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 camera system. The camera / array is sensitive from∼ 2 − 4µm. In the first day of lab, you will acquire images of various infrared sourcesof interest, including a cooling cup of water, and analyze them on the computer. Inthe second part, you will set up a simple grating spectrograph and image the infraredspectrum of a hot wire seen through the atmosphere in a lab to examine features innear-infrared spectra.As there is a single camera, both groups can acquire the first set of images to-gether. On the second day, while one group is analyzing the first set of images, theother 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 dewarliquid n itrogenvented funnelplexiglassiceGe lensother toys2 coffee cups with water, one heatedthermometerpc and image analysis softwareAy105user accountlightbulb and postcollimating mirr or1Ay 105 Spring 2011 Experiment 8 2translational stagediffraction gratingrotational stageSetup 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 th e camera is connected and powered up (see p. C4 of the manual).Leave the gain and offset controls at their default settings to start. The chip, if pre-viously warm, takes several minutes to cool down. Two fills of the camera dewar aretypically required to obtain a steady temperature.The camera has two outputs, a VGA video output and a parallel port. 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) additional noise, and have a format of640×480, rather than the native 160×120 array size of the camera. The images are in”false color” with intensity mapped to color (as opposed to just greyscale in the CCDcamera image acquisition software). The defaults should be fi ne, but you may wish toexperiment with th e scaling via hardware settings on the camera.While the camera detector is cooling, sketch the experimental setup (includingcabling) in your notebook. Note the changing behavior of the output images as thetemperature drops.Part A Measurements This is the time to explore, but wisely informed. Tryputting various objects around the room in front of the camera – including yourself.Note the relative infrared intensity of objects made of different materials and/or opticalproperties (e.g. transparent vs opaque to the human eye). Record your experimentsand obser vations, using words, saved images, or both.Also explore the VGA2USB software application and learn how to save an image.Files are stored in .bmp or .jpg format. From the msdos command prompt window,these files can be converted to .fits using Imagemagick’s convert XX.bmp YY.fitscommand. You can then run ds9 to display images on the PC, or transfer them to theay105user account for this. Check that the background level in a captured image issmall and not negative. Adjust the offset if necessary. Would it make sense to take anaverage of several images?In order to analyze your data, you will want to evaluate the response of the arrayto zero incident radiation. It turns out that finding a source of zero radiation is noteasy in the thermal infrared. Think about the problem at hand for a moment. Insteadof the easily separable sources of instrumental background that could be measured forthe CCD camera, in this case your “reference frame” will be a combination of bias,dark current, and thermal background signal.Ay 105 Spring 2011 Experiment 8 3One 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 around the lab, which is probably a mirror with aroughly uniform 97% reflectivity at room temperature, compute its effective temper-ature over the wavelength range the camera is sensitive. (That is, what temperaturewould a blackbody need to be to have the same power received by the detector?) Thereis a lens/mirror labeled “Ge” around, which may be of some interest as it is particularlyreflective (80-95%) at wavelengths in the 2-3 µ m range. Note that it also has ∼50%transmission so you can test multiple effects depending on how you use it.Another good source for a low background emitter is probably the cold side ofthe lid from the dewar, if it has been filled for a while, or the fill funnel. Experiment.Remember your principles from the CCD-II lab in which you obtained opticalimages, and think about the types and numbers of images needed for this experiment.Also, check the dynamic range of the detector output by converting some test imagesfrom .b mp to .fits and examining them in ds9.When ready to move on, take your pick of observatory coffee mugs an d walkaround to the front hallway of the Cahill lab floor to the kitchen area. Fill a coffeecup with water at roughly 30◦C. In another coffee cup, use the microwave to heat thewater. Before doing so you may want to think about the relevant range of temperaturesto which the infrared camera is most sensitive, for example by doing a quick Planckfunction calculation. This will inform you as to how long you will have to wait fore.g. boiling water to start registering any changes across this wavelength range as itcools. Go back to the lab, find the thermometer for calibration purposes, and take someimages. At the hot end the detector may be saturated. At the cool end, the detectormay not sense anything above the thermal background of the lab environment. Recordyour by-eye observations regarding e.g. whether the mug is isothermal or exhibitstemperature gradients.Some advice is that you might want to image the cups up close but with the focusset to infinity (this tends to blur out detailed structure and give you a local