Multiplexed laser interferometer for non-dispersed spectrum detection in a dynamic flying height tester

An improved flying height tester (10) including at least two different-wavelength laser diodes (44, 45) that are time multiplexed through an optical system (58, 60, 66, 68, 72, 74, 76) to a measurement gap and having a photodetector (24) for measuring the amplitude of light reflected from said measurement gap through a pin-hole to determine the dimension of said measurement gap by light interferometrics, the improvement comprising:

• emission wavelength stabilization means (28, 29, 46-49) connected to each of said different-wavelength laser diodes (44, 45) for maintaining the respective temperatures of said different-wavelength laser diodes at a constant value, wherein the light emitted by each is maintained at a constant wavelength:
• emission amplitude stabilization means (28, 29, 50, 51) connected to each of said different-wavelength laser diodes (44, 45) for maintaining the respective light-output amplitudes of said different-wavelength laser diodes at a constant value:
• computer means (18) including calibration and test application software for interpreting signals received by included analog-to-digital connections (26, 32) to said different-wavelength laser diodes (44, 45) and said photodetector (24) into dynamic flying height measurements based on monochromatic interferometry phenomenon, and wherein the actual wavelengths of operation of said different-wavelength laser diodes (44, 45) are predetermined to provide ultimate measurement results that are substantially accurate;
• an aperture mask (78) in which said pin-hole is disposed and including a reflective surface surrounding said pin-hole and a partial reflectance mirror (76) the outputs a visual image (84, 86) of said measurement gap, wherein said pin-hole in said visual image marks a point of measurement;
• and
• a video camera (88) positioned to receive said visual image output (84, 86) reflected by the aperture mask (78) and mirror (76), wherein a video image marked by said pin-hole is obtained for manual targeting of a measurement.