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LDDM uses an electro-optical device which detects the Doppler shift of a laser frequency caused by a moving target to measure displacement with a high degree of accuracy.
Conventional laser interferometers are based on the Michelson interferometer. There are two laser beams, the output beam and the return beam, which are parallel but displaced about 1", as shown in Fig. 1. Hence, large optics are required. Also, the alignment is critical, 3 elements have to be aligned on a parallel axis. The laser head is large and heavy, and a heavy tripod is needed to support the laser head. This approach requires critical and time consuming alignments, and requires additional expertise and expense to perform measurements.
The single-aperture MCV-500 laser system is based on LDDM technology. The laser head is very compact ( 2” x 2” x 8.5” or 50mm x 50mm x 216mm) and is completed with stabilization digital and analog circuits, electro-optics, and photo-detectors. As shown in Fig. 1, the output beam and the return beam are coaxial and share the same aperture. Hence large optics is not required and also a flat-mirror can be used as a target. Since there are only two elements to be aligned, the alignment procedure is much simpler.
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