Nickel mesh for Extreme UltraViolet Imager
Extreme UltraViolet Imaging Telescope is a device that is used on spacecraft to collect the high resolution images of solar corona.
Extreme ultraviolet rays enters the telescope by a thin metal film filter that suppresses the most of the UV, visible and IR radiation and keeps the solar heat away from the telescope. The radiation travels through the quadrant selector to the optics quadrants that consist of primary and seconadary mirror made to handle the EUV lines.
After reflected by primary and secondary mirror, the radiation travels through the filter wheel that comprises of thin-layer aluminium filters to prevent the remaining while light and IR rays. A moving blade shutter manages the exposure period. An image is made on a CCD detector.
Filters
The thin metal film filters at the entrance aperture and close to the focal plane at EUVI
suppress the unwanted UV, white light and infrared radiation. There are two filters at the entry point of telescope- aluminium on-polymide foil on a nickel grid and one aluminium foil on a fine nickel mesh, these filters prevent the entrance of visible light. The polymide layer on the nickel grid allows the filter support by grid with nominal distance that causes little diffraction at ultraviolent wavelengths.
The polymide only sends around 50% of EUV radiation at the observing wavelength however this is not a crucial factor for powerful lines of higher width. The nickel mesh supported filter prevents the absorbing polymide layer that offers nominal transmission at longer wavelengths, particularly for a weaker line.
Although the fine mesh having 0.36mm line spacing, results into significant diffraction. Both kinds of filters flow on a successful tests: the telescope used a plastic strengthened aluminium foil on an almost identical coarse grid for the whole wavelengths and Trace utilized fine mesh filters similar to those used on EUVI. Aluminum mesh filters on a fine mesh are caped in a filter steel. This wheel provides frequent filters if he development of pinholes is needed on orbit. Another filter wheel position comprises of double filters in series to alleviate against the catastrophic damage to the entrance filters. 4th filter slot is kept open, basically for ground testing.
The nickel wire mesh used in these filters is fabricated by Heanjia Super-Metals.
Use of EIT equipment
EIT is the first device that employs general incidence multilayer coated optics to create the image of the sun in the extreme UV rays. This part of the spectrum is hardly bounced back because most of the matter soaks the light completely. Traditionally, these wavelengths are reflected by using grazing incidence or a diffraction grating. Advanced vacuum based techniques uses mirrors that are coated with fine layers of any material.
The multilayer technology enables the use of traditional telescope forms in the spectrum. Images of sun with multilayer optics, are used in terrestrial nanolithography rigs for the development of microchips. Aluminum filter with nickel wire mesh is used to prevent the entrance of visible light while allowing EUV radiation.
