Optical Cement: Fill & Download for Free

Green lasers are especially susceptible to misalignment from being dropped. Other lasers are more simple and might be fixed if you know a lot about optics and have micro-positioners in your hobby box.Green lasers I am afraid take way too much skill and knowledge to fix. Maybe you will find a sympathetic laser engineer to work on it. It consists of a 0.808 micron pump diode and a piece of yittrium-aluminum garnet or YVO4 doped with neodymium. There is a resonator around this crystal. The resonator needs to stay aligned to within a fraction of a milliradian and the infrared pump beam must be aligned to the YAG. Also, inside the resonator is a lithium niobate or KTP crystal which must be aligned to even tighter specs to do the nonlinear conversion from the 1.064 micron fundamental wavelength to the 532 nm green wavelength. Then the beam has to be focused. You will need very special equipment to work on that. There is a very tiny expanding lens and there is a tiny collimating lens. These must be positioned to very tight tolerances. If the module is deformed in a fall, you are out of luck.Simple lasers that are based on a laser diode module have a toric collimating lens, or more often a small anamorphic beam expander to get the beam roughly circular.The lenses need to be placed within about a thousandth of an inch of the right positions. You can’t possibly do it by hand. You need to put them in place with the micro-positioners, and cement them in place using clear index-matching optical cement cured with UV light. After curing you can remove the micro-positioners This is not a beginner project, but a skilled do-it-yourselfer can manage.

Prisms have certain advantages but I wouldn't say unilaterally that they are better. Perhaps one of the biggest advantages is that the prism reflects by total internal reflection, which is very close to 100% reflection whereas the metalized mirror might achieve 95 or 96% reflection. This advantage is offset by the fact that the prism has two entrance faces, each of which can suffer a few percent loss unless a very sophisticated anti-reflection (AR) coating is used. If you're going to use a sophisticated AR coating on the prism that you could consider a very sophisticated reflection coating on the mirror that could get your reflectivity above 99%. So using modern coatings the mirror and the prism are about at parity.In order for mirrors or prisms to reflect without distortion both of them need to be very robustly made. Prisms are inherently robust whereas mirrors are only robust if they are made very thick. Of course in a high-quality Periscope made of mirrors they would be made thick and very flat.The AR Coatings on the prism are likely to be more environmentally robust than the metallic reflecting coatings on a mirror. This is because the AR coatings are dielectric and are more robust to corrosion than metals. Of course if the coating on the mirror is also dielectric, which would be necessary to achieve the greater than 99% reflectivity, then this advantage becomes moot.The final issue is maintaining critical alignment by mounting. The prism is inherently robust and with three optical surfaces it is easy to register optically and mechanically. The mirror has only one optical surface but if it is made robustly it can also be optically registered and mounted.Finally, if the periscope is short, the prisms can be optically cemented to each other for alignment, the way they are optically cemented in binoculars. But most periscopes have a significant distance between the two bends in the optical path so this advantage seldom applies to periscopes.Traditionally periscopes have been made with prisms but there is no reason that a high quality periscope could not also be made with high-quality first-surface mirrors. Such a telescope may have certain advantages over its prism-based counterpart, such as lower weight if weight is a concern such as for aerospace.I once designed a periscope for use inside a nuclear reactor. This was a very long, very high performance periscope with multiple bends in the optical path. This periscope used mirrors for all of the bends in the optical path. The only prism was the derotation prism in the rotating head.

Having to endure a overly verbose explanation from a non-spatial person of some phenomenon that you can plainly “see” without a long story.2. Tracing unlabeled pipes across floors and walls in an old chemical plant where the knowledgeable staff was no longer available.3. By hand, aligning a tiny solid state diode laser to a single mode optical fiber (~10 microns diameter core). You cannot see the laser’s infrared beam or the fiber’s light transmitting inner core either. With a loupe or microscope at best you can bring the two items to close proximity.You have a light power sensor at the other end of the optical fiber. You fiddle with the stage’s XYZ motion controls until you get some sensor reading (some light in reaching the optical core), then you can very carefully adjust the components’ positions to maximize the power signal. Of course, then you lock the items in place. I used optical cement in my case. which is besides the point. You need a spatial sense to get this done.It is not a physically difficult problem by the way. If somebody shows you a diagram it all seem very simple. It is just that you are working blind and have to visualize objects in three dimensions and how you are moving them for a good while before getting any feedback in terms of a sensor signal.