Develoment of Two-Wavelength Laser Precise Distance-Measuring Instrument for Earthquake Prediction

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In a laser distance-measuring instrument, there are several methods such as interformetric method, pulse method, and modulation method. To mesure medium distanced of one to fifty kilometers through atmosphere, the modulation method is most appropriate, which measures phase delay undergoing in traversing the distance. Terefore, a stable and efficient microwave electro-optic modulator must be developed for the accurate and precise measuement of distance through atmosphere by using the modulation method.A re-entrant cylindrical cavity using a KDP crystal is constructed which has a high laser intersity modulation index. An electro-optic modulator which operates at a frewuency of around 3GHz in the S-gand microwave regin is analyzed and developed for use in a laser distance-measuring instrument. A reentrant cylindrical cavity id consturcted by using a KDP crystal inside the caviry. %The cabity efficiency is theoreticaly analyzed by finite element method. The modulator has s laser intensity modulation index of 8% which has been obtained with a microwave input peak power of 1 W. The modulator is tested in the laboratory for distance measurement with the result that the modulator is capable of measuring a distance with the instrumental accuracy of imm.