I present concepts and methods for evaluating infrared camera systems. The individual components of camera systems are fairly well understood, but the system is more than the sum of its parts. Many of the usual techniques for measuring individual photodetectors are inapplicable to pixels which are permanently bonded to a readout circuit and cannot otherwise be accessed. Similarly, understanding the eventual sensitivity of the system requires understanding how the signal propagates through the various interacting components. Measuring the sensitivity requires techniques for finding characteristics which are internal to the device and cannot be directly measured. I describe all of these considerations and present techniques for measuring the behavior of any camera system.I also show how a camera system can be used as a powerful testbed for investigating the underlying physics of a given photodetector technology. Thousands of pixels can be simultaneously measured, allowing characterization in terms of a statistically large number of photodetectors rather than only a few individual devices. Additionally, different designs can be fabricated within the same camera in order to directly compare their behavior. I use camera characterization techniques to develop a better understanding of one specific photodetector technology, namely indium-gallium-arsenide (InGaAs) heterojunction phototransistors. In addition to a general theory, I present my evaluation of my lab’s ongoing project to use this phototransistor technology to build a high-speed, high-sensitivity near-infrared camera system. We were given a grant by the Keck Foundation to develop a camera for SCExAO, a ground-based coronagraph system at the Subaru telescope for exoplanet direct imaging. Direct imaging of a planet is limited by the ability of the coronagraph to block the light of the much brighter host star, which in turn is limited by the performance of the cameras which correct for vibration and atmospheric turbulence. When our project began, we believed our camera could be improved to the point where it would out-perform existing cameras and permit detection of exoplanets at closer orbital radii around their host stars, as well as detection of exoplanets with lower masses, than was previously possible. I developed models of the camera and methods for evaluating its performance to determine whether we could meet this goal. I conclude that the phototransistor technology is inherently sensitive enough, but the pixels have a poor fill factor and thus cannot collect enough light to make use of that sensitivity. In practice, our phototransistor cameras are not yet developed enough to contribute to exoplanet observations.

Creator

• Rabinowitz, Jacob

DOI

• https://doi.org/10.21985/n2-tw0c-kr81

Subject

• Astrophysics
• Physics

Language

• en

Alternate Identifier

• etdadmin_upload_899503
• http://dissertations.umi.com/northwestern:16022

Keyword

• Instrumentation

Date created

• 2022-01-01

Resource type

• Dissertation

Rights statement

• In Copyright