Length measurement method with resolution of picometer using high-finesse optical cavity and regular crystalline lattice

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A purpose of the research project is to develop a length measurement method with resolution of picometer, which is directly traceable to the meter definition, in order to promote the Nanotechnology. A change of an optical cavity can be measured with the change of the resonance frequency of the cavity using the beat frequency between the resonance laser and the frequency stabilized laser. And the change of the cavity can be also calibrated with a regular crystalline lattice. The following results are obtained.(1)Prototype of the optical cavity and the measurement system were developed. The one end mirror of the optical cavity is supported by the high rigid flexure stage, whose driving tool is a high power PZT actuator. Two mirrors, whose finesse are 400 and 1000, respectively, are used for the optical cavity. Resonance signals are detected with a lock-in detection method. The lock-in detection circuit consists of a microwave mixer and a microwave low-pass filter. A circuit and a saftware to detect and record the beat frequency were also developed.(2)Resonance feedback experiment was performed using the above experimental system. A frequency of the tunable laser diode can be tuned to the resonance frequency of the optical cavity using the above system. When the position of the one end optical cavity is changed, the displacement of the mirror can be determined from the shift of the resonance frequency. The results were compared with the laser interferometer. The measurement resolution of 0.1 nm or less can be achieved from the results.(3)The optical cavity whose finesse of 5000 or more was designated. With the optical cavity, we expect the resolution of 30 pm for the displacement measurement using the above system.