Analysis of multi-beam interference in heterodyne detection system

Shanjing Tao; Shenglai Zhen; Jian Fang; Xin Chen; Benli Yu

doi:10.1117/12.2667728

6 March 2023 Analysis of multi-beam interference in heterodyne detection system

Shanjing Tao, Shenglai Zhen, Jian Fang, Xin Chen, Benli Yu

Author Affiliations +

Proceedings Volume 12553, Fourth International Conference on Optoelectronic Science and Materials (ICOSM 2022); 125530R (2023) https://doi.org/10.1117/12.2667728
Event: 2022 4th International Conference on Optoelectronic Science and Materials (ICOSM2022), 2022, Henfei, China

Abstract

The Laser Doppler Vibrometry (LDV) system can measure parameters such as amplitude, velocity and acceleration of micro-vibrating objects. However, in the actual measurement process, in addition to the probe beam and the reference beam, as the surface roughness of the measured object increases and the diffuse reflectance decreases, the echo energy of the laser will decrease rapidly. This phenomenon can be extended to heterodyne detection systems. Due to the limitation of optical devices, the third beam (ie stray beam) caused by parasitic reflection is unavoidable. At the same time, the third beam has a certain intensity and phase distribution, which seriously affects signal demodulation of micro-vibrating objects. This paper analyzes the effects of multi-beam interference competition in heterodyne demodulation systems. Mathematical analysis shows that the interference competition depends on the signal amplitude, the interferometric light intensity ratio and the relative phase difference. Through mathematical derivation and simulation verification, the following conclusions can be drawn: when the relative phase difference is π rad, when the ratio of light intensity between the probe light and the stray light is controlled to tend to one, the simple harmonic motion with an amplitude of 1 nm is demodulated, and the amplitude can be observed to be nearly 200 times of the enhancement effect. For micro vibration with different amplitudes, the simulation shows that when the amplitude coefficient is π, the demodulation amplitude does not have amplification effect, and the amplitude coefficient is π can be used as the limit of demodulation amplitude amplification. This method has great application value in the high-sensitivity measurement direction of micro-vibrating objects.

Citation Download Citation

Shanjing Tao, Shenglai Zhen, Jian Fang, Xin Chen, and Benli Yu "Analysis of multi-beam interference in heterodyne detection system", Proc. SPIE 12553, Fourth International Conference on Optoelectronic Science and Materials (ICOSM 2022), 125530R (6 March 2023); https://doi.org/10.1117/12.2667728

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KEYWORDS

Demodulation

Vibration

Stray light

Heterodyning

Laser beam diagnostics

Distortion

Laser Doppler velocimetry

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