A Novel Reflectometer for Relative Reflectance Measurements of CCDs

摘要

The high quantum efficiencies (QE) of backside illuminated charge coupleddevices (CCD) has ushered in the age of the large scale astronomical survey.The QE of these devices can be greater than 90 %, and is dependent upon theoperating temperature, device thickness, backside charging mechanisms, andanti-reflection (AR) coatings. But at optical wavelengths the QE is wellapproximated as one minus the reflectance, thus the measurement of the backsidereflectivity of these devices provides a second independent measure of theirQE. We have designed and constructed a novel instrument to measure the relativespecular reflectance of CCD detectors, with a significant portion of thisdevice being constructed using a 3D fused deposition model (FDM) printer. Thisdevice implements both a monitor and measurement photodiode to simultaneouslycollect incident and reflected measurements reducing errors introduced by therelative reflectance calibration process. While most relative reflectometersare highly dependent upon a precisely repeatable target distance for accuratemeasurements, we have implemented a method of measurement which minimizes theseerrors. Using the reflectometer we have measured the reflectance of two types ofHamamatsu CCD detectors. The first device is a Hamamatsu 2k x 4k backsideilluminated high resistivity p-type silicon detector which has been optimizedto operate in the blue from 380 nm - 650 nm. The second detector being a 2k x4k backside illuminated high resistivity p-type silicon detector optimized foruse in the red from 640 nm - 960 nm. We have not only been able to measure thereflectance of these devices as a function of wavelength we have also sampledthe reflectance as a function of position on the device, and found a reflectiongradient across these devices.