Ay 105 Lab Experiment #8: Infrared Array CameraPurposeIn this week’s lab, you will study the characteristics of an InSb near-infrared to thermal-infrared array camera, take pictures, set up an infrared spectro-graph and examine features in a near-infrared spectrum. The camera is sensitive from∼ 2− 4µm. In the first part, you will acquire images of various infrared sources, includ-ing a cooling cup of water, and analyze them on the computer. In the second part, youwill image the spectrum of a hot wire seen through the atmosphere in a lab, using asimple grating spectrograph. As there is a single camera, both groups can acquire thefirst set of images together. Then, while one group is analyzing the first set of images,the other group can obtain the wire spectrum images.Pre-Lab• What is significant about the temperatures 310 K and 77 K?• What is the ratio of radiant energy at 2.5 microns between a 310 K and 77 Kblackbody? How about at 4.5 microns?• Review your work in previous labs:- planck function (Expt 1)- spectrographs and the grating equation (Expt 3)- infrared detector (Expt 7)EquipmentIRC-160 camera d ewarliquid nitrogenvented funnelmirrorplexiglass2 coffee cups with water, one heatedthermometerlightbulb and postcollimating mirrortranslational stagediffraction gratingrotational stagepc and image analysis softwareAy105user account1Ay 105 Spring 2010 Experiment 8 2Setup The IRC-160 camera will need a fresh fill of its dewar with LN2. Use the“vented” funnel, and take care not to freeze any part of yourself with the nitrogen.Make sure that camera is connected and powered up (see p. C4 of the manual). Leavethe gain and offset controls at their default settings to start. The chip, if previouslywarm, takes several minutes to cool down. Two fills of the camera dewar are typicallyrequired to obtain a steady temperature.The camera has two outputs, a VGA video output and a parallel p ort. Whenthe camera was new back in the mists of the early 1990’s, a coal-burning PC witha dedicated parallel input card converted the camera output into data files. Now, a“modern” VGA-USB converter and software are used to capture images. The downsideof this is that captured images have (modest) add itional noise, and have a format of640×480, rather than the native 120×160 array size of the camera.Part A Measurements This is the time to explore, but wisely informed. Tryputting various objects in front of the camera – including yourself. Record your exper-iments and observations, using words, saved images, or both.In order to analyze your data, you will want to evaluate the response of the arrayto zero incident radiation. This is like a “bias” or reference frame, but in this casereally a combination of bias, dark current, and thermal background signal. It turnsout that finding a source of zero radiation is not easy in the thermal infrared. Thinkabout the problem at hand for a moment.One possible source of zero infrared energy would be a 100% reflectivity mirror,to force the camera to ”look” at its cold interior. Real mirrors are not that efficient,however. Using what you can find, which is probably a mirror with a roughly uniform97% reflectivity at room temperature, compute its effective temperature over the wave-length range the camera is sensitive. (That is, what temperature would a blackbodyneed to be to have the same power received by the detector?) There is a mirror/lenslabeled “Ge” around, which may be of some interest.One good source for a low background emitter is probably the cold side of the lidfrom the dewar, if it has been filled for a while, or the fill funnel. Experiment.Also explore the VGA2USB software application and learn how to save an im-age. Files are stored in .bmp or .jpg format. From the msdos command promptwindow, these files can be converted to .fits using Imagemagick’s convert XX.bmpYY.fits command. You can then run ds9 to display images on the PC. Check thatthe background level in a captured image is small and not negative. Adjust the offsetif necessary. Would it make sense to take an average of several images?Take your pick of observatory coffee mugs and walk around to the front hallwayof the Cahill lab floor to the kitchen area. Fill a coffee cup with water at roughly∼ 30◦C. In another coffee cup, use the microwave to heat the water. Go back toAy 105 Spring 2010 Experiment 8 3the lab, find the thermometer for calibration purposes, and take some images. Youmight want to image the cups up close but with the focus set to infinity (this tends toblur out detailed structure and give you a local average, which is what we want here).Take a frame or two of each source. Repeat this process for many different watertemperatures, as the heated cup cools, or as you warm up the room temperature cup.You may have to experiment with an appropriate temperature and distance from thecamera in order to not saturate the detector. Also, a quick Planck function calculationor estimation might save you some time. At the hot end the detector may have beensaturated. What happens if you slide e.g. a sheet of Plexiglas between the camera andthe coffee cup?Part A AnalysisUse your knowledge of IRAF to analyze images under Unix. Copy them over toyour own astro or the ay105user astro account using SS H Secure File Transfer.Using IRAF subtract the reference frame from each of the data frames. (It is agood idea to keep a copy of your raw images, in case you make a mistake.)We may be getting tired of this by now, but: Estimate the mean and standarddeviation for a ∼ 10 × 10 camera-pixel analysis box; try to make many measurementsover various regions, avoiding those with bad pixels. Get at least 10 of these, in areaswith different mean levels, and plot the mean vs. the variance. Compute the gain (inphotoelectrons per digital number)! Is the camera limited by photon (shot) noise?How does the signal change as a function of temperature? Does this correspondwith what you predict? As always, pay attention to errors.Part B Configuation Using knowledge of the lab equipment from previousexperiments, make yourself a spectrograph for infrared light. Use as a radiation sourcethe hot wire/lamp. You can set up as in the optical spectroscopy lab a collimatingmirror and a grating leading into the infrared camera but the configuration need notbe that complex. You might want th e collimator on a translational stage and you willdefinitely want to set the grating on top of a rotational