COHERENT LASER RADAR AT 1.06 MICRONS USING SOLID-STATE LASERS (AMPLIFIER, SINGLE MODE FIBER)

A coherent pulse-Doppler radar system has been constructed using the 1.06 (mu)m laser transition of Nd:YAG. The construction and operation of this system extends by one order of magnitude the range of frequency over which coherent radar techniques have been applied. Technical advances making this extension possible include the development of a stable single-mode nonplanar ring laser oscillator, a high-gain linear amplifier, and the use of single-mode optical fiber for beam handling and mixing.; The operation of the nonplanar ring oscillator is analyzed using Jones matrices. When pumped by a 200 mW laser diode array, the oscillator reached a single-mode output of 24.5 mW. The frequency stability, as established by mixing with an independent oscillator, was (+OR-)1.5 kHz over a period of 10 msec.; The multiple-pass amplifier provided gain of 62 dB using four passes through a single zigzag slab of Nd:YAG. The extractable energy from the slab was limited to 12 mJ. The surface tolerances on a zigzag slab are demanding if good wavefront quality is required.; Fiber optical components were used to direct and mix the signal and local oscillator radiation to achieve efficient heterodyne detection. The reliability and flexibility of single-mode fiber simplified the process of alignment and signal detection.; Solutions to problems of feedback and interference that occurred during system integration are described. The completed system was tested by making range measurements of clouds at 2.7 km and aerosols at 600 m. The fundamental advantages or disadvantages of short wavelength radar depend strongly on the particular measurement problem. The technical advantages of a laser radar system based entirely on solid-state components are compactness and reliability.