied between 3Љ .6 and 4Љ .6, or 1.6 and 2.0 m at 92 km altitude, and its length through the sodium layer was 4.6-8.5 km, but no variation of spot size with power on the sky was seen.

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Stress-induced birefringence in cw-pumped Nd:YAG rods create stability limitations on the TEM(00) polarized mode of a resonant cavity. We present and verify experimentally a thermo-optical model describing a ring cavity containing a birefringent cw-pumped Nd:YAG rod. We use the model, along with experimental evidence, to show that a fundamental TEM(00) mode size and pump-power limitation exists for any cw-pumped Nd:YAG laser, implying a maximum allowable TEM(00) output. We show that the largest TEM(00) mode radius that can be supported in the rod is approximately 1.1 mm and is independent of the physical size of the rod.