Correlation-based speckle velocimeter with self-mixing interference in a semiconductor laser diode

We propose a novel self-mixing laser diode speckle velocimeter based on aut ocorrelation. The self-mixing laser diode launches and receives reflected l ight from a moving surface that has a random reflection profile. Some porti on of the scattered light backcouples into the laser cavity and causes rand om intensity variations in the form of speckle signals. These speckle signa ls obtained from a self-mixing laser diode are processed by use of autocorr elation. The Linear relation between the velocity and the reciprocal of the correlation time of the speckle intensity fluctuations allows us to determ ine the velocity easily if proper calibration is performed. The range of th e investigated velocity is 20-450 mm/s. For an aluminum target that moves a t a velocity of 350 mm/s, the measurement error is less than 2%. (C) 1999 O ptical Society of America OCIS codes: 120.7250, 030.6410.