| 摘要 |
To measure distances, light from a flash tube is plane polarized by a polarizing filter, then polarization modulated by an electro-optical crystal, then passed along a 'wobbling' light path, then subjected to a relative retardation of about a quarter wavelength by a rhomb and then passed through a calibrated variable light path before being projected to a distant target reflector. The reflected light returns along the same path and is detected by a photomultiplier after passing through the polarizing filter. Adjustment of the variable light path until a null is obtained at the photomultiplier indicates that the length travelled by the light from the crystal to the reflector and back is an integral number of modulation wavelengths, possibly plus one half-wavelength. The quality of the null is adjustable by adjusting the orientation of the rhomb. Temperature correction may be provided by constructing a reference resonator defining the modulation wavelength of the same material as a structure being measured.
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