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5Laser speckle-vibrometer for detection of transverse and angular displacements
A.I. Trikshev*, V.A. Kamynin, V.B. Tsvetkov
Prokhorov General Physics Institute of the Russian Academy of Sciences, Vavilov St., 38, 119991,
Moscow, Russia
* trikshevgpi@gmail.com
Laser speckle vibrometry is a modern technology for remote measurement of mechanical vibrations of objects [1-4]. The main advantages of the measurement method include: remote and non-contact measurement of vibration; no influence on the resonance properties of objects; no preliminary preparation of the object surface is required. The main advantage of this method is that the speckle pattern is formed in the whole space around the scattering object. This pattern can be observed both at zero angle to the surface and at large deviations from the normal. Specificity of the measurement technique allows to carry out measurements both at short distances (less than a meter) and at long distances (tens of meters) due to the adjustment of the optical system.
The setup used a single-frequency semiconductor laser diode with a 976 nm wavelength. A monochrome camera with a lens with a focal length of 100 mm was used as an image receiver. Linear translation stage and mini rotation stage were used to realize the displacements. The screen was installed on a stage. The distance from the screen to the speckle vibrometer was more than 2.5 m. Figure 1 shows speckle patterns obtained when the screen was moved transversely by 0.1 mm. The short line indicates the original position of the line.
a) b) c) d)
Fig. 1. Speckle patterns a) before and b) after transverse movement of the screen by 0.1 mm; c) difference pattern of two adjacent frames, d) difference pattern of frames before and after the displacement by 10 ^m.
Difference patterns were used to register movement over a distance of 10 ^m (Fig. 1 c,d). This is because the image displacement on the matrix was less than 1 pixel. With optimization of the optical system and more careful mathematical processing of the data, a movement of 1 ^m could be recorded. In Fig. 2. speckle patterns obtained at an angular screen offset of 0.001 rad are presented.
I II
Fig. 2. Speckle patterns obtained when the screen was moved angularly by 0.001 rad.
As a result, transverse displacements up to 1 ^m and angular displacements up to 0.001 rad at distances greater than 2.5 m were recorded. However, according to the data obtained for angular displacements it follows that with additional processing it is possible to determine angular displacements better than 10 - 4 rad.
[1] H. Hong, J. Liang, L. Deng, W. Guo, X. Wang, Optics Letters, vol. 48, p. 3837, 2023.
[2] M. Sheinin, et al, Proceedings of the IEEE/CVF Conference on Computer Vision and Pattern Recognition, p. 16324-16333, 2022.
[3] X. Huang, et al, Optics & Laser Technology, vol. 148, p. 107759, 2022.
[4] N. Wu, S. Haruyama, Sensors, vol. 21(9), p. 2938, 2021.
