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SLIT - Fibre-optic fed slit-spectrograph


Instrument P.I.: Michael Winter, University of Stuttgart, Germany.


The information below will be updated as more precise data is received.

Technique: A high-resolution slit-spectrgraph which is fed by optical fiber attached to window assembly telescope.

Scientific objective: Resolve shock emissions in the near-UV.

SLIT Instrument: The instrument consists of a computer controlled slit-spectrograph which is fed by an optical fiber and a small telescope assembly at the window. A co-aligned camera provides pointing capability, detecting stars to magnitude +7. The camera is an EM CCD Andor DU97 IN, back illuminated UV enhanced CCD, with 1600x400 pixels (16x16 micron) and 25.6 x 6.4 mm image area. The Spectrometer is an Acton Sp300i imaging spectrometer with 300 mm focal length F/D 4.5. The telescope assembly focussing is performed with a 90 degree off-axis parabolic mirror of 50 mm diameter with a focal length of 100mm. The F/D~2 was chosen to meet the numerical aperture of the fibre optics yielding an angle of view of 0.45 degree. A bundle of 50 quartz fibres of 100 Ám diameter are chosen. On the telescope side the fibres form a round cross section of 0.8 mm diameter, on the spectrometer side they are oriented in a row which can be used like a slit with a height of 5.6 mm and a width of 100 micron. If sufficient amounts of light are available, a slit can be used in addition to improve the spectral resolution.

Heritage: The same telescope assembly was deployed during the 2002 Leonid MAC mission, feeding a rack-mounted slit-spectrograph.

Aircraft hardware requirements: Window swivel mount. Stow box. Rack mounted spectrometer and computer.

Instrument validation tests:

Sensitivity: The Electron multiplier gain is 1 - 1000 times, the pixel read out rate 0.05, 1, and 3 MHz.

Dynamic range:

Frame rate and exposure times: Maximum rate of spectra per second in full vertical binning mode: 328 up to 400 per second.

Spectral resolution - gives the FWHM of an instrument-broadened unresolved atomic spectral line:
A choice of spectral resolutions between 0.17 and 2.0 nm is available. Gratings of 50, 150, 300, 600, 1200, 1800, or 3600 l/mm are available, providing the following choice in resolution and wavelength coverage:

grating       wavelength      range   pixel resolution   FWHM       FWHM
  lines/mm        nm          nm             nm          Slit+F0     F0
   300            300         490            0.3         0.7         2
   600            300         245            0.15        0.4         1
   1200           Hol.        120            0.077       0.2         0.5
   1800           500         80             0.05        0.12        0.33
   3600           hol.-UV     40             0.025       0.07        0.17   

Relative spectral response - gives the wavelength dependence of the combined system (window, lens, spectrograph, and CCD camera) for each of the gratings given above:

spectral response curve

wavelength:  Quantum Efficiency: 
   (nm)     (percentage) 
            1200 l/mm   300 l/mm   600 l/mm   1800 l/mm   3600 l/mm 
200         72.0         31.3      80.0         
225         85.3         
250         78.7         60.0      
300         61.3         75.7      60.0         20.9          48.0
350         50.7                                39.1          52.5
400         40.0         60.0      47.5         54.8          49.3
450         32.0                                57.4          45.1
500         24.0         44.3      37.5         75.7          41.4
550         21.3                                65.2
600         20.0         30.0      27.8         58.7
700                      22.2      20.0      
800                      17.0
900                      14.3