Abstract
A multi-wavelength diode laser interferometer for measurement of surface profiles has been developed. Three laser diodes emitting in the near infrared were used. The resulting synthetic wavelengths were approximately 14 µm and 290 µm. The long synthetic wave leads to a measuring range of ≈145 µm without counting the interference fringes. The result is used to determine the fringe order of the 14 µm synthetic wave and finally the fringe order of the optical waves within the measuring range. By modulation of the diode currents with different frequencies around 1 MHz, wavelengths are also modulated. The interferometer output contains harmonics of the modulation frequencies. Using a lock-in technique the interferometer signals from the three laser diodes are detected simultaneously with only one photodetector. For measurements of surface profiles the beams are focused on the sample. The surface is scanned by moving the sample in the x- and y-directions with mechanical translation stages.
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