Temperature Invariant Laser Interferometer Position Sensor
Original Publication Date: 1988-Mar-01
Included in the Prior Art Database: 2005-Feb-14
As seen in Fig. 1, motion of the retroreflector R along the optic axis causes alternating constructive and destructive interference (fringes) to be detected at the photodiode D. The number of fringes counted at the photodiode indicates the relative motion of the retroreflector. Theoretically, a shift in the wavelength of the laser, while the retroreflector's position is fixed, should also cause fringes at the photodiode. Thus, a shift in the lasing wavelength indicates false motion of the retroreflector. The operation of GaAs lasers is sensitive to the temperature of the laser. As shown in Fig. 2, the lasing wavelength increases as the laser operating temperature increases. Two types of change in wavelength are shown: (Image Omitted) 1. Region 1 represents a longitudinal mode hop.