Subject: HRI/MRI IP TV4 Flash report Date: Sat, 01 Mar 2003 22:35:48 -0500 From: Dennis Wellnitz Hi all, Today (Saturday, March 1) we met at 10 am to plan the day's activities. Because we had found drifts in the bias level dominating the dark current measurements late yesterday, we decided to spend some of the time today tracking the bias level as the preamps and CCDs warmed up after being turned on, to find out how long they required to reach stable bias. Because the day was starting out sunny, but was predicted to become cloudy and snowy, we decided against trying to do MRI flat fields today, leaving that for tomorrow. Instead we decided to do several tests of the MRI and HRI that require neither a good focus nor extremely stable background light. Immediately after the meeting we turned on the CCDs (which were near the automatic heater turn-on temperature of -109 C) and monitored bias every few minutes to see how it changed as the preamps and CCDs warmed up. The bias levels varied from quadrant to quadrant and continued to vary over time, so we decided to continue monitoring the bias occasionally throughout the day, interleaving those tests with the other tests we had planned. Because both the MRI and HRI were still continuing to cool to their operating temperatures, we started with measurements which had little or no dependence on focus, with first emphasis on the MRI. We started with latent image tests of the MRI both in full-frame shuttered mode (which has 5 flushes before each read-out), and in 128x128 shutterless mode (continuous read-out without flushes). In both cases we saw no evidence of a latent image when the CCD had been exposed to a circular image a few tens of pixels in diameter about 100 times brighter than saturation. We then continued with a test of the MRI stimulator, which when on illuminates the side of the shutter facing the CCD. We found a graduated signal across the image ranging from about 700 to 3000 DN for an exposure time of 100 milliseconds, slightly higher or lower for higher or lower supply voltages. This is in the acceptable range, because we can get an adequate, unsaturated signal in every CCD operating mode with a reasonable exposure time. This stimulator will permit us to track local (pixel-to-pixel) variations in responsivity of the CCD to light during the course of pre-flight and in-flight use of the detector. However, because it will vary in brightness in response to the voltage provided to it and may degrade with time and environmental exposure, it will have limitations as an absolute responsivity reference. We then switched over to the HRI and began looking at the IR-FPA, which had cooled sufficiently to come out of saturation. We saw about half of the full-well filled with dark current in the normal mode of operation, so we were able to make some measurements with it. We plan to repeat these measurements when the detector has cooled further. We uncovered the ZnSe window and turned on the SIRTF black body to check the operation of the filter and the baffle that had been installed since the last IR thermal vac tests. With the IR spectrometer we were able to see the long-wavelength illumination from the SIRTF black body as well as the carbon dioxide and water vapor absorptions from the air in the room. When we turned up the black body to high er temperatures that saturated the system response at the long wavelengths (4-5 microns), we saw that the filter was working as expected over the central quarter plus of the slit, and we saw no sign of the shorter-wavelength ghosts we had seen with similar illumination during earlier testing. It appears that the baffle is working well and the filter is doing what we expected. We plan to take more data when the IR detector is colder. We also looked at the Argon spectral lamp with the IR spectrometer to see if just holding it ahead of the ZnSe window would provide enough signal to see spectral lines. We were mildly disappointed that we saw no signal from it under these operating conditions. We will probably try it again when the IR detector is colder, and may also use a concentrator if it isn't too much work to set up and align. Late in the day the MRI had stabilized to a very slow rate of cooling, about one degree C in three hours. So Jim Baer came in and set up a through-focus pinhole test. The results of that test are a bit puzzling, so we need to review and think about them for a while to figure out how to interpret them. We plan to continue with MRI and HRI tests tomorrow (Sunday) starting at 1 pm and continuing until 10 or 11 pm in the evening, because we need to do the radiometry work at night to reduce the influence of ambient light. The cooling will continue overnight and tomorrow. Please let me know if you have any questions or comments. Also please let me know if you would prefer not to be included on this Flash report distribution list, or if there is someone else who should be included on this distribution list. Dennis