Sample Tests with a LUPI
Concave Spherical Mirror Test: Concave spherical mirrors (MSP Series) from 4/10" (10 mm) to 6 ½ feet (2 meters) in diameter may be tested using the laser unequal pathlength interferometer with the proper diverging objective lens.
1. The focal point of the laser unequal pathlength interferometer objective is located at a distance coincident with the radius-of-curvature (rc) of the spherical mirror.
2. The resultant diverging wavefront from the laser unequal pathlength interferometer reflects off the spherical mirror back into the laser unequal pathlength interferometer, where the interference pattern is observed in the image plane, either:
· Through an eyepiece *
· On a ground glass screen
· On a video monitor (LUPI-IIA™ CM)
One
fringe of deviation indicates l/2 peak-to valley
(p-v) surface accuracy at 0.6328 microns, Helium-Neon laser light.
Off-Axis Parabolic Mirror Test: Interferometric analysis of an off-axis parabolic mirror is achieved using the laser unequal pathlength interferometer and a high quality test flat.
1. The laser unequal pathlength interferometer objective focal point is placed at a distance coincident with the focal length (fl) of the off-axis parabolic mirror.
2. The laser unequal pathlength interferometer objective projects a diverging point source to the off-axis parabolic mirror under test.
3. The off-axis parabolic mirror collimates the point source and projects it to the test flat.
4. The flat mirror autocollimates the light back to the off-axis parabolic
mirror that then focuses the light back into the laser
unequal pathlength interferometer
5. Minimal fine tuning of the laser unequal pathlength interferometer, off-axis parabolic mirror and test flat results in optimum interferometric analysis of the parabolic mirror surface (as the laser unequal pathlength interferometer and test flat are of known, calibrated quality).
Test configuration is conventionally known as double-pass autocollimation test.
Afocal Optical System Test: An afocal optical system, is analyzed for system wavefront using the laser unequal pathlength interferometer and a precision flat mirror. This double-passautocollimation test is performed as follows:
1. The laser unequal pathlength interferometer(minus objective diverger) and test flat are oriented such that the collimated laser unequal pathlength interferometer output strikes the test so that the collimated laser unequal pathlength interferometer output flat at normal incidence.
2. T'he afocal system, in this case a telescope, is placed in the optical path and aligned so that the collimated LUPI-IIA™ output transmits through the telescope to the flat. The flat then reflects the beam back through the telescope to the laser unequal pathlength interferometer.
The interferogram produced by the laser unequal pathlength interferometer is examined, with one fringe of deviation equal to l/2 P-V system wavefront error.
* Space Optics Research Labs does not recommend the classic "View with an eyepiece"approach. Possible eye damage may occur when using an eyepiece to observe interferograms. Observe proper laser safety practices. Eyepieces are supplied for image projection not visual use.
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