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Copyright © LightForm Inc, 2017
LightForm Inc: Pioneering Analytical Hyperspectral Microscopy Since 1996

A Prism VS Grating Spectrometer Light Throughput and Sensitivity

A Prism Can Offer a 45 X Sensitivity Advantage in the Near IR*

Then bandpass at wavelengths above 800nm = Grating bandpass:  ~2 nm Prism bandpass:  ~10 nm Then net light detection: Grating 10% x 10% x 2 = 2% Prism: 90% x 10% x 10 = 90%
For example, if: Prism efficiency: at 800nm is ~90% Grating efficiency ~10%, at 800nm Detector QE: ~10% at 800nm
* In this example a prism presents a net advantage of 45X when compared to a diffraction grating assuming identical operating parameters.  It should be understood that actual light throughput depends on the NA of the objective, slit width, the actual diffraction efficiency, grating and camera QE... It is fair to say that for non-critical bandpass applications the sensitivity of a prism, over a wide spectral range, will always be greater than that of a diffraction grating.
Grating: The wavelength dispersion is essentially constant across an octave (eg 400 to 800 nm), therefore spectral bandpass increases slowly into the NIR as shown in the figure in the previous page Click here
Net light throughput  = Dispersive element efficiency x QE camera x bandpass at the wavelength in question
Prism: Light is refracted non-linearly through a prism with greater dispersion in the UV and blue than in the red and near IR
LightForm_Logo
Copyright © LightForm Inc, 2017
LightForm Inc: Pioneering Analytical Hyperspectral Microscopy Since 1996
A Prism VS Grating Spectrometer Light Throughput and Sensitivity A Prism Can Offer a 45 X Sensitivity Advantage in the Near IR*
Grating: The wavelength dispersion is essentially constant across an octave (eg 400 to 800 nm), therefore spectral bandpass increases slowly into the NIR as shown in the figure in the previous page Click here
And bandpass at wavelengths >800nm: Grating bandpass = ~2 nm Prism bandpass =      ~10 nm Then net light detection: Grating ~10% x ~10% x ~2 =    2% Prism: ~90% x ~10% x ~10 = 90%
For example, if: Prism efficiency 800nm:     ~90% Grating efficiency ~10%, at 800nm Detector QE: ~10% at 800nm
* In this example a prism presents a net advantage of 45X when compared to a diffraction grating assuming identical operating parameters.  It should be understood that actual light throughput depends on the NA of the objective, slit width, the actual diffraction efficiency, grating and camera QE. It is fair to say that for non-critical bandpass applications the sensitivity of a prism, over a wide spectral range, will always be greater than that of a diffraction grating
Net light throughput  = Dispersive element efficiency x QE camera x bandpass at the wavelength in question
Prism: Light is refracted non-linearly through a prism with greater dispersion in the UV and blue than in the red and near IR