Charlie's Bath Interferometer

thingiverse

Bath interferometer designed to be constructed for under $100. I will soon add in the printable XYZ stage. Target audience is amateur telescope makers who want to quantitatively analyze their homemade mirrors using OpenFringe or other free software. Current suggested partslist (may change over time): Thorlabs ME05S-G01 - 1/2" Square Protected Aluminum Mirror, 3.2 mm Thick ($11.30 plus shipping) Surplus Shed L2046D - 15mm Coated 50/50 Cube Beamsplitter ($19.00 plus shipping) Surplus Shed PL1009 - 12.5mm dia. X 14.2mm FL precision coated BCX lens ($6 plus shipping) Red (650nm) Laser Diode ($1-3 depending) Possible cheap XYZ stages: Manual 3d printed based on http://www.thingiverse.com/thing:144838 DVD player DC 5v linear slider Mini Stepping Motor 2-phase 4-wire Stepper with linear rails e.g. http://r.ebay.com/RTt4zA Changelog: 2017-02-06 1111 Eastern - I'll soon be redesigning this in Fusion 360 aiming for easier printing, construction, and use. :) Stay tuned... 2016-10-26 1000 Eastern - Enlarged the tip/tilt mirror/prism adjustment post and the laser diode/pointer set screw holes. Added a 1/4" / M6 hole for mounting to XYZ stage. Various other tweaks and adjustments to hopefully aid in printing. 2016-10-21 0514 Eastern - First printing assembled. some kinks to iron out but seems like my design is on the right track. Typical case of it looks brilliant in CAD and tolerances were unrealistic especially for tiny screws and amount of stress thin ABS plastic can endure. Need to beef it up. 2016-10-19 1810 Eastern - Trimmed the edge of the lens holder completely off to allow for maximum unobstructed return laser beam.. improved design of mirror/prism tip tilt post with impressions for drilling to whatever size hardware you have available. Also added a small hole to allow for setting the laser pointer via set screw. Drill and tap to suit. Print Settings Printer Brand: Solidoodle Printer: Solidoodle 2 - Pro Rafts: Doesn't Matter Supports: Doesn't Matter Resolution: .2 Infill: 15% Notes: I plan to print in ABS with hexagon infill pattern for strength. Post-Printing Step 1 - Drill holes in mirror/prism tip/tilt post Drill three holes in the mirror/prism tip/tilt post. The first should be near the top of the mirror/prism support plate and will tip the mirror/prism forward if necessary. The second two holes should angle towards either end of the bottom of the mirror support plate. These will allow minor adjustments (ABS is somewhat flexible) to the mirror tilt/angle. Thread screws directly into plastic. It can be helpful to round the ends with a file. Step 2 - Mount the laser Remove laser pointer end cap and adjust lens stop with flat screwdriver until beam is well collimated. Best if lens internal to laser pointer is free from bubbles and defects. Insert into laser pointer holder and orient laser dot (if rectangular) at a 45 degree angle for best fringe contrast. Don't glue into place since it's helpful to be able to rotate the laser. You might add some teflon tape etc to create a snug fit. Use good common sense with your laser pointer and protect your eyes. Note: ensure the beam is exiting the cube beamsplitter roughly parallel with the interferometer base. Step 3 - Mount the mirror Using some double-sided tape mount the mirror to the mirror support as diagrammed. It can be helpful to place the cube beamsplitter in place and measure the beam separation until it is as small as possible while not being vignetted by the lens holder. Step 3 - Place the beamsplitter The beamsplitter is design to sit freely with no adhesive so that it can be rotated or shimmed to orient the beams perfectly. Set it in the recessed space such that the split is oriented at 45 degrees same as the mirror/prism (see diagram). Step 4 - Install the lens Insert the lens into the lens holder. If the fit isn't snug secure the lens in some manner. A later design will improve on the lens holder. Insert a screw into the interferometer base in the hole provided (drill as necessary) and slide the lens holder in place. Make note that the thin side should be on the right (mirror side)... this will prevent vignetting of the return beam. Step 5 - Follow the tutorials for Bath IF Helpful References: http://www.starryridge.com/interferometry/BathAnalysisV2.1.pdf http://atm.udjat.nl/tester/bathtester.html Comparison Between the Bath and the 4D 6000 Instantaneously Phase Shifted Interferometershttp://projects.imaps.aber.ac.uk/library/proj_162_375rp_12505.pdf