Ay 105 Lab Experiment #5: CCD Characteristics andOperationPurposeThis week you will study the characteristics of Charge Coupled Device (CCD)imaging array detectors. These detectors are the most commonly used in astronomy foroptical wavelength signal detection. In particular, you will learn about CCD quantumefficiency (QE) of CCDs in Parts A & B, empirically in Part A by measuring thereflective and transmissive properties of a detector, and theoretically in Part B bymodelling the solid state architecture and then the quantum efficiency. In Part C youwill investigate the electronic circuitry that operates a CCD and run the detector logiccontrol. Parts A & B can be done in one lab session. For the second session the twolab groups will join forces to work on the electronics part (C) in which you will operatean example set of readout electronics of a CCD detector.Pre-lab Work• Read the entire lab and skim the appendix!• Re-familiarize yourself with basic oscilloscope operation.BackgroundCCD quantum efficiency is usually measured with a setup including a QTH lamp,interference filters or a monochromator, lenses or an integrating sphere, and a cali-brated photodiode reference detector. Based on the week one experience in Ay105,you could probably create such a test setup and use it to measure QE as a function ofwavelength. After several hours spent making CCD exposures and photodiode currentmeasurements, you might derive a graph like one of those shown in Figure 1.In this lab, however, you will be investigating a slightly different and more inter-esting question: why do CCDs have the quantum efficiency variations with wavelengthshown in Figure 1? In particular, take special note of three characteristics of Figure1: (1) The peak response at wavelengths 6500˚A∼<λ∼<7000˚A. (2) The decrease inQE for wavelengths λ > 7000˚A. (3) The decrease in QE (and the wide variation fromdevice to device) at wavelengths λ < 5000˚A.1Ay 105 Spring 2011 Experiment 5 2Figure 1: QE vs. λ for various CCDs at Palomar Observatory.Equipment List63 mm Diameter, 356 mm EFL Achromat Lens80 mm f/2.8 triplet lensFilter HolderAluminum Mirror50 mm or 180 mm EFL Nikon LensTI 800x800 CCDCCD Fringe Program (on PC)computer files ...\CCD\SILICON.NDX and ...\CCD\SILICON.ABSOscilloscopeDigital MultimeterElastic Wrist StrapConductive Plastic MatCCD412 ChipLoral CCD Development Board2 Power SuppliesExperimentAy 105 Spring 2011 Experiment 5 3Part A: CCD Quantum EfficiencyPart A Setup. You will find a Texas Instruments 800 × 800, three-phase thinnedCCD glued between a pair of fused quartz plates. Take a moment to examine the CCD(both front and back), visually and through the low-power microscop e. Describe someof what you see and what you find most interesting in your lab notebook. Then installthe CCD sandwich in the filter holder, and place it on a rotating stage. Arrange thegreen HeNe (λ = 5348˚A) laser to shine on the CCD array.The experimental objective here is to measure the fractions of incident laser lightthat are transmitted and reflected upon striking the CCD array. “Thinned” CCDsare only about 8 − 10µm thick; the Si back surface also appears shiny, so it is notunreasonable to suppose that some photons reflect off of the surface and some photonsgo right through without being absorbed. Of course, photons in both of these categoriesstand no chance of being detected. The remaining fraction is thus an upper limit onthe quantum efficiency of the CCD:QE(λ) ≤ 1 − R(λ) − T (λ) .Your first task will be to determine how closely the actual CCDs in Figure 1 approachthe ideal case of detecting all photons which are not reflected or transmitted.You want to create an optical setup to collect the light transmitted straightthrough the array, and another optical lens assembly off-axis to reimage the reflectedlight on to the photodiode. Start with the laser on the left side of the table, illuminatingthe CCD in the middle of the bench; you will want to use the iris between the laserand CCD, stopped down, to block extraneous laser light from striking the CCD.Place an optical assembly to collect reflected light back from the CCD at ab out135 degrees from the laser path. You’ll need to rotate the CCD slightly away from thelaser beam’s normal incidence in order to collect the reflected beam; use the 63mmdiameter, 356 mm EFL achromatic lens to collect and collimate the reflected light oversome non-zero solid angle. (Notice that the 10 µm thick CCD “membrane” is not aprecisely flat surface, so the reflected beam will in general not be very well collimated).Then use the 80mm f/2.8 triplet lens to focus the collimated light, forming an imageof the point on the CCD form which the light was reflected.Part A Measurements. Locating this image and placing your photodiode atthis point will enable you to measure the amount of laser power reflected by the CCD.Determine whether or not you are likely to collect all of the reflected light by calculatingthe ratio of the image size (on the photodiod e) to the object size (the reflectin g spot onthe CCD), then estimate the latter and derive an estimate of the former for comparisonwith the 1 mm2photodiode area. Record the photodiode current generated by thelaser light reflecting from the CCD. (Note that the laser intensity varies, so monitorthe photodiode current for a while and estimate a likely uncertainty in all of yourAy 105 Spring 2011 Experiment 5 4measurements.)Next, slide the CCD sandwich within the filter holder so that the laser strikesonly the clear fused quartz plates, and measure the power reflected by the plates alone.Finally, substitute the diagonal mirror’s post for the CCD’s filter holder post and alignthe mirror so that the light strikes the photodiode.Measure the power reflected by the aluminum mirror. Bare Aluminum has areflectivity of 89% (could you determine this yourself, and if so, how accurately?),so from this you can determine the power in the laser beam incident on the CCDsandwich. Why is u sing the mirror a better approach than moving the photodiode sothat it intercepts the incident laser beam directly?Subtracting from this incident power the fraction reflected by the cover glassalone will enable you to d etermine the fraction that was reflected by the CCD itself.This is the fraction R(λ) in equation (1) at t he wavelength of the green laser.Now substitute the red laser for the green laser, and repeat these measurementsfor R(λ) at the