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Test and Align optics
and Systems
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THIS IS A POWERFUL TOOL FOR TESTING IN APPLICATION AND RESEARCH AND DEVELOPMENT LABORATORIES AND FOR OPTICS FABRICATAOR SHOPS. SIMPLE AND PRECISE OPERATION PROVIDES FOR FAST VISUAL CHECKING OF INTERFEROGRAMS BY EYE, VIDEO CAMERA DISPLAY OR VIA FRINGE ANALYSIS.
The laser unequal pathlength interferometer is a portable, precision instrument for testing and aligning optical components and systems. It can serve as the primary inspection tool for in-process optical fabrication and final quality certification. It is very compact and portable, yet extremely stable and is adaptable to most component or system tests, including coated and uncoated optics in reflection or transmission.
The SORL LUPI Interferometer can easily be modified for phase shifting. For such an application a piezo operated flat can simply be placed and mounted in front of the permanent reference flat. The piezo induced phase shift in conjunction with the appropriate camera provides fringe analysis and interferogram interpretation.
This software supported fringe analysis system is available as an option. It permits mapping and averaging, wavefront scanning, fringe fitting, and subtraction of aberrations and polynomials.
Laser Unequal Pathlength Interferometer
The LUPI is a Twyman-Green type interferometer. In this type of instrument, light coming from the laser source is spatially filtered, collimated and passed through a beam splitter. Half of the light is reflected by the beam splitter and directed to a reference flat. The other half of the light passes through the beam splitter and is tightly focused. This focal point is also the focal point of an object being tested, such as a lens or a mirror.
After reflecting off the mirror being tested and reaching the reference flat, light is retro reflected. It retraces its path through the focal point and back to the beam splitter. In lens testing, beams collimated from the focal point also reach the reference flat and retrace their paths back to the beam splitter
At the beam splitter, the two beams of light recombine. Through constructive and destructive interference of the light waves, a pattern of light and dark fringes are formed. These are observed by the camera and fed to a video screen. The fringe pattern reveals the shape of the test piece and any errors that may be present. It can also be used to determine the focal length and off axis conditions.
The SORL LUPI Interferometer can easily be modified for phase shifting. For such an application a piezo operated flat can simply be placed and mounted in front of the permanent reference flat. The piezo induced phase shift in conjunction with the appropriate camera provides fringe analysis and interferogram interpretation.
This software supported fringe analysis system is available from DURANGO SOFTWARE. It permits mapping and averaging, wavefront scanning, fringe fitting, and subtraction of aberrations and polynomials.
Laser Unequal Pathlength Interferometer (LUPI)
Custom Instrument and Accessory Case
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· 2 mW laser, 0.6328 micron wavelength, polarized
· Fully adjustable x-y-z control — precise micrometer positioning
· Tests both focal and afocal telescope systems
· Compact, portable: 18" L x 10.1" W x10.1"H
(460 mm L x 260 mm W x 260 mm H)
· Weight: 47 lbs. (23 kg)
· Cone Angle Range: f/2 - f/8 Stand, (f/1 - f/20 optional)
· Microscope Objective Lens: 10X, V2, 0.25 N.A.
· Imaging Lens, Matched to Objective
· Objective Lens Extension Tube, 6" (150 mm) Long
· Eyepiece *
· Complete—Custom Instrument and Accessory Cases |
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Fringe Analysis System featuring DURANGO SOFTWARE
This is a powerful tool for testing in Application and Research and Development Laboratories and for Optics Fabricator Shops. Its simple and precise operation provides for fast fringe analysis. Permits quality control of most demanding optical components. Phase shift analysis can be routinely performed.
The contour map and phase height profile shown depict typical phase shift data obtained with a LUPI operating with a Fringe analysis system from DURANGO SOFTWARE
Calibration Sphere with Mount
(CSP™)
For calibrating the laser unequal pathlength interferometer:
· 2.5" (75 mm) Diameter, 2.5" (64 mm) Radius of Curvature,
l / 20 P-V (l = 0.6328 microns) Surface Accuracy
· Cell-Type Mount, Adjustable Tip and Tilt
*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.
Accessory Kit (AK-I™)
Permits measurement of cone angles from f/2 to f/20
· Microscope objectives (3), including interferograms
· Matching imaging lenses (5)
· Objective extension tubes, 4/10" (10 mm) to 3" (75 mm)
long (4)
· Eyepieces
Additional SORL components to create measuring systems.
· Flat Mirrors (Test Flats)
· Spherical Mirror (Hindle Spheres)
· Mirror Mounts
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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. The 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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