Session B20: Invited Session: Astronomy's Detectors and Physics Education

The basic physics of astronomical detectors, our eyes on the Universe

The universe is an amazingly huge place. While humankind has directly explored Earth's sister planets with space probes, we don't have the means to venture beyond the solar system, and so almost all information about the universe comes from sensing light that happens our way. Astronomy is constantly striving to find better ways to sense the feeble amount of energy from distant stars and galaxies. This quest has led to a new generation of large telescopes on the ground and in space. Possibly more important than the development of bigger telescopes is the rapid advancement in solid state detector technology. In the x-ray, visible and infrared wavelengths, the most advanced detectors are based on two fundamental technologies: (1) nearly perfect detector materials that efficiently convert photon energy to electrical charge, and (2) very sensitive transistors that convert a few electrons into a measurable voltage. This talk presents the basic physics of astronomical detectors and provides an introduction to the more specialized talks that follow in this session of presentations. Since detectors of light are critical to nearly every aspect of scientific research and involve a wide range of physical phenomena, this session of talks will provide the audience with physics lessons that can be readily incorporated in an undergraduate physics curriculum.   

Advanced CCD and CMOS image sensor technology at MIT Lincoln Laboratory

The Advanced Imaging Technology (AIT) program area at Lincoln Laboratory addresses a broad range of complex imaging problems by using a wide variety of silicon-based imager technologies, including charge-coupled devices (CCDs), active-pixel sensors (APSs), photodiode arrays, and Geiger-mode avalanche-photodiode (GMAPD) arrays that are single-photon sensitive. Many of these devices, including some very large imaging devices that require low defect levels, are fabricated by us from silicon wafers in our class-10 Microelectronics Laboratory. We also operate a fully equipped packaging facility that is capable of developing and performing innovative device packaging of imaging (and other) devices. In this talk, we present an overview of Lincoln Laboratory's image sensor technologies, describe how they work and how they are built. We discuss several imaging device parameters can be optimized for high sensitivity. These include quantum efficiency (including fill-factor), charge-transfer efficiency (moving the charge from the pixel to the output port without loss or added spurious charge), and the noise to read this charge out. The overall goal is to convert most or all of the photons that impinge on the device to photoelectrons and then to read out these photoelectrons without losing any and without adding read noise. Further, we will describe design elements or methods that can help with different specific applications: the orthogonal-transfer CCD (OTCCD), an electronic shutter for back illuminated imagers, the Geiger-mode avalanche photodiode (GMAPD) circuit element, and three-dimensionally integrated CMOS focal planes. Several examples of application to high-sensitivity, high-speed, and broad-wavelength range problems will presented.   

Gamma-ray Bursts, Black Holes, and Exoplanets: How CCD Detectors have Revolutionized Astronomy

I will tell the story of my research group's role in the development of astronomical charge-coupled detectors (CCDs) by relating the contributions of four MIT research students to projects which we have undertaken together over the past three decades. These projects have empowered observations extending over four decades of the electromagnetic spectrum, enabling discoveries ranging from gamma-ray burst emitting collapsars at cosmological distances, to accretion-driven black holes in the Galaxy, and to exoplanets in the solar neighborhood. This story will illustrate the key contributions which student researchers can make when a novel detector technology arrives on the scene. Finally, I will also describe some of the ways in which their early education in these possibilities has impacted my students' future careers as astronomers and experimental physicists.   

Coupling physics to understanding the performance of detector arrays

Over the last few decades developments in microelectronics have led to the development of arrays of detectors that can be used to measure unprecedentedly small levels of signal. Such arrays have been used over to detect electromagnetic radiation ranging in energy from the X-ray through sub-millimeter wavelengths and also particles. Perhaps nowhere have the improvements been more astonishing than in devices available for the visible part of the spectrum (400 -- 1000 nm). The most successful detector array in this spectral region is the Charge Coupled Detector (CCD) whose inventors were recognized with the Nobel Prize in Physics in 2009. In this talk I will review some of the detectors and technologies that are used in low light level imaging. I will also describe a full year sequence of classes (i.e. a theory class, a CCD camera building class and a CCD camera performance measurement class) that students at the Rochester Institute of Technology can take to make them knowledgeable as to the physics underlying the operation and performance of such detector arrays. Finally I will discuss the associated laboratory classes that students must take to measure the performance of the camera they have built and what aspects of fundamental physics are integrated into their understanding. These classes have been taken by both calculus and non-calculus trained students. The classes appeal to students with both types of backgrounds as it couples an understanding of Physics to something that they have built and use.   

Detecting the Cosmic Microwave Background at the Frontier of Cosmology and in the Classroom

The 3K blackbody Cosmic Microwave Background (CMB), while exceedingly faint, is the most abundant light in the Universe, permeating all of space as a relic of the hot, dense, primordial fireball. Its detection in 1965 established the Big Bang as the standard model of cosmology and earned its co-discoverers Penzias and Wilson a Nobel Prize. Over the past two decades, advances in detector technology driven by CMB research have produced telescopes with ever-increasing numbers of photon background-limited microwave detectors, capable of mapping fine structure of the CMB to micro-Kelvin precision. These have had enormous impact, determining the geometry of the universe, quantifying the dark matter and dark energy that dominate it, and detecting the faint polarization arising from the primordial seeds of structure. The current frontier is defined by new arrays of thousands of superconducting, polarized detectors producing maps approaching nano-Kelvin precision. In this decade, these measurements will answer questions about the physics driving the earliest moments of the Big Bang and will survey the large-scale structure of the universe, determining neutrino masses and constraining the nature of dark energy. The advanced detector technology fueling this frontier provides superb device-physics training for graduate students and postdocs working on current-generation CMB telescopes. At the same time, careful experimental techniques developed for CMB observations can now be combined with inexpensive high-quality satellite TV detectors to allow even undergraduates to detect the CMB, reproducing Penzias and Wilson's famous discovery. I describe one such undergraduate class at Harvard, which builds CMB telescopes from scratch in a few weeks with a modest budget, teaching students about microwave techniques and detectors and allowing them to find their own evidence for the Big Bang.