The scanning slit method uses one or more slits that pass through the laser beam in front of a large area detector. The signal from the detector is proportional to the beam profile. Since the slit admits only a small fraction of the laser power onto the detector, this method allows for the direct measurement of unattenuated high-power beams.
As shown in the NanoScan diagram below, two precision slits are mounted at right angles to one another and at 45 degrees to the scan plane of the drum. One slit moves through the narrow axis of an elliptical beam, giving narrow width profile, while the second slit measures the wide profile of the elliptical spot. This simple invention allows sampling two cross-sectional irradiance profiles providing orthogonal beam positions to the micron level. Because the drum radius of each slit is precisely controlled to within microns, users with shallow depth-of-focus beam waists can be confident of accurate measurements.
The scan head contains a motor mount, a small DC motor, encoder, and slit apertures mounted on a spinning drum. The super-quiet motor is specified with high precision bearings to ensure excellent position measurements and long life. A rotation mount allows scan head rotation about the entrance aperture, providing an easy way of aligning the scan head with the axes of elliptical beams.
