AY 105 Lab Experiment #6: CCD Characteristics II: Image Analysis Purpose: In this lab, you will continue investigating the properties of CCDs that you started in Experiment #5. The CCD enables measurement of both the number of photons and the position where they hit, giving spatial information. Placing a CCD at the focus of a telescope or behind a camera lens allows it to detect and record images, i.e. pictures. This lab is designed to give you experience in characterizing a two-dimensional CCD detector plus amplifier in terms of read noise, bias, dark current, system gain, bad pixels, linearity/saturation, and flat fields. As we have only one experimental setup, both groups will work together on acquiring data during the first lab period. The second may be spent on data “reduction”; these steps are outlined below in italics. Background: A charge coupled device or “CCD” is an array of millions of pixels each sensitive to photons. Photons enter the CCD and are absorbed by a silicon layer. This absorption excites an electron from the silicon’s valence band to its conduction band in a process known as the photoelectric effect. These “photo-electrons” are then captured and stored by applying a positive voltage to the pixel to hold the electrons in a potential well. The varying number of electrons stored in each pixel produces different voltages across the pixel that is measured (by a fast voltmeter) and the voltage converted to a digital number (DN) that is presented as “counts” or ADUs (analog-to-digital units). The ability to detect a signal depends on the relative strengths of the signal and overall noise present on the detector. For our purposes, noise will be quoted as the standard deviation of a signal. There are several types of noise in a CCD. Shot noise is noise that is associated with events that occur with constant arrival rates. (i.e. the photons collected by the telescope and the electrons detected by the CCD). Shot noise follows Poisson statistics, and it can be estimated by the signal in the units of the events recorded at the detector. Note that the events themselves are quantized in electrons (not ADU!). However, as discussed in lecture, the readout electronics that convert electrons detected at the CCD to digital numbers (DN or ADU) that are stored in the image by way of the gain present additional noise sources. Specifically, the read noise is the average error contributed to a pixel value by the amplifier used to measure the number of electrons contained in the pixel. Thus there is noise associated with the signal that arrives on the detector and noise associated with the detection of that signal. To make effective use of a CCD, its noise sources must be understood and calibrated.Equipment: - Black box containing diffuser, filter, and test pattern - Apogee Alta CCD Camera (borrowed from COO engineer Anna Moore) - Maxim analysis software (on right-side PC) Setup: We will be using a science grade CCD detector that was recently used on the Antarctica plateau. It is an Apogee Alta detector that runs under the Maxim software, installed on the right-side PC in the lab. To see a brief description of its duties as one of the “Gattini” test cameras click here: http://mcba11.phys.unsw.edu.au/~plato/gattini.html OR http://spacefellowship.com/news/art12078/camera-at-south-pole-to-determine-if-its-night-sky-is-ideal-for-new-telescope.html . (Note that you may have to type in the part of the url beyond the line break.) CCD detectors are very sensitive to light. To achieve accurate and reproducible results, a change is required in the experimental methods generally used thus far, where optics and detectors were used in the open. To reduce as much as possible the stray light reaching the CCD, in this lab the detector is located on top of a (more or less) light-tight enclosure, and is mounted in a “down-looking” fashion, (perhaps with duct tape, in Ay105 fashion). The detector is cooled by a thermoelectric cooler (TEC), which takes about 5 minutes to cool the CCD to a stable equilibrium. Thus, the first thing you should do is to start up the CCD control software and make sure the CCD is cooling. The Maxim program has two windows: a small window with several tabs and a larger display window where your images will appear. Check to see that the camera itself has the power cable connected, and that the transformer is plugged in (if the fan is running, all is well here). Also verify that the camera is connected to the PC; to initialize the camera operation, go to the Setup tab and click Connect. Then, set an initial temperature of -20 C (on one of the tabs). At any time the software displays numbers like -20 / 75 %. This is a reading of the CCD temperature in C, and the percentage of the total available cooling power that is being applied to the CCD. After you set a new temperature, you will see these numbers change a lot, and you may notice that the approach to the set temperature is under-damped. It oscillates about the set temperature for a while before settling down, and takes about 5 minutes to fully settle.Other relevant parts of the software menu that you may find useful are the following: Also note that there is a known bug in the software display: if an image is taken such that the window is saturated (65535 ADU = [216 – 1] where our ADC is 16-bit), you must close all the image windows then expose again. If you do not, the successive images will appear to be saturated, even if the CCD is covered properly. Please note this, in case you run into any mystery behavior as you acquire data. File - Settings: Change to Unsigned Number Format? File - Setup Header: Change variables that are written to the fits header. View - CCD Control Window: Setup: Connect, Cooler On, Warm Up, Disconnect Focus: Used to continually display images Sequence: Save a batch of images! Settings: define a subframe or binning Expose: Type=Light, Bias, Dark Set exposure time and delay View - Screen Stretch Window: View - Information Window: !Once the detector is cooling, look inside at the layout of the optics inside this “black box" and sketch/explain this in your lab notebook. You may remove the red screws on the top and lift the handle to reveal the diffuser / filter / test pattern located inside the enclosure. Check to make sure that the test pattern is