Development of an optical probe for profile measurement of mirror surfaces

An optical probe for profile measurement of mirror surfaces is developed. This probe, consisting of a displacement meter and an angle meter, can detect the displacement and surface slope at one point simultaneously. Both the displacement meter and the angle meter of the probe employ position-sensing detectors (PSDs) as detecting devices. An optical fiber output is used as the light source so that the probe is made compact and has good characteristics. To eliminate influences of light disturbance the light intensity of the light source is modulated by a sine wave of 20 kHz, and only the position signal is removed from signals obtained from the PSDs. Calibration results show that the displacement meter and the angle meter can measure larger than ±500 μm and ±60 arcmin with good linearity, respectively. Estimating from the SNR of the system, the displacement resolution and angle resolution are ±10 nm and ±0.1 arcsec, respectively.