The traditional laser ranging technology, due to its superior directivity, monochromism and coherence, have been widely used in the precision measurement of absolute distance. However, Laser ranging with large size and high precision is susceptible to noise interference, and the measurement instrument lacks sufficient stability. In this paper, a non-optical interferometry has been proposed to measure 100 meters absolute distance. Moreover, a laser polarization controlling method, a laser frequency scanning technique and a heterodyne detector are designed to enhance laser feedback ranging signal and improve the low-frequency noise. The proposed study will serve as a valuable reference for large size and high precision absolute distance measurement.
Traditional locking techniques, such as PDH (Pound-Drever-Hall), HC (Hansh-Couillaud), spatial mode interference technique, offset sideband locking technique, quantum noise locking, etc., have been widely applied to laser frequency stabilization and precision optical interferometry measurement. Here, a new technique, which we call phase-sensitive heterodyne locking (PSHL), is investigated by use of frequency-synthesized light to obtain a phase-sensitive high-frequency photoelectric readout to lock the phase of a squeezed light. Comparing with above techniques, there are several kinds of advantages for PSHL to be advocated. Frequency-synthesized light, which allows arbitrary control of the amplitudes and phases of the modulation sidebands relative to the carrier, is derived by the AOM (acousto-optic modulator), not the EOM (electro-optic modulator). Interferometic signals coming from a balanced heterodyne detector are high-frequency AC photoelectric current which can easily get rid of low-frequency classical noise and lead to reach or break through the shot noise limit. A theoretical derivation of the PSHL error signal and the associated stability of the squeezed and anti-squeezed lock points will be carried out in this work.
Shot-noise-limited displacement measurement is difficultly realized by traditional optical interferometry for surface profile detection and MEMS (micro-electro-mechanical systems) manufacture, attributing to low sensitivity of Michelson interferometer and high classical noise of homodyne or direct detector. Aiming at above problems, a dark-end locking method is proposed to enhance sensitivity of phase detecting; a Mach-Zehnder interferometer is utilized to raise recycling efficiency of laser and a LO (local oscillator), dispensing with additional introduction, is obtained in reading out interferometric signal; a balanced heterodyne detector, leading to reach the shot noise limit, is designed to get rid of high low-frequency classical noise. This work will serve as a theoretical guide and experimental support for the forthcoming precision displacement measurement and sub-shot-noise audio-frequency laser interferometry experiments.
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