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The EEV10 CCD for use on IDS

  1. EEV10: General information on the device
  2. Spectral resolutions. Wavelength coverage
  3. Spatial scale on IDS. Spatial profile degradation at the CCD edges
  4. Fringing and Cosmetic defects
  5. Charge spreading variations. Effects on spectral resolutions
  6. Measured throughput

EEV10: General information

The EEV10 Parameters with UltraDAS + SDSU Gen.3 provides information about physical and operational characteristics of the EEV10 detector as it is currently working in IDS. Data about the detector quantum efficiency, gain, noise, fringing, etc can be found in this page.

Spectral resolutions
Wavelength coverage

The table linked here lists the dispersion provided by each grating when mounted on the 235mm camera. The EEV10 is mounted with its 4096 pixel axis along the wavelength direction, giving maximum use of the beam width leaving the cameras. However the camera optics severely vignette the outer regions of the dispersed light beam such that approximately only 2275 of the CCD pixels are clear and unvignetted. The attenuation runs rises steeply at each end of the spectra. The unvignetted portion is roughly from pixel number 870 to 3145 in the spectral direction. Here is an example plot of a Lamp Flat on the 235mm camera. The points were vignetting starts, and the full free range are marked. The Y-axis is a real measure of the attenuation ratios. 

Spatial scale on IDS
Spatial profile degradation at the CCD edges

The 235mm camera with the EEV10 CCD provides a spatial scale of 0.40 arcsec/pixel. The maximum unvignetted slit-length usable with IDS is 3.3 arcmin, corresponding to some 500 detector pixels for EEV10.

Note that the spatial profile degrades toward the upper and bottom parts of the CCD, giving the impression that in these regions the star image is out-of-focus (most evident in the vignetted regions where a stellar profiles becomes double-peaked). This is a feature due to the IDS optics, in particular the CCD corrector lens, that was not designed for large format detectors like the EEV10 CCD.

Fringing and Cosmetic defects

The thinned chip severely suffers from fringing in the red part of the spectrum, which limits its usefulness in this region despite its good QE up to 8000 Å. Here there is an illustrative flat field spectra (See here the parameters of the detector for more details). The following numbers serve as a reference guide to the severity of the problem :
Wavelength     Peak-to-Peak Amplitude
6500Å                 5%
7000Å                 15%
7500Å                 30%
8000Å                 50%   
8500Å                 60%
9000Å                 60-70%
There are a few cosmetic defects on the surface of the chip, but nothing particularly severe.

Charge spreading variations
Effects on spectral resolutions

The diffusion of charges between pixels during integrations causes a degradation of the spatial and spectral resolution. For a long-slit spectrograph like IDS, with the INT mean seeing around 1".0-1".5, spatial degradation is not a significant with the pixel size of the EEV10, but should be considered in the spectral direction. For a back illuminated CCD this charge diffusion (often referred to as the Modulation Transfer Function; MTF) becomes progressively worse for shorter wavelength incident light. For example, using a slit-width projecting 2 pixels on the detector results in a FWHM measured of 2.4 pixels (measured at ~4000 Å) when the spectrograph is at best focus. Similarly, a slit-width projecting 4 detector pixels will produce a FWHM of ~4.4 pixels (again at ~4000 Å). This effect becomes less severe towards redder wavelengths and is negligible at around 6000 Å. 

Flux standard data and
empirical throughput

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Contact:  (IDS Instrument Specialist)
Last modified: 18 June 2024