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The kit includes the following:
CAUTION: Mirror coating on highly curved surface is extremely delicate. DO NOT TOUCH. These should be clean, requiring at most to have dust blown off with a air bulb. If cleaning is needed, ONLY use laser mirror cleaning techniques! Warranty does not cover damage to mirror surface! I suggest NOT removing the mirrors from the lens tissue until read to use. They are just mirrors! :)
When set up in the confocal configuration where the mirror spacing is equal to the RoC, the Free Spectral Range (FSR) will be approximately 1.75 GHz. The mirror set can be used for other mode degenerate SFPI configurations using different spacings if desired, but the common confocal setup is generally most useful. This is left as an exercise for the student. More info at Mode Degenerate Fabry-Perot Interferometers.
The PD can be connected via shielded cable directly to the vertical input of your scope with a 10K ohm load resistor. However, it is better to connect the PD in series with the load resistor and back-bias it with a few volts (e.g., a 9 V battery). With back bias, the response (across the load resistor) will be linear up to several mW.
Confirm that the PD is responding to light. Room light will suffice, but a better test source is a dimmable LED flashlight. These use Pulse Width Modulation (PWM) to chop the light output and a pulsed waveform should be clearly visible on the scope.
For initial setup, leave the entire photodiode uncovered. Once there is a signal, installing an aperture to block all but the centeral 1 mm or so will improve resolution. For low power lasers, a preamp may be required.
The diagram below shows just one example of a suitable design. This is close to the minimal complexity and cost possible using Home-Depot hardware and scrap parts. The other extreme is to use Newport or Thorlabs optical breadboard components. But if you can afford those, you may not need to be messing around with this kit!
A pair of mounts for 1 inch optics would be best. Use an adapter (available from Thorlabs) to install one of the mirrors in its mount. Attach this to a linear slide on a baseplate with a micrometer adjustment. Glue the other mirror to the PZT center using 3 dabs of 5 Minute Epoxy. DO NOT USE SUPERGLUE!!!!! Once the adhesive has cured, attach the PZT to the other mirror mount so it contacts only around its perimeter (to allow the center to move). Use an insulating pad and fasteners if it is to electrically float. Attach this mount to the baseplate with a spacer (if needed) so the centers of both mounts are precisely in-line.
A focusing lens with a focal point roughly in the center of the cavity (shown in the diagram but not included in the kit) may improve performance under some conditions but is not essential.
More likely, the peaks will be smeared out or composed of multiple small blips as in the sequence of graphics below. Or there may be nothing. Adjust the spacing of the mirrors in small increments Slowly and then then let it settle down. With any movement, the display will become quite scrambled, so be patient. If going one way makes it worse, go the other way. :) If the initial cavity spacing was within about 1 mm of being optimal, there should be only one place close by where it resolves into a beautiful display like the one above. ;-)
The entire sequence would represent a length change of a fraction of 1 mm. The amplitude of the single peak (in this SLM example) would actually increase by a larger amount than shown. Some of these diagrams are from the Toptica SFPI 100 manual, I hope they won't mind. :)
First time users do not appreciate how precise the spacing needs to be. But it's less than 1/10th width of a human hair - a few microns. Once close, the only effective way of fine tuning it is with precision screws that change spacing such as would be found in a linear translation stage, a 3-screw pan/tilt mount, or something equivalent.
It's also essential to avoid back-reflections into the laser, which will likely destabilize it and create chaos in the display. The alignment should be adjusted such the the reflections from the SFPI (mostly the front mirror) do NOT enter the laser's aperture. With the confocal cavity SFPI, a slight offset will not significantly affect resolution. Ideally, an optical isolator could be used but they are pricey.
Using mirrors identical to the ones in the kit, I've seen a finesse at 633 nm of 500 or more, though this depends on all the stars aligning perfectly. :) And I can't guarantee that all samples are that good. But expect a finesse of several hundred with reasonable care. Performance at other wavelengths may not be as good but it should still be usable to below 594 nm (yellow HeNe) and above 650 nm (may actually be better at longer wavelengths).
For more on SFPIs, see the section: Scanning Fabry-Perot Interferometers of "Sam's Laser FAQ".