Infrared focal plane arrays are widely used for astronomical observations and are constantly optimized to provide higher-quality images. The knowledge of the pixel spatial response becomes critical to extract ever more data from scientific missions. A specific cryogenic spot scan objective with an f-number of 1.2 has been developed in order to finely characterize 15 μm (or smaller) pixel pitch cooled infrared focal plane arrays in the spectral band between 3-5 μm. It will be operated in the MIRCOS test bench with different narrow-band filters. We present the first optical characterization of this objective obtained with a cryogenic wavefront analyzer – a quadrilateral shearing interferometer. The measured wavefront indicates a peak-to-valley amplitude of 2 μm, which corresponds to an optical quality of about λ/2 at 3.75 μm working wavelength. This value higher than expected might be due to a non-uniform cooling of the objective.
Absolute Quantum Efficiency (QE) measurements are very demanding. To measure the QE of detectors from 0.8μm to 12.5μm a dedicated test bench has been built. The Quantix test bench relies on an optical design ensuring a uniform flat-field illumination of the detector. The illumination uniformity was measured with photodiodes built and calibrated at CEA/LETI. While performing QE measurements, the calibrated photodiode is placed in the vicinity of the detector to measure the incident flux. The Quantix test bench has been validated with a detector whose QE has been measured at the European Space Agency. In this paper, the test bench will be described in details and QE measurements performed on near infrared, MCT-based detectors will be presented. The intra-pixel response is also an important parameter to know as it can affect the accuracy of photometric and shape measurements. The Intrapix test bench has been specifically designed for this measurement, using the Talbot effect to simultaneously measure the intra-pixel response in a large number of subareas of a given detector, from 0.5 μm to 12 μm. The paper will give a brief status of the test bench development.
Type-II InAs/GaSb superlattice (T2SL) has recently matured into a commercially available technology addressing both MWIR and LWIR spectral domains. As the prerequisites such as Quantum Efficiency (QE) and dark current were met, more advanced figures of merits related to the ElectroOptic (EO) system as a whole can now be studied in order to position this technology. In this paper, we focus on modulation transfer function (MTF) measurements. Knowing the MTF of a detector is indeed of primary importance for the EO system designers, since spatial filtering affects the system range. We realized MTF measurements on a 320x256 MWIR T2SL FPA provided by IRnova, using a Continuously Self Imaging Grating (CSIG). The advantage of this experimental configuration is that no high performance projection optics is required. Indeed, the CSIG exploits the self-imaging property (known as Talbot effect) to project a pattern with known spatial frequencies on the photodetector. Such MTF measurements have never been done in Integrated Detector Dewar Cooler Assembly (IDDCA) configuration, so we had to study the effect of the vibrations induced by the cryocooler. Vibrations indeed affect the MTF measurement in the same way electrical diffusion would do. Using three accelerometers we optimized our experimental setup and extracted MTF measurements with reduced vibrations. The pixel size is 26μm for a pitch of 30μm.
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