Photo Gallery

From Starry Ridge

This page contains photos of interferometers, interferometry-related equipment, and interferograms. If you add a photo, please include some text describing the photo.

1 Steve Koehler's Prototype Bath Interferometer
2 Bath by Dennis Faith
3 Other Configurations
4 Fourier analysis of interferograms and Air Currents captured
5 Laser pointer beams
6 Dave Rowe's Inexpensive XYZ Stage
7 Inexpensive Wooden position-er by Dale Eason

[edit] Steve Koehler's Prototype Bath Interferometer

This is my prototype Bath interferometer stuck together with double-sided tape and duct tape. The 15mm cube, the small mirror, and the 10mm fl lens from Surplus Shed. The aluminum parts holding the diagonal and lens were fashioned using a hacksaw, file, and hand-held drill. The laser is an inexpensive, red laser pointer. Although this shows fringes very well when used visually (with the laser in non-lasing mode), the tricky part is image capture. I have not had much luck, yet, with a webcam. I did better with a digital camera.

This interferogram was taken using a Canon A80 camera using its remote capture capability. This method of image capture is less than ideal, because of the lack of focus control, and the fact that the image shown on the screen is too small to show fringes clearly.

[edit] Bath by Dennis Faith

This has an oversized xyz stage that started life as a Foucault stage. THe Bath implementation is the right angle version. Like Steve Koehler's above. The right angle prizm has a front surface mirror on its hypotenuse. The camera to capture igrams would be placed behind the beam cube beam splitter.
Back view
Front View

[edit] Other Configurations

Bath interferometer using a prism for the right angle mirror. All optical components except laser from surplus shed. Vesta webcam lens replaced by 25mm fl lens from Edmund Optical. The Vesta threaded lens mount has enough back focus to accommodate the long back focus lens. Dale eason

Update: I found this version very hard to align the beams parallel, prone to getting fingerprints on the surfaces during aligning, and hard to clean. The fringes were very low quality with much noise. I think part of that was caused by the side prism having more surface involved than a front surface mirror would. I was not happy with the results and have scrapped the design. Dale eason 00:04, 20 February 2007 (EST)

This Bath interferometer uses the laser at 90 deg to the optical path. This allows the camera to be placed behind the cube and pointed at the mirror through the cube.

The beam splitter and side mirror are epoxied to the top of metal pegs and can be rotated about the peg axis. This helps in initial setup. Also the beam splitter and side mirror can be easily removed for cleaning. A set screw for the beam splitter peg can be seen protuding from the back of the interferometer. The metal pegs can best be seen in the back view. This is my second version of a Bath interferometer and I like it best so far.

Dale Eason

Front view

Back view

Another example and the camera would look into the back of this one.

Bath configuration using port W2. This assures even beam intensities and good contrast at the expense of more surfaces to cause noise.

Fringes captured at Port W2 exiting from the front of the cube on the right hand side of the picture. Taken with a Nikon D40 and 50mm F2 Lens at 1/200 sec.

[edit] Fourier analysis of interferograms and Air Currents captured

These pictures were processed from high resolution many line igrams using Fourier Analysis method. It creates an artificially bumpy surface that can be removed by averaging many igrams. That has not been done here. Ring like bullseye at 7 o'clock is the result of diffraction around dirt in the system it can be seen best in the left image. The two tiny peaks in the center are caused by the mirror center paper collimation ring.

No appreciable air currents.

Air currents create a wall cloud at the top of the mirror and a few billows other places

[edit] Laser pointer beams

Here are three different laser pointers. These images were all taken at the same camera setting. The laser was shown through a magnifyier onto a white wall.

The left one is the best of the group. It is the brightest and largest with the most even illumination. This particualar pointer has the beam off center and part of it is obscured by the housing on the left side. It would still be usable. The middle pointer has a very narrow beam and has some ring structures in the middle. The pointers shown in the middle and right images do not have even illumination. Some lasers have a very spongy center that look like the left side of the left image. Those would create very spongy interferograms. If you have a choice use a pointer like the one on the left.

[edit] Dave Rowe's Inexpensive XYZ Stage

A very inexpensive three axis positioning stage was made for less than 10 dollars in materials. Total fabrication time was less than three hours.

The following image shows the starting materials: A wooden dovetail drawer slide, springs, knobs, 6-32 screws and some miscellaneous plywood.

All assembly was performed with wood glue. The following image shows the stage as it was being assembled. Parts were held in place with masking tape while the glue dried.

The following two images show the final, assembled stage. It works quite well.

[edit] Inexpensive Wooden position-er by Dale Eason

If you can drill parallel holes easily then this stage is very easy to make. It uses 1/2 solid core plywood, 8-32 screw. 1/8 diameter drill rode or music wire and a small knob. The smaller stage in front used solid walnut but the plywood will have better dimensional stability. Several can be combined to make a small x,y,z stage.

To reduce friction the sliding parts can be drilled with a 5/32 inch drill and then 1/8 inch ID brass tube from K&S can be pressed into the holes. The tubing is usually available at hardware and hobby stores in the US.