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
7 Stuart Road, Chelmsford, MA 01824
Telephone (978) 250-8640 Fax (978) 256-5605 E-mail to SORL