We report on the generation of over 900 mW of tunable cw light at 780 nm by single pass frequency doubling of a high power fiber amplifier in a cascade of two periodically poled Lithium Niobate (PPLN) crystals. Over 500 mW is generated in the first crystal. In the limit of low pump power, we observe an efficiency of 4.6 mW/W2-cm for a single crystal, and 5.6 mW/W2-cm for a combination of two crystals, with an enhancement of the doubling efficiency observed with two crystals due to the presence of second harmonic light from the first crystal acting as a seed for the second. We have frequency locked this laser source relative to a rubidium D2 hyperfine line and demonstrated its utility in a sophisticated laser cooling apparatus.

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The Shuttle Radar Topography Mission (SRTM) is an interferometric synthetic aperture radar system that flew on the space shuttle in February 2000. SRTM has an inboard antenna in the shuttle cargo bay and an outboard antenna at the end of a 60-m mast, extending from the cargo bay. In order to meet the elevation mapping accuracy requirement, the relative phase delay between the radar signals received via the outboard channel, compared with the inboard channel has to be known to within 8 at 5.3 GHz. This paper describes the design solutions and constraints, the devices, the analysis, and validation used to implement an optical calibration loop for SRTM. The calibration method involves injecting a tone into one panel of the inboard antenna, and sending an optical copy of the tone via a fiber-optic cable to be injected into the outboard antenna. A portion of the optical signal is reflected off an outboard partial mirror and travels back via the fiber to the inboard calibration system. There, it is converted back into a radio frequency tone and its phase is compared with the phase of the original tone. As the temperature of the mast fiber changes, a phase error is detected in the phase comparator. This error is used to control a custom designed optical phase shifter connected in series with the mast fiber. This phase-locked-loop guarantees that the phase of the calibration tone at the outboard stays within 1 relative to the phase of the calibration tone at the inboard antenna.