Re: What would you see between two parallel mirrors?

Area: Physics
Posted By: Adrian Popa, Staff Optical/Microwave Physics
Date: Wed Oct 8 15:03:05 1997
Area of science: Physics
ID: 876162495.Ph

Message:

Greetings:

The device you are describing in your question has been used in optical physics for more that a century and is called a Fabry-Perot (FP) interferometer, FP resonator or FP cavity. The ruby crystal in the world's first laser was formed into a FP resonator by coating the ends of the ruby laser rod with mirrors. For the laser to work the end mirrors must be very parallel.

If you hold a flat hand mirror toward a wall mirror you will see a tunnel of mirrors in the reflection that appears to go on to infinity. However, each reflection of the mirror appears smaller and farther away as the light beam bouncing back and forth traveling greater and greater distances. If you use high quality mirrors in this experiment you will not be able to look down the center of the tunnel from the edge of the mirror; however, if you put a small hole in the center of the hand held mirror and look through it, you can perfectly align the tunnel of mirrors. This is how the first laser was constructed. If you read my answer to the question How do lasers work? in the Mad Scientist archives you can see a picture and learn more about the first laser and it's Fabry-Perot resonator.

Other : Re: CAN I HAVE INFO. ON LASERS, PLEASE?CAN U SEND INFO THAT I WILL 
UNDERSTAND? 
Adrian Popa, Staff Optical/Microwave Physics, Wed Mar 5 11:48:13 1997

Eac time the light beam passes between the mirrors of a laser, it is amplified and gets more intense with about 1% of the output power coming out of the small hole in the mirror center for us to use. Because laser light is coherent (a single wavelength or color) the light produces interference effects within the Fabry-Perot resonator. This interference causes a number of interesting patterns of light structure in the resonator called modes. A more complete discussion of Fabry-Perot resonators with pictures of the various modes can be found at the following Web pages:

http://www.achilles.net/~jtalbot/glossary/fp.html

If you are interested in simulating interference on a PC I have written a program in BASIC to answer a question about interference in the Mad Science archives at the following location:

Physics : Re: When waves collide, do both kinds of interference occur? 
Adrian Popa, Staff Optical/Microwave Physics, Tue Jan 21 11:42:59 1997

Your Mad Scientist "Through the Looking Glass"

Adrian Popa "Imagineer"

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