Second And Higher Order Diffraction | Second and higher Orders Diffraction Pollutes First Order

Spectrum showing second order contamination

Spectrum though a prism shows a total absense of second order

Understanding Second and Higher Order Diffraction A First Order Spectrum Will Repeat In Second Order In Diffraction Grating Based Spectrometers Here a diffraction grating diffracts light emitted by an MIDL lamp. Spectral features appear in first order between 400 nm and 500nm and reappear in second order between 800 and 1000 nm. Spectral detectors are always located in first order, therefore, second order contaminates first order and must be filtered out. Second and higher orders bleed light away from the spectral detector enough that in this example first order efficiency at 436 nm is reduced by about 50% due to second order diffraction. To learn more about gratings and spectrometers visit “Resources” Diffraction Grating Prism In this prism based system there can be no

higher orders because there is refraction not

diffraction. Therefore, there is no contamination of the spectrum between 800 and 1000 nm. All available light, at all wavelengths, is sent to the detector to deliver the highest possible light throughput

Spectrum showing the effect of second order on efficiency

150 g/mm diffraction grating: In this example there are 25 orders 300 g/mm diffraction grating: In this example there are13 orders. 600 g/mm diffraction grating: In this example there are 7 orders $Link to diffraction order movie$

Play to see real how grating orders present themselves Each ray that is diffracted into higher orders is light lost to the detector The first order spectral detector goes here Light lost to Second Order Contamination LightForm Inc: PARISS® Analytical Spectral and Hyperspectral Imaging Each “ray” is a diffracted order that bleeds light from first order. Each “ray” is a diffracted order that bleeds light from first order.