University of St Andrews
School of Physics and Astronomy
13. Multiple-beam interference
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Associated tutorial questions (St Andrews only)
- We extend the ideas of two-beam interference to three-beam, six-beam and N-beam interference
- Using phasor diagrams we see that multiple beam interference effects give much sharper primary maxima than do two-beam interference
- We will look at one of the main applications of multiple beam interference, its use in the "Diffraction Grating" mulitple-beam interference device for separating light of different wavelengths for spectroscopy
- The more beams that interfere in multiple slit interference patterns, the more chance there is of separating spatially light of two similar wavelengths
- Other areas of use include the Fabry Perot Interferometer (JH labs), which is used for separating light of closely spaced wavelengths using multiple-reflections between two mirrors
- Nature got there first; the irridescent colours seen in some butterflies and birds are due to multiple reflections of light from periodically structured scales or feathers
- But technology is catching up - multiple and constructively interfering small reflections can lead to a multi-layer dielectric mirror used in conventional lasers or, using semiconducotr layers the mirror in a "Vertical Cavity Surface Emitting Laser". The same ideas of creating patterns on a wavelength scale in semiconducting materials can give rise to multiple reflections and new guiding mechanisms for light. Our Thomas Krauss is a leader in the field of semiconductor microstructures, and Bath's optoelectronics group are world renowned for their work in "holey" optical fibres.
Similar material to that presented in the lectures is available at:-
- Halliday, Resnick, & Walker - Chapters on:- Interference, Diffraction
Associated tutorial questions (St Andrews only)
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Created by, and copyright of, Bruce Sinclair, University of St Andrews; last modified 11/09/01