# Interesting Optics Measurements?

by hy23
Tags: interesting, measurements, optics
 P: 64 So I'm really interested in the field of wave optics, and luckily for my undergraduate program, we get to do a measurement project on any area of our choosing. I was looking up topics and there are some interesting ones such as the luminous fountain where they use the idea of fiber optics to illuminate a stream of water. I'm sort of thinking about incorporating some interference of magnetic fields or sound waves, perhaps even duplicating an apparatus such as the Michelson interferometer. But right now all I have is just a jumble of ideas and no direction. I need to actually perform an experiment that will give me quantitative results that can be statistically analyzed and then interpreted for any practical implications. Any ideas for possible measurements I can make?
 Sci Advisor P: 2,417 Microwave interferometer is a fairly good hands-on experiment you can do, provided you can find a safe microwave source and a descent detector. For the source, one usually uses a magnetron from microwave, but set to a much lower power level. For a detector, they have some microwave leak detectors you could buy. Your university might have either or both of these things already set up. Anyways, from there, you just set up a Michelson interferometer, but using wire meshes for mirrors. A mesh with cell size comparable to the wavelength would let a portion of radiation through and reflect the rest, working like a splitter mirror in optical interferometer. A mesh with much smaller mesh size would work as an ordinary mirror. The upshot here is that you are dealing with wavelengths that are about a decimeter rather than half a micron. This means that "mirror" positioning can be done entirely by hand, instead of having to rely on precise micrometers.
P: 5,403
 Quote by hy23 So I'm really interested in the field of wave optics, and luckily for my undergraduate program, we get to do a measurement project on any area of our choosing. I was looking up topics and there are some interesting ones such as the luminous fountain where they use the idea of fiber optics to illuminate a stream of water. I'm sort of thinking about incorporating some interference of magnetic fields or sound waves, perhaps even duplicating an apparatus such as the Michelson interferometer. But right now all I have is just a jumble of ideas and no direction. I need to actually perform an experiment that will give me quantitative results that can be statistically analyzed and then interpreted for any practical implications. Any ideas for possible measurements I can make?
I've seen a great project measuring the track spacings on CDs and DVDs using diffraction. More ambitious would be setting up an interferometer to measure the thickness of a thin film- for example, the shape of a drop of fluid.

It depends on the type of instrumentation you have access to, and your level of expertise in constructing optical instruments.

P: 64

## Interesting Optics Measurements?

nice ideas guys, well I have finally decided on my idea, what I'm not sure about is if it's doable

So here it is: I want to investigate sound waves by utilizing an apparatus similar to the Michelson interferometer and analyzing the diffraction pattern. So I will have a tank of water with underwater speakers producing sound waves in the tank. I will then have a laser outside the tank directed towards the tank, the laser light will encounter a beam splitter before reaching the tank, one beam goes thru the tank (and interfere with sound waves) the other beam goes around the tank (reflected around by mirrors), the two beams rejoin on the other side of the tank and interfere and hits a screen and produces some sort of pattern. I'm hoping that by interpreting this pattern, it will tell me something about the sound wave that caused any disturbance in the first beam.

Is this reasonable? Please feel free to criticize.
 Sci Advisor P: 5,403 Sounds somewhat reasonable- very similar to solid state acousto-optical devices. Those work with ultrasound frequencies and standing waves, so it may be helpful to do some analysis before construction begins, or you may not see anything. Edit- just to make sure, you said "similar to the Michelson interferometer and analyzing the diffraction pattern."- do you mean analyzing the *interference* pattern? Or do you want to construct an acousto-optic deflector- those diffract the beam?
 P: 64 yes not seeing anything is what I'm worried about, cause I'm not sure if any interference that sound may have on the light can actually be detected without the aid of expensive stuff, I also don't know much about interference and optics (actually I don't know much about anything haha ) but I like a challenge and I guess i meant the interference pattern cause there wouldn't be a diffraction pattern in what I have just described btw I looked up solid state acousto optical devices, looks like complicated stuff, how do they work?
 Sci Advisor P: 5,403 Pretty much like how you described your water tank: For deflectors, standing (sound) waves are set up in a crystal (usually Tellurium dioxide or Lithium Niobate), which, due to the spatial variation in density creates a spatially varying refractive index. This then acts as a diffraction grating. I've used devices made by IntraAaction: http://www.intraaction.com/index.html

 Related Discussions Atomic, Solid State, Comp. Physics 3 Classical Physics 1 General Physics 6 General Physics 6 Introductory Physics Homework 12