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M74050
1/4M IMAGING SPECTROGRAPHS
26
7 SPECTROGRAPH RESOLUTION AND BANDPASS
Gratings are available in various groove densities (i.e. lines/mm). Higher groove densities have higher
reciprocal dispersion and therefore higher resolution. The spectrograph bandpass with a 1200 lines/mm
grating is half that of the same arrangement with a 600 lines/mm grating. Note that this simple relationship
is not accurate for slit widths below 50 µm, as the optical aberrations begin to play a role in the bandpass
and resolution.
Using a grating with a high groove density may increase resolution, but the spectral range narrows. The
dispersion of a grating changes inversely with the groove density. If the groove density is halved, the
dispersion is doubled. A spectrograph mechanism can only tilt the grating through a limited range of angles.
The angle and groove density determine the transmitted wavelength.
The gratings can be tilted to 0 degrees, so the lowest possible wavelength for a UV grating is set by the
transmittance of air at about 180 nm. The ability to output wavelengths below 180 nm is also dependent
on the efficiency characteristics of the grating.
The following graphs are intended to illustrate the effects of slit width selection, in terms of throughput and
resolution. The concept of resolution is easily visualized by using the output of a monochromator, which is
also the type of output achievable by the MS260i lateral port (dual output port instruments only) This data
was taken using Oriel’s CS130 monochromator and using various slit widths to change the resolution. The
concept of resolution vs. slit width is the same for the MS260i spectrographs.
Figure 18: Resolution vs. Throughput
Содержание Oriel MS260i Series
Страница 23: ...M74050 1 4M IMAGING SPECTROGRAPHS 23 Figure 16 Grating Efficiency Curves High Resolution and Holographic Models...
Страница 33: ...M74050 1 4M IMAGING SPECTROGRAPHS 33 Figure 244 Model USFW 100 Filter Wheel...
Страница 46: ...M74050 1 4M IMAGING SPECTROGRAPHS 46 14 DIMENSIONS Figure 33 MS260i Dimensions...