A multichannel high-resolution spectrometer is a spectrometer-polychromator that enables simultaneous high spectral resolution and operation across multiple spectral ranges. The presented spectrometer-polychromator allows operation in three spectral ranges. The spectrometer-polychromator is based on transmission holographic volume-phase diffraction gratings and is designed for operation in the visible and near-infrared spectral ranges. The high-resolution spectrometer-polychromator is so-called high-etendue spectrometer (HES). Furthermore, HES features a large optical aperture, with a F-number ranging from 1/3 to 1/2.2. This, combined with the high linear dispersion of HES, facilitates spectroscopic measurements with a high etendue.
The figure below shows the HES optical scheme.
Optical scheme of the three-channel spectrometer. 1 – entrance slit; 2 – entrance objective lens; 3 – transmission diffraction gratings; 4 – exit objective lenses; 5 – light trap; 6 – instrument housing; 7 – image planes.
The spectrometer-polychromator is equipped with sequentially arranged one after the other transmission diffraction gratings. The following requirements are imposed in diffraction gratings with this HES scheme: the gratings must have high diffraction efficiency within their operational spectral range and high transmission in the remainder of the visible range. The first grating has a high diffraction efficiency for the wavelength range of 468 ± 5 nm, and high transmission for other lengths pass through the transmission grating. The second grating has a high diffraction efficiency for the wavelength range of 529 ± 5 nm, and high transmission for other lengths passes through the transmission grating. The third grating has a high diffraction efficiency for the wavelength range of 656 ± 6 nm, and high transmission for other lengths also passes through the transmission grating.
The main technical data of HES [1]:
· Operating spectral ranges: 468 ± 5 nm, 529 ± 5 nm and 656 ± 6 nm;
· Diffraction efficiency of gratings: 40-50%;
· F-number: 1/3; 1/2.2;
· Inverse linear dispersion: 3.4 - 5 Å/mm (up to 7 Å/mm)*;
· Astigmatism value: ~ 0.025 mm;
· Optical reduction ratio in both planes: ~ 1 (~ 1.5)*;
· Entrance slit height: ~ 20 mm;
· Image plane size: up to 20×25 mm;
· Max. spectral resolution ~ 0.2 Å;
· Contrast: K > 770 000.
*Parameters with short-focus exit objective lenses.
The three-channel spectrometer-polychromator described above was originally designed for Charge eXchange Recombination Spectroscopy (CXRS) in high-temperature plasma research facilities. However, HES can be adapted for various spectroscopic applications that necessitate the measurement of spectral line profiles or fine spectral structures. In such instances, it is possible to select alternative operational spectral ranges, as well as to determine the width of the wavelength range and the number of spectral ranges employed. The spectrometer-polychromator can be used for spectroscopic measurements requiring high contrast for different spectral ranges.
Registration systems are tailored through individual negotiations, depending on the specific tasks and requirements of the customer. Currently, HES is offered in three distinct versions, corresponding to the aforementioned operating spectral ranges. The key technical parameters for the three HES options are presented in the table below.
|
Entrance F-number |
Optical reduction ratio |
Inverse linear dispersion [Å/mm] |
Spectral range in channels [Å] for two options of camera detector length | ||
| 13,3 мм | 22,5 мм | ||||
| 1 | 3 | 1 | 3.6 3.9 5.0 |
48 52 68 |
81 88 114 |
| 2 | 3 | 1.5 | 4.9 5.3 6.8 |
66 71 91 |
110 120 150 |
| 3 | 2.2 | 1 | 4.9 5.3 6.8 |
66 71 91 |
110 120 150 |
Examples of spectral profiles obtained by HES.
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The spectral profile of a hydrogen-deuterium lamp and a neon lamp in the HES red channel.. |
The spectral profile of a neon lamp in the HES green channel.
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Photo of the HES. 1 – entrance slit; 2 – entrance objective lens; 3 – transmission diffraction gratings; 4 – exit objective lenses; 5 – light trap; 6 – instrument housing.
REFERENCES
[1] Kuz’min, N.V., Tugarinov, S.N., Serov, V.V. et al. High-Etendue High-Resolution Spectrometer−Polychromator Equipped with Novel sCMOS Cameras for Tokamak Plasma Spectroscopy. Instrum Exp Tech 66, 971–982 (2023).