Technology for Submillimeter Astronomy

Despite about three decades of progress, the field of submillimeter astronomy remains quite challenging, because the detection technology is still under development and the transmission of the atmosphere is poor. The latter problem has been overcome by constructing submillimeter telescopes at excellent sites, first on Mauna Kea and later in Chile and Antarctica, and also by using airborne and space telescopes. Meanwhile, the improvements in technology over the past several decades have been remarkable. While considerable opportunities for improvement remain, existing detector and receiver technologies now often approach fundamental limits. This technological revolution has brought submillimeter astronomy from the fringes to the forefront of modern astrophysics and has stimulated major investments such as the 50-element ALMA interferometer and the ESA/NASA Herschel Space Observatory

Early Days of SIS Receivers

The modern era of millimeter and submillimeter spectral line observations and interferometry started at end of the 1979 with the invention of the Superconductor-Insulator-Superconductor (SIS) mixer. Tom Phillips co-invented this device while working at Bell Telephone Labs (BTL) in Murray Hill, NJ. His group built the first astronomically useful SIS heterodyne receiver which was deployed on the Leighton 10.4 m telescope at the Caltech Owens Valley Radio Observatory (OVRO) in the same year. Tom Phillips joined the Caltech faculty in the early 1980s where his group continues to lead the way in developing state-of-the-art SIS receivers throughout the millimeter and submillimeter wavelength bands. The rapid progress in millimeter and submillimeter astronomy during 1980s required developments on many fronts including the theoretical understanding of the device physics, advances in device fabrication, microwave and radio frequency (RF) circuit design, mixer block construction, development of wideband low-noise intermediate frequency (IF) amplifiers and the telescopes used for making the observations. Many groups around the world made important contributions to this field but the groups at Caltech and the Jet Propulsion Laboratory (JPL) under the leadership of Tom Phillips made major contributions in all of these areas. The end-to-end understanding and developments from the theoretical device physics to the astronomical observations and interpretation has made this group uniquely productive

THz Instruments for Space

Terahertz technology has been driven largely by applications in astronomy and space science. For more than three decades cosmochemists, molecular spectroscopists, astrophysicists, and Earth and planetary scientists have used submillimeter-wave or terahertz sensors to identify, catalog and map lightweight gases, atoms and molecules in Earth and planetary atmospheres, in regions of interstellar dust and star formation, and in new and old galaxies, back to the earliest days of the universe, from both ground based and more recently, orbital platforms. The past ten years have witnessed the launch and successful deployment of three satellite instruments with spectral line heterodyne receivers above 300 GHz (SWAS, Odin, and MIRO) and a fourth platform, Aura MLS, that reaches to 2520 GHz, crossing the terahertz threshold from the microwave side for the first time. The former Soviet Union launched the first bolometric detectors for the submillimeter way back in 1974 and operated the first space based submillimeter wave telescope on the Salyut 6 station for four months in 1978. In addition, continuum, Fourier transform and spectrophotometer instruments on IRAS, ISO, COBE, the recent Spitzer Space Telescope and Japan's Akari satellite have all encroached into the submillimeter from the infrared using direct detection bolometers or photoconductors. At least two more major satellites carrying submillimeter wave instruments are nearing completion, Herschel and Planck, and many more are on the drawing boards in international and national space organizations such as NASA, ESA, DLR, CNES, and JAXA. This paper reviews some of the programs that have been proposed, completed and are still envisioned for space applications in the submillimeter and terahertz spectral range

Review: far-infrared instrumentation and technological development for the next decade

Far-infrared astronomy has advanced rapidly since its inception in the late 1950s, driven by a maturing technology base and an expanding community of researchers. This advancement has shown that observations at far-infrared wavelengths are important in nearly all areas of astrophysics, from the search for habitable planets and the origin of life to the earliest stages of galaxy assembly in the first few hundred million years of cosmic history. The combination of a still-developing portfolio of technologies, particularly in the field of detectors, and a widening ensemble of platforms within which these technologies can be deployed, means that far-infrared astronomy holds the potential for paradigm-shifting advances over the next decade. We examine the current and future far-infrared observing platforms, including ground-based, suborbital, and space-based facilities, and discuss the technology development pathways that will enable and enhance these platforms to best address the challenges facing far-infrared astronomy in the 21st century

Development of the Submillimeter Band

This short article attempts to summarize my contribution to the field of submillimeter spectroscopy in the dense interstellar medium. It is taken mainly from my recollections and as a result some of the dates may be inaccurate. It covers most of the enabling receiver technology from frequencies of about 100 GHz to 2 THz and discusses the development of hot electron bolometers (HEB) and superconducting tunnel junction detectors (SIS). Many new molecular lines and some atomic lines have been revealed. These detectors are in use in the modern major projects such as ALMA and Herschel and will play their part in the many exciting projects of the next decade. Certainly one of the major contributions to the field has been the generation of many students who obtained Ph.D.s (14) and postdocs (25) in my group. The total number of national and international students who have obtained Ph.D.s (75) with use of the Caltech Submillimeter Observatory (CSO) and those who are currently studying using the CSO (44) is even more impressive

Infrared receivers for low background astronomy: Incoherent detectors and coherent devices from one micrometer to one millimeter

The status of incoherent detectors and coherent receivers over the infrared wavelength range from one micrometer to one millimeter is described. General principles of infrared receivers are included, and photon detectors, bolometers, coherent receivers, and important supporting technologies are discussed, with emphasis on their suitability for low background astronomical applications. Broad recommendations are presented and specific opportunities are identified for development of improved devices

Chasing Tom Phillips

This paper gives an informal and personal view of the major impact that Tom Phillips has had on the author’s scientific career and field of research