Photodetectors

In this book some recent advances in development of photodetectors and photodetection systems for specific applications are included. In the first section of the book nine different types of photodetectors and their characteristics are presented. Next, some theoretical aspects and simulations are discussed. The last eight chapters are devoted to the development of photodetection systems for imaging, particle size analysis, transfers of time, measurement of vibrations, magnetic field, polarization of light, and particle energy. The book is addressed to students, engineers, and researchers working in the field of photonics and advanced technologies

Instrument Design and Radiation Pattern Testing for Terahertz Astronomical Instruments

abstract: The Milky Way galaxy is a powerful dynamic system that is highly efficient at recycling material. Stars are born out of intergalactic gas and dust, fuse light elements into heavier elements in their cores, then upon stellar death spread material throughout the galaxy, either by diffusion of planetary nebula or by explosive events for high mass stars, and that gas must cool and condense to form stellar nurseries. Though the stellar lifecycle has been studied in detail, relatively little is known about the processes by which hot, diffuse gas ejected by dying stars cools and conglomerates in the interstellar medium (ISM). Much of this mystery arises because only recently have instruments with sufficient spatial and spectral resolution, sensitivity, and bandwidth become available in the terahertz (THz) frequency spectrum where these clouds peak in either thermal or line emission. In this dissertation, I will demonstrate technology advancement of instruments in this frequency regime with new characterization techniques, machining strategies, and scientific models of the spectral behavior of gas species targeted by these instruments. I begin this work with a description of radiation pattern measurements and their use in astronomical instrument characterization. I will introduce a novel technique to measure complex (phase-sensitive) field patterns using direct detectors. I successfully demonstrate the technique with a single pixel microwave inductance detectors (MKID) experiment. I expand that work by measuring the APEX MKID (A-MKID) focal plane array of 880 pixel detectors centered at 350 GHz. In both chapters I discuss the development of an analysis pipeline to take advantage of all information provided by complex field mapping. I then discuss the design, simulation, fabrication processes, and characterization of a circular-to-rectangular waveguide transformer module integrated into a circularly symmetric feedhorn block. I conclude with a summary of this work and how to advance these technologies for future ISM studies.Dissertation/ThesisDoctoral Dissertation Exploration Systems Design 201

The 2017 Terahertz Science and Technology Roadmap

Science and technologies based on terahertz frequency electromagnetic radiation (100GHz-30THz) have developed rapidly over the last 30 years. For most of the 20th century, terahertz radiation, then referred to as sub-millimeter wave or far-infrared radiation, was mainly utilized by astronomers and some spectroscopists. Following the development of laser based terahertz time-domain spectroscopy in the 1980s and 1990s the field of THz science and technology expanded rapidly, to the extent that it now touches many areas from fundamental science to “real world” applications. For example THz radiation is being used to optimize materials for new solar cells, and may also be a key technology for the next generation of airport security scanners. While the field was emerging it was possible to keep track of all new developments, however now the field has grown so much that it is increasingly difficult to follow the diverse range of new discoveries and applications that are appearing. At this point in time, when the field of THz science and technology is moving from an emerging to a more established and interdisciplinary field, it is apt to present a roadmap to help identify the breadth and future directions of the field. The aim of this roadmap is to present a snapshot of the present state of THz science and technology in 2016, and provide an opinion on the challenges and opportunities that the future holds. To be able to achieve this aim, we have invited a group of international experts to write 17 sections that cover most of the key areas of THz Science and Technology. We hope that The 2016 Roadmap on THz Science and Technology will prove to be a useful resource by providing a wide ranging introduction to the capabilities of THz radiation for those outside or just entering the field as well as providing perspective and breadth for those who are well established. We also feel that this review should serve as a useful guide for government and funding agencies

Optical Microring Resonators for Photoacoustic Imaging and Detection.

This work is to utilize the superior characteristics of polymer microring resonators in ultrasound detection to push the application of photoacoustic imaging to an entirely new level. We first demonstrated significantly improved imaging quality for photoacoustic tomography (PAT) using microring detectors. For wideband PAT, the microring detectors were able to faithfully detect both the boundaries and the inner structure, while piezoelectric detectors can only preserve one of the two aspects. For high-resolution PAT over a large imaging area, we imaged 50 µm black beads and found that microrings produced high-resolution imaging over a 16-mm-diameter imaging area while the 500 µm piezoelectric detectors only obtained high-resolution imaging over a small area around center. Pure optical photoacoustic microscopy (PAM) has been demonstrated. Microring ultrasonic resonators were applied in in vivo photoacoustic imaging for the first time. Good imaging signal-to-noise ratio and high axial resolution of 8 µm were calibrated. As a comparison, a commercial hydrophone with similar sensitivity produced a low axial resolution of 105 µm. A 5 mm miniaturized probe consisting of a fiber to deliver excitation laser pulses and microring detectors for ultrasound detection has been fabricated for photoacoustic endoscopy. The calibrated high radial resolution of 21 µm was higher than other types of endoscopic photoacoustic probes, around 40 µm or larger. A photoacoustic correlation spectroscopy (PACS) technique was proposed. In a proof-of-concept experiment, we demonstrated low-speed flow measurement of ~15 µm/s by the PACS technique. We also demonstrated in vivo flow speed measurement of red blood cells in capillaries in a chick embryo model by PACS. Other techniques might have difficulties to measure it due to the low signal contrast and/or poor resolutions. We also proposed terahertz electromagnetic pulse detection by photoacoustic method. We used carbon nanotube composites as efficient photoacoustic transmitters and microrings as sensitive detectors. The photoacoustic method provides low-cost and real-time terahertz detection (~µs), which is difficult by conventional terahertz detectors, such as a bolometer or a pyroelectric detector.Ph.D.Electrical EngineeringUniversity of Michigan, Horace H. Rackham School of Graduate Studieshttp://deepblue.lib.umich.edu/bitstream/2027.42/91497/1/chensll_1.pd

Terahertz Technology and Its Applications

The Terahertz frequency range (0.1 – 10)THz has demonstrated to provide many opportunities in prominent research fields such as high-speed communications, biomedicine, sensing, and imaging. This spectral range, lying between electronics and photonics, has been historically known as “terahertz gap” because of the lack of experimental as well as fabrication technologies. However, many efforts are now being carried out worldwide in order improve technology working at this frequency range. This book represents a mechanism to highlight some of the work being done within this range of the electromagnetic spectrum. The topics covered include non-destructive testing, teraherz imaging and sensing, among others