APPLICATIONS

    Once the “only game in town,” the dominance of the ruby laser has diminished in years following the discovery of more efficient lasers such as the YAG. The primary applications for ruby lasers nowadays are research lasers and as sources for holography. The double-pulse ruby laser, for example, is used to record deformation of a test material by using each of the two closely spaced pulses to record a holographic image. Any deformation or movement is recorded as an interference pattern between the two images.

         One military application (which has now been replaced by newer technology) is the U.S. M-60 tank rangefinder, in which a compact ruby laser was used to produce  fast, narrow pulse of light which could be reflected from a distant target to determine the range by measuring the time of flight of the laser pulse to the target and back. This laser, perhaps one of the smallest commercial ruby lasers built, consisted of a small ruby rod (8 mm in diameter by 75 mm in length) pumped by a linear flash lamp driven with 125 J of energy supplied by a small capacitor and pulse-forming network. A unique aspect of this laser was the rotating-mirror Q-switch, in which one cavity mirror was spun at 30,000 rpm by an internal motor. A magnetic pickup coil sensed the mirror position and triggered the flash lamp just before cavity alignment occurs in a scheme similar to the manner in which most automotive engines sense camshaft position in order to fire spark plugs at the appropriate time. A delay could be imposed by an electronic circuit to optimize the pulse energy before the cavity became resonant and oscillation occurred. This small laser had an output energy of 50 mJ, and since the entire assembly was air-cooled, repetition rates were low.