Recent developments in laser-diode interferometry

Laser-diode (LD) interferometry based on heterodyne techniques is described. The developments covered include: sinusoidal phase- modulating, distance-measuring feedback and phase-shifting interferometry. The wavelength is controlled by the laser injection current and is continuously or stepwise changed to introduce a time-varying phase difference between the two beams of an interferometer with unbalanced optical path lengths. A feedback interferometer is described with electronics to stabilize the phase shift and to lock the interferometer on a preset phase condition by controlling the injection current of the LD. An automated phase-measuring interferometric system is developed in which the laser current is changed to synchronize intensity data acquisition with the clocks of a charge-coupled device. A typical experimental result shows measurements of the profile of a diamond- turned Al surface.