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The Fourier relationship between input frequencies and output interferograms is demonstrated and a practical demonstration in analysing gases is examined.
Metadata describing this Open University video programme
Module code and title: ST291, Images and information
Item code: ST291; 05
First transmission date: 28-04-1977
Published: 1977
Rights Statement:
Restrictions on use:
Duration: 00:22:31
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Producer: Andrew Millington
Contributors: Barrie Jones; Alan Walton
Publisher: BBC Open University
Keyword(s): Car exhausts; Carbon monoxide; Cosinusoid; Interference pattern; Interferogram
Footage description: Shots of a laser double slit interference pattern. Barrie Jones introduces the programme with a brief explanation of the principles of the Michelson interferometer. Jones uses a diagram to illustrate his points. Alan Walton in the studio with a basic Michelson interferometer set up. He points out the main components and explains how the apparatus works. Walton then demonstrates the instrument using a collimated beam from a mercury discharge lamp to obtain constructive and destructive interference pattern. Barrie Jones explains why the spectrum of the source is important in working back from an interferogram to gain information on the nature of the source. Alan Walton sets up the Michelson interferometer to obtain an interferogram for a single frequency spectrum. Walton points out the various components of the apparatus and then runs the experiment. Shots of a pen recorder tracing out an interferogram for this spectrum Barrie Jones and Alan Walton next consider a spectrum which has been broadened to include a whole band of frequencies. Shots of an interferogram being run on the apparatus. Walton then broadens the spectrum even further and examines the resulting interferogram. Barrie Jones, with the aid of animated diagram brings out the relationship between spectral bandwidth, coherence length and coherence time. He then points out that as a result one can, by Fourier transformation, obtain a spectrum from the interferogram. Film shots of Alan Walton taking a sample of the exhaust gases from a car parked outside the Warren Spring Laboratories at Stevenage. He holds the sample up to the car's reversing lights to demonstrate that not much light is absorbed in the ordinary visible region of the spectrum. Walton, inside Warren Spring Laboratories, examines a Michelson interferometer of the type used there for the analysis of car exhaust fumes. The technique used is Fourier transform spectrometry. Walton points out the component parts of the apparfus and explains the function of each. Walton next examines the results of a typical run. The data is displayed on an oscilloscope, then with a pen recorder and finally, in order to present a clearer picture, the ratios are displayed on the oscilloscope. Barrie Jones, with the aid of diagrams, compares the Michelson interferometer with the double slit as a means of investigating spectra. He points out the advantages of the Michelson method.
Master spool number: HOU2354
Production number: 00525_1245
Videofinder number: 2116
Available to public: no