352 Pages
    by CRC Press

    367 Pages 16 Color & 163 B/W Illustrations
    by CRC Press

    A Powerful Window into Cosmic Evolution

    Terahertz (THz) observations of interstellar atoms, molecules, and dust serve as powerful probes of the conditions within the interstellar medium that permeates our galaxy, providing insights into the origins of stars, planets, galaxies, and the Universe. Taking a cross-disciplinary approach to the subject, Terahertz Astronomy explores THz astrophysics and the technologies that make this rapidly evolving field possible.

    The first four chapters of the book discuss the origin and interpretation of THz light in astrophysical sources. The remaining five chapters present an overview of the technologies used to collect and detect THz light. Every chapter contains worked-out examples and exercises. The author explains each topic as intuitively as possible and includes the equations needed for real-life astrophysical applications.

    In just a few years, the number of active THz researchers has substantially grown due to increased interest in terrestrial remote sensing at THz frequencies. This book provides researchers with both the background science and technology to interpret THz observations and design, build, and deploy THz astronomical instrumentation.

    The Interstellar Medium at Terahertz Frequencies
    Introduction
    ISM Components of the Milky Way
    Lifecycle of the ISM
    Probing the Lifecycle of the ISM
    THz SEDs
    Conclusion

    THz Radiative Transfer Basics and Line Radiation
    Equation of Radiative Transfer
    Solution to the Equation of Radiative Transfer under LTE (Local Thermodynamic Equilibrium)
    Radiative Transfer of Rotational Transitions of Linear Molecules in LTE
    Non-LTE Approach
    Conclusion

    THz Continuum Emission
    Introduction
    THz Spectral Energy Distributions
    Deriving Dust Optical Depth, Column Density, and Mass
    Temperature and Density Distributions
    Dust Energy Balance in Clouds
    Dust–Gas Coupling
    Dust Polarization: Origin and Measurement
    Conclusion

    Simple Radiative Transfer Model
    Introduction
    Geometry
    Source Physical Conditions
    Lines of Sight
    Model Equation of Transfer
    LTE Radiative Transfer with Hydrodynamic Simulations
    Non-LTE Radiative Transfer with Hydrodynamic Simulations
    Going Further

    THz Optical Systems
    Introduction: Source-Beam Coupling
    QED and Maxwell
    Origin of a Single-Aperture Diffraction Pattern (QED)
    Gaussian Beam Optics
    Focusing Gaussian Beams
    Intercepting Gaussian Beams
    Illuminating THz Telescopes
    Conclusion

    THz Coherent Detection Systems
    Introduction
    Superheterodyne Receivers
    Receiver Noise Temperature
    Noise Temperature of THz Optical Systems
    THz Mixer Architectures and Noise
    IF Amplifiers
    Effective Temperature Measurement of THz Components
    THz Mixers
    THz Local Oscillators
    Receiver Back-Ends
    Receiver Stability and Allan Time
    Heterodyne Array Considerations
    Summary

    Incoherent Detectors
    Introduction
    Bolometer Basics
    Semiconductor Bolometers
    Superconducting Incoherent
    Background Noise Limited Operation
    Instrument Noise Limited Operation
    Sensitivity Requirements
    Comparing Heterodyne and Incoherent Detector Sensitivity
    Incoherent Array Considerations
    Conclusion

    THz Observing Techniques
    Introduction
    Observing Strategies
    Receiver Calibration
    Estimating Atmospheric Optical Depth
    THz Brightness Temperature of Planetary Bodies
    Conclusion

    THz Interferometry
    Introduction
    Simple Adding Interferometer
    Phase Switched Interferometer
    Correlation Interferometer
    Phasor Equation for Interferometry
    Aperture Synthesis of Extended Sources
    Filling-in uv Space
    Transforming the Visibility Function
    Map Noise Level
    Phase Closure or Self-Calibration
    Phase Error at THz Frequencies

    Answers to Problems

    Appendix 1: Timeline of Thz Technology
    Appendix 2: More Thz Transitions of Atoms and Molecules
    Appendix 3: Commonly Used Physical and Astronomical Quantities
    Appendix 4: Useful Radiative Transfer Expressions
    Appendix 5: Commonly Used Quasi-Optical Expressions
    Appendix 6: Useful Heterodyne Receiver Expressions

    References appear at the end of each chapter.

    Biography

    Christopher K. Walker is a Professor of Astronomy and an Associate Professor of Optical Sciences and Electrical & Computer Engineering at the University of Arizona. He has over 30 years of experience designing, building, and using state-of-the-art receiver systems for THz astronomy. He is the author of numerous papers on star formation and protostellar evolution, a topical editor for IEEE Transactions on TeraHertz Science and Technology, and the principal investigator of the long-duration balloon project "The Stratospheric THz Observatory (STO)" funded by NASA.

    "The book is beautifully illustrated, having a long list of references and worked examples at the end of each chapter. I would recommend the book to students and researchers working in THz technologies and astronomy."
    Optics & Photonics News, January 2016

    "This comprehensive, well-written book was a pleasure to read, an absolute must for anyone interested in learning about cutting-edge technologies and techniques revolutionizing our modern view of the Universe, and it is destined to become a standard reference work for astronomers and technologists."
    —Professor Glenn White, The Open University

    "This excellent book fills a huge hole in the literature in observational terahertz astronomy. No other existing text covers the essentials of terahertz astronomy instrumentation and techniques as applied to the study of the interstellar medium. It is sure to become an essential text for those who work in the field."
    —Christopher Groppi, School of Earth and Space Exploration, Arizona State University

    "… a wonderful book, combining an insightful overview of the interstellar medium with a description of the most important techniques used to study this component of galaxies and how new stars form. It’s particularly timely, with the availability of powerful new tools, including the ALMA array, the SOFIA airborne observatory, and a range of planned and proposed suborbital and space missions in the terahertz range."
    —Paul F. Goldsmith, Jet Propulsion Laboratory, California Institute of Technology and Herschel Space Observatory

    "This valuable and well-written textbook by Professor Christopher Walker helps to fill a gap in the literature describing the interstellar medium at terahertz frequencies. There are very few textbooks that discuss the medium from the observer’s point of view, showing how to determine its physical parameters from the output of the detectors. Also discussed are the operations of mixer and bolometer detectors."
    —Thomas G. Phillips, John D. MacArthur Professor of Physics Emeritus, California Institute of Technology

    "… a fundamental source for astronomers and engineers who wish to understand the physical principles and detection techniques."
    —Jonathan Williams, University of Hawaii

    "Walker’s book is incredibly timely: it introduces the basics of terahertz data but also explains the instrumentation at the level all observers need to know, and does so in friendly but, most importantly, crystal-clear prose."
    —George H. Rieke, Regents' Professor of Astronomy, University of Arizona

    "… an essential resource for all astrophysicists and experimental physicists seeking to exploit the opportunities of this last frontier in astronomy."
    —Michael Burton, University of New South Wales

    "The first four chapters that cover stellar evolution, atomic physics and radiation physics are the basics…. The last five are… crucial as THz data are highly dependent on the observation and calibration techniques, especially the detector technology, the improvement of which is the reason why the field has moved forward the way it is… the examples and exercises will help the readers along the way."
    Contemporary Physics (Aug 2016)