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Unformatted text preview: Diffraction grating spectrometers Diffraction grating spectrometers AGK 2010 Diffraction 123 NASA (JPL) Diffraction grating spectrometers Diffraction grating spectrometers AGK 2010 Diffraction 124 www.jobinyvon.com Resolving power of a grating Resolving power of a grating W h a t do we observe as wavelength shifts ? a b =1 x=f sin m =0 m 1 f f f m x m a AGK 2010 Diffraction 125 Resolving power Resolving power b = 1 , a=75 , N=50 0.8 1 m =1 m =2 m =3 0.4 0.6 0.02 0.03 0.04 0.05 0.2 in Sin ow many discrete wavelengths can be resolved? AGK 2010 Diffraction 126 How many discrete wavelengths can be resolved? What is the smallest wavelength difference that can be resolved? Number of resolvable wavelengths Number of resolvable wavelengths 1 m =1 m =2 4 0.6 0.8 015 02 025 03 0.2 0.4 0.015 0.02 0.025 0.03 2 2 sin sin sin N I I AGK 2010 Diffraction 127 sin / a Number of resolvable wavelengths Number of resolvable wavelengths 1 m =1 m =2 Width of diffraction order (Rayleighs criterion): FSR 4 0.6 0.8 Na 015 02 025 03 0.2 0.4 Diffraction order spacing: 0.015 0.02 0.025 0.03 2 m m a 2 sin sin sin N I I 1 m m a a AGK 2010 Diffraction 128 sin / a a Number of resolvable wavelengths ctd Number of resolvable wavelengths ctd 1 m =1 m =2 4 0.6 0.8 015 02 025 03 0.2 0.4 Na 0.015 0.02 0.025 0.03 a AGK 2010 Diffraction 129 Number of resolvable wavelengths ctd Number of resolvable wavelengths ctd Number of resolvable peaks between orders m and m +1: 1 m =2 m =1 4 0.6 0.8 N N 015 02 025 03 0.2 0.4 Na I.e. number of resolvable wavelengths is just a function of the number of periods in 0.015 0.02 0.025 0.03 a the grating AGK 2010 Diffraction 130 Resolving power Resolving power 0.8 1 0.4 0.6 0.015 0.02 0.025 0.03 0.2 Na Resolving power is defined as the ratio of the centre wavelength to the smallest resolvable wavelength AGK 2010 Diffraction 131 difference Resolving power Resolving power 0.8 1 m m + 1 Just resolvable difference when: 0.4 0.6 ' m m m m 0.015 0.02 0.025 0.03 0.2 a a N a m N Na...
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This note was uploaded on 09/28/2010 for the course ECSE ECSE 527 taught by Professor Kirk during the Winter '10 term at McGill.
 Winter '10
 Kirk

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