Laser interception technique with heterodyne self-mixing interferometry

Laser interception technique is a precision measurement technology which takes advantage of laser interferometry to detect weak vibrations caused by acoustic excitation with high precision. It has been greatly valued by national intelligence agencies, with pervasive application to counter-terrorism, crime investigation and other national security and defense affairs in various countries. This paper proposes an interception scheme based on acousto-optic frequency shifting laser self-mixing interferometry. In the case of weak light, the vibration information of the target object could be acquired in real time with high precision. And it is applicable for the development of miniaturized laser interception equipment. We use self-developed acousto-optic frequency shifters to stabilize the heterodyne frequency of the two laser beams at kHz level and heterodyne beat signal as carrier signal for micro-displacement detection. Besides, the self-balanced detection technology is applied to eliminate the common-mode noise of detection system, so as to ensure the signal-to-noise ratio of weak signal detection at nano-watt-level of laser power under long-distance interception conditions. By means of modulation phase recovery technique, combined with cavity frequency modulation method, Fourier transform phase extraction principle and Kalman filter method, the program realizes high-precision recovery of self-mixing interferometric displacement under weak feedback conditions and can effectively suppress low-frequency noise of laser source.