7/26/2023 0 Comments Spectrometer grating dispersio![]() In ruled and ruled holographic gratings, changing the groove angle (the angle created by the longer side of the groove and the plane of the grating) moves the diffracted radiation along the spectral region and changes the blaze wavelength. The overall shape of the grating efficiency curve (a plot of absolute or relative diffracted efficiency as a function of the diffracted wavelength) shows normally a single maximum, at the peak of maximum brightness (or blaze wavelength) and is generally a rather complex function of wavelength and polarization of the incident radiation and depends on the groove density, plane of polarization, shape, and angle of the grooves and the reflectance of the coating material. Grating EfficiencyĪs grating diffracts the incident radiation, it does not do so with uniform efficiency. Increasing the groove density leads to a higher optical resolution but also to a shorter wavelength operational range (see Figure 1).įigure 1 – Absolute efficiency curve of 3 gratings with 1800 (orange), 2400 (blue) and 3600 (black) grooves/mm. On the other hand, groove density also defines the operational range of wavelengths of the grating, being that a higher groove density will generate shorter operational ranges for your spectrometer. The increase of the groove density (grooves (or lines)/mm) results in an improvement of the optical resolution for a certain slit width. ![]() The groove density or groove frequency is usually expressed in nm/mm and determines the range of wavelengths that are dispersed by the grating into the detector. ![]() Detailed information about these two parameters can be found in the following sections. The two key parameters when choosing the right grating for your spectrometer are the groove density which allows you to set the operational wavelength range and optical resolution and the grating groove efficiency for the selection of the wavelength range where your system sensitivity is at its maximum. What are the key parameters when choosing the right grating for your spectrometer?Īll spectrometers manufactured by Sarspec are equipped with fixed diffraction gratings that can be selected by the user according to the wavelength range of interest. ( b) The camera with the 2D BSI-CCD array detector was placed on top of the grating module with a small off-axis tilt of approximately 6° in the direction perpendicular to the diffraction plane without the coma effect. F is the set of filters applied to cut off the high order ( m ≥ 2) of the diffracted light effectively in each sub-spectral range. The grating-diffracted light along path 元 is then focused at the 2D focal plane of the CCD detector along path L4 after reflected by toroidal mirror M2 with an off-axis angle of β = 0. The light along path L2 becomes parallel after reflected by spherical mirror M1 and then enters module Gx with an off-axis angle of α = 0. The incident light enters along path L1 through a hole centered between gratings 22 and 23. S indicates a light beam slit, and Gx is the integrated module composed by 44 sub-gratings. ![]() Schematic illustration of the high-resolution coma-free spectrometer. ![]()
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