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The RED+2 CCD for use on IDS

  1. Red+2: General information
  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
  7. IDS Red+2 Commissioning Report

RED+2: General information

The RED+2 Parameters with UltraDAS + SDSU Gen.3 provides information about physical and operational characteristics of the Red+2 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 RED+2 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 2200 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 800 to 3000 in the spectral direction. Here is an example plot of a lamp flat on the 235mm camera with RED+2 CCD.  

Spatial scale on IDS
Spatial profile degradation at the CCD edges

The 235mm camera with RED+2 CCD provides a spatial scale of 0.44 arcsec/pixel. The maximum unvignetted slit-length usable with IDS is 3.3 arcmin, corresponding to some 450 detector pixels for RED+2.

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 RED+2 CCD.

Fringing and Cosmetic defects

RED+2 chip suffers from mild fringing. Here there is an image of a flat field spectra showing fringing in the redmost part (from around 9000 Å) and here there is an example showing the fringing modulation along the whole RED+2 CCD with R300V grating covering up to 10000 Å. In this image, for comparison the fringing modulation of the EEV10 detector was included. The level of fringing for the RED+2 detector is less than 2% in all interval, with an average of about 1%.

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 degrading 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 significant with the pixel size of the RED+2, 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 (at ~4000 Å). This effect becomes less severe towards redder wavelengths and is negligible at around 6000 Å.

Measured throughput

IDS Red+2 Commissioning Report

IDS Red+2 was commissioned in 2011. All the technical information regarding the detector commissioning can be found in the "IDS REDPLUS2 Commissioning Report" by O. Vaduvescu and A. Riddings.

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