J.K. Erwin Corporation

Optical Instrument Design and Fabrication

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Introducing the SBSI

For special design and pricing information, contact Raymond Castonguay, Engineering Synthesis Design, Inc. www.engsynthesis.com, PO Box 18126 Tucson AZ 85731-8126, USA, Phone 520-296-3068, Fax 520-296-2897 Email: rjc@engsynthesis.com

 

The Small Beam Shear Interferometer allows quick adjustment of focus, coma, astigmatism and spherical aberrations in laser optical systems and collimated laser diodes. Custom designs are available for laser beam diameters from 1 to 8 mm, and for wavelengths from the mid-UV to near IR.

The SBSI is a small beam lateral shear interferometer that uses a proprietary (patent pending) optical technique to shear the beam without using a conventional shear plate, so there are no limitations in beam size due to constraints on shear plate thickness. We have successfully built custom systems for beams less than 1 mm in diameter. The sheared beam image, with fringes in the overlapped region, is magnified and projected on a camera CCD array, ground glass or fluorescent viewing screen. Optical aberrations can be identified and corrected while viewing the SBSI fringe pattern. For example, coma can be corrected by changing the tilt of a collimating lens in an optical system so the fringes on the SBSI change from curved to straight. A reference line on the SBSI screen indicates the best focus (collimation) angle for the fringes. When the fringes are parallel to the SBSI reference line, all optical aberrations are minimized. Beams can be checked directly or in reflection using a rotating beam-splitter cube mounted on the front of the SBSI.

Focus alignment sensitivity is approximately 170 micro radians of beam divergence, corresponding to 3 degrees rotation of the fringes for 3 1/2 fringes. Each SBSI is optimized for 3 1/2 fringes for a specific wavelength and beam diameter, but every SBSI can be used to check beams over a certain range of wavelengths and diameters. Please inquire about special SBSI designs that are optimized for your application.

 

Typical SBSI Applications

        Alignment of optics using a 355 nm UV beam in laser mask pattern generation systems. Use of the SBSI reduced alignment time for some subassemblies in these systems from days to hours.

        Alignment of optics in dynamic testbed instruments for characterizing MO, DVD, CD and phase-change optical data storage media. These instruments use collimated laser diodes from 390 nm to 780 nm. The SBSI allows fast alignment of the optics, and easy visibility in the UV.

        Alignment of laser diode collimators and anamorphic prism pairs.

        Alignment of holographic optical data storage instruments.

        Characterization of optical flats, beamsplitter cubes and windows.

        Alignment of optics in disk mastering systems.

SBSI Images

The following images were made with DIFFRACT software, http://www.mmresearch.com. These computer-generated images perfectly simulate the SBSI interferometer display, and give an idea of the sensitivity of the SBSI to various aberrations in a beam.

 

From left to right, no aberrations (perfect focus), .25 waves of defocus (diverging beam), and -.25 waves defocus (converging beam).

 

.25 waves of spherical and -.25 waves of spherical.

 

.25 waves of coma at 0 degrees, and -.25 waves of coma at 0 degrees.

 

-.25 waves of coma at 90 degrees, .25 waves of coma at -90 degrees, -.25 waves of coma at -90 degrees and .25 waves of coma at 90 degrees.

 

.25 waves of astigmatism at -45 degrees, .25 waves of astigmatism at 0 degrees, .25 waves of astigmatism at 22.5 degrees.

 

.25 waves coma and .25 waves spherical at 0 degrees, .5 waves coma and .5 waves spherical at 0 degrees, and 1 wave of spherical.

 

3 waves of spherical and 5 waves of spherical.

 

2 waves of spherical at 400 nm, using the SBSI fluorescent screen.

 

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For special design and pricing information, contact Raymond Castonguay, Engineering Synthesis Design, Inc. www.engsynthesis.com, PO Box 18126 Tucson AZ 85731-8126, USA, Phone 520-296-3068, Fax 520-296-2897 Email: rjc@engsynthesis.com