Ay 105 Lab Experiment #8: Infrared Array CameraIn the final lab, you will study the characteristics of an InSb infrared array camera,and examine features in a near-infrared spectrum. In the first part, you will acquireimages of various infrared sources and analyze them on the computer. In the secondpart, you will measure a spectrum of a hot wire using a simple grating spectrograph.Both groups can acquire the first set of images together. Then, while one group isanalyzing the first set of images, the other group can obtain the wire spectrum images.Setup Fill the IRC-160 camera dewar with LN2. Use the “vented” funnel, andtake care not to freeze any part of yourself with the nitrogen. Connect and power upthe camera (see p. C4 of the manual). Leave the gain and offset controls at theirdefault settings to start. The chip, if previously warm, takes several minutes to cooldown.Part 1 We want to evaluate the response of the array to zero radiation (a “bias”or reference frame, really a combination of bias and background signal). Try puttingvarious objects in front of the camera–it turns out that finding a source of zero radiationis not easy, in the infrared. This camera is sensitive in the near-infrared from ∼ 2−4µm.What is the ratio of radiant energy at 4 microns between a 310 K and 77 K blackbody?One possible source of zero infrared energy might be a 100% reflectivity mirror, to forcethe camera to ”look” at its cold interior. Real mirrors are not that efficient, however.Compute the effective temperature, over the wavelength range the camera is sensitive,of a mirror with a uniform 97% reflectivity at room temperature. (That is, whattemperature would a blackbody need to be to have the same power received by thedetector?)One good source for a low background is probably the cold side of the lid fromthe red dewar, if it has been on for a while. Connect the computer to the camera andtake a reference frame:> read160 15 ref.bin> histo ref.binThe read160 command here will average 15 frames, and the histo command willshow you a pixel histogram. Check that the background level is small and not negative.Adjust the offset if necessary. Why do we want to average several frames here?Fill a coffee cup with water at 30◦C, and image the cup close up but with thefocus set to infinity (this tends to blur out detailed structure and give you a localaverage, which is what we want here). Use the microwave in the lab behind to heat1Ay 105 Spring 2008 Experiment 8 2the water. Take a frame or two here with read160 1 im1.bin of this source. Repeatthis process for many different water temperatures, stopping at the hot end when thedetector becomes saturated. What happens if you slide a sheet of Plexiglas betweenthe camera and the coffee cup?Analysis (can also be done after class if necessary)Use your knowledge of IRAF to analyze images under Unix. Copy them over tothe ay105 account using SSH Secure File Transfer.You will need to convert the images to the standard FITS format:% irtofits image.in image.outConvert each frame to FITS. Using IRAF subtract the reference frame from eachof the data frames. (It is a good idea to keep a copy of your raw images, in caseyou make a mistake.) Then, estimate the mean and standard deviation for a 10 × 10analysis box; try to make many measurements over various regions, avoiding those withbad pixels. Get at least 10 of these, in areas with different mean levels, and plot themean vs. the variance.How can you compute the gain (in photoelectrons per digital number) from thisdata? Is the camera limited by photon (shot) noise? How does the signal change as afunction of temperature? Does this correspond with what you predict?Part 2 Remove the coffee cup, and notice the spectrograph setup. The radiationfrom the hot wire/lamp is collimated by the mirror, then to the grating and into thecamera. (Set up any pieces that are not in place.) You’ll want to set the grating on topof a rotational stage so that you can make some accurate angle measurements. Whatdo you notice when the grating is directly facing the camera (β = 0)?Find the zero-order image and first-order spectrum of the wire lamp. Note thatyou may be able to see, with your eye, some optical light shining to the side of thecamera lens, with the (of course not visible) infrared spectrum entering at the center.You may need to put the Plexiglas at various positions (and/or walk around) to blockstray infrared light emitted by hot sources from entering the camera.Investigate the configuration and the spectrum of the wire lamp you see. Recordthe zero-angle of the grating (at which the camera sees its own reflection), the angleat which the zero order (reflection) appears at the array center, and the angle wherethe first order spectrum begins.Measure the position angles of any absorption lines (or sets of lines) you see, andalso the point where the spectrum cuts off. Identify the absorption lines with thosefrom the atmospheric