Mitigating speckle noise in a laser Doppler vibrometer using Fourier analysis

We propose two strategies for eliminating the speckle noise in a laser Doppler vibrometer according to Fourier analysis. Fourier transform is theoretically conducted on the speckle pattern phases, whose variation dominantly contributes to the speckle noise. The calculated and experimental frequency spectra of speckle noise both present oscillations of the frequency series (frequency peaks have constant intervals). (1) A low-pass filter can remove the noise if the vibration frequency is far lower than the first frequency peak of the noise. (2) The vibration energy can be revealed by removing the oscillating frequency trend. Physical experiments demonstrate the effectiveness of both despeckling strategies.