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INTRAPIX

The INTRAPIX project: study and realization of a characterization bench of the intra-pixel visible and infrared detector respond for spatial astrophysics

 

CONTEXT:

The response variation of a sensor at sub-pixel level is generally considered as a second order effect in the measurement error budget. Therefore, it is currently not specified in the projects, thus not measuring by producers and/or sensors users.
Nevertheless, a response variation can contribute to the global error budget, for example in the case of a sub-sampled instrument. It can be true for ones dedicated to precise measurements of shape or photometry (for example, the two instruments in the visible and infrared of the EUCLID spatial mission). Another case is met during the successive observation of a same object, for example the exo-planet transit around its star, where it is necessary to repoint a telescope in the same field with enough precision.

The acknowledgment of the intra-pixel response variation of the SPITZER-IRAC camera’s sensor allowed the acquisition of a proper light curve. It follows the correction of the scientific data from the signal fluctuations induced by the temperature variation of the instrument’s optical bench and thus, the displacement of the source against the sensor. Finally, in the case of a wide field instrument dedicated to wide records in the sky, the important parameter is the homogeneity of data all along the measurement. It is especially crucial to know the image quality variation in all the field of view, and thus not only the mean profile of the intra-pixel response but also the variation of this response in the sensor’s surface. All these reasons lead the European Spatial Agency, for example, to ask intra-pixel responses measurements since the R&D earlier phases of the development of new sensors.

Such a platform can be used for a wide variety of applications: the characterization of the VIS instrument visible sensor from the EUCLID mission, the characterization of the METIS instrument sensors from the future E-ELT telescope, the ground support of the MIRI instrument from the JWST spatial telescope, the characterization of the sensors from the EChO mission,…

 

THE PROJECT:

The project constists on the realization of a characterization bench of the intra-pixel response variation of space and terrestrial detectors with large focal planes for the visible and infrared (near and mid-infrared). This bench will be part of the detector characterization platform for Irfu astrophysics and will therefore be available to other member laboratories of the GIS MOTESPACE. This bench will allow the fine characterization of the entire surface of a detector and in this sense will be unique in France and in the world.

The proposed bench aims at characterizing detectors over a wide range of wavelengths, from the visible to the thermal infrared. The projects concerned are Euclid-VIS, JWST-MIRI, ECHO, E-ELT-METIS, R&D NIR and LWIR of CEA-LETI. This bench will be designed (cryogenics, vacuum, optics...) to be usable also in the thermal infrared, the passage to other wavelengths and other detectors being obtained by changing the source and the test pattern. The scientific specifications considered for the design phase of the bench are to measure the spatial response of the detectors to:

  • monochromatic wavelengths:
    • VIS : 550, 750, 900 nm
    • NIR : 1030, 1260, 1500 nm
  • polychromatic bands:
    • VIS : R, I, Z (550-900 nm)
    • NIR : Y, J, H (1.0-1.6µm)
    • LWIR : 7-11µm
  • with a measurement resolution of 1/12 pixel for VIS and NIR, and 1/10 to 1/8 for LWIR

At this level of resolution, specific test patterns were dimensioned and simulated. In addition, it has been demonstrated that a new measurement methodology is needed, which consists in finely moving the test pattern in front of the detector in order to reconstitute a super-resolved image and then processing this "super-image" to trace back to the intrapixel profiles.

 

THE CHARACTERIZATION BENCH:

The bench consists of a point source placed at the focal point of a collimator (Figure 1). This device makes it possible to obtain a polychromatic plane wave arriving under normal incidence on the periodic test pattern (CSIG). The test pattern is placed in front of the detector to be characterized housed in a dedicated cryostat. It is fixed to a displacement plate with a resolution of the order of a micron to ensure its displacement in X-Y in the detector field.

Fig2.png

 

 

#189 - Last update : 25/01/2021

 

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