Optical instrument for photographing solar spectrum
Solar spectrometerSolar spectrumOptical instruments of[1-2]。Generally, plane diffraction gratings are used as dispersion elements.The focal length of the collimating mirror and imaging mirror is about 10 meters, and the grating line dispersion is generally 5~13 mm/A, or as small as 1 mm/A.Because the solar radiation is very strong, the incident slit can be very narrow, and the spectral resolution is close to the theoretical value of the grating resolution, so it can be used to study the fine structure of the solar spectrum.
The collimating mirror and the imaging mirror are strictly on the same spherical surface;When the distance between the grating and the mirror is equal to 0.84 times of the mirror focal length, the spectral focal plane is a plane.
Littrow system
A self collimating system, the collimating mirror and imaging mirror are the same set of dualAchromatic lensThe difference between the diffraction angle and the incidence angle of the grating is very small, the structure is simple, and the grating is mostly used for vertical spectrograph.
Secondary dispersion spectrograph
Place the middle slit at the focal plane of the imaging mirror for the first imaging to allow only a small segment of the required spectrum to pass through, use the appropriate optical device to return it to the imaging mirror, and then disperse it once again through the grating. The collimator will image and take photos and photoelectric records.The main purpose of using this device is to eliminate most of the scattered light, so as to obtain a high-purity spectrum. At the same time, the linear dispersion can be doubled.
Multiband spectrograph
When placed horizontally, the grating generally does not rotate, and the imaging mirror and negative box of each wave band are arranged along the dispersion direction to simultaneously shoot the solar spectrum of several wave bands.
Instrument manufacturing
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In order to observe the fine structure of the solar spectrum, it is necessary to minimize or even eliminate the adverse effects of the airflow inside the spectrograph on spectral imaging. Therefore, the spectrograph can be evacuated.For the instrument room where multi band spectrograph is placed, thermal insulation and air conditioning measures shall be taken in the building structure to make the indoor temperature uniform with little daily change.In addition, a light barrier is arranged between the collimating mirror and the imaging elements to reduce the scattered light[3]。
