Nanometric Vibration Sensing Using Spectral Processing of Laser Self-Mixing Feedback Phase

In this paper, a method is proposed to recover displacements with nanometric precision based on spectral analysis of the feedback phase self-mixing laser interferometric signal. This an enhancement previously developed called Time-domain Frequency-domain Signal Processing (TFSP) which could only target vibration(s) greater than lambda/8 amplitude (where lambda laser’s wavelength) so long as at least one vibration’s components has or equal lambda/2. Using TFSP reconstruction first approximation main displacement combined parameter (optical factor C and linewidth alpha) estimation, can provide better in-depth signal spectrum thus achieve detection even lower vibrations. Studies presented in paper indicate that does not require accurate estimation. Experimental results obtained using diode sensor = 785 nm show adding top allows vibrations down approximately lambda/32 average root-mean-square error 1.56 nm, corresponds 4 fold improvement over TFSP.