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

Thermal Monitoring: Raman Spectrometer System for Remote Measurement of Cellular Temperature on a Microscopic Scale

A simple setup was demonstrated for remote temperature monitoring of water, water-based media, and cells on a microscopic scale. The technique relies on recording changes in the shape of a stretching band of the hydroxyl group in liquid water at 3,100-3,700 cm^(-1). Rather than direct measurements in the near-infrared (IR), a simple Raman spectrometer setup was realized. The measured Raman shifts were observed at near optical wavelengths using an inverted microscope with standard objectives in contrast to costly near-IR elements. This allowed for simultaneous visible inspection through the same optical path. An inexpensive 671-nm diode pump laser (<100 mW), standard dichroic and lowpass filters, and a commercial 600-1,000 nm spectrometer complete the instrument

THz in biology and medicine: toward quantifying and understanding the interaction of millimeter- and submillimeter-waves with cells and cell processes

As the application and commercial use of millimeter- and submillimeter-wavelength radiation become more widespread, there is a growing need to understand and quantify both the coupling mechanisms and the impact of this long wavelength energy on biological function. Independent of the health impact of high doses of radio frequency (RF) energy on full organisms, which has been extensively investigated, there exists the potential for more subtle effects, which can best be quantified in studies which examine real-time changes in cellular functions as RF energy is applied. In this paper we present the first real time examination of RF induced changes in cellular activity at absorbed power levels well below the existing safe exposure limits. Fluorescence microscopy imaging of immortalized epithelial and neuronal cells in vitro indicate increased cellular membrane permeability and nanoporation after short term exposure to modest levels (10-50 mW/cm2) of RF power at 60 GHz. Sensitive patch clamp measurements on pyramidal neurons in cortical slices of neonatal rats showed a dramatic increase in cellular membrane permeability resulting either in suppression or facilitation of neuronal activity during exposure to sub-μW/cm2 of RF power at 60 GHz. Non-invasive modulation of neuronal activity could prove useful in a variety of health applications from suppression of peripheral neuropathic pain to treatment of central neurological disorders

Impact of Low Intensity Millimeter-Waves on Cell Membrane Permeability

As the applications and commercial uses of millimeter- and submillimeter-waves grow, we should take a more detailed look at the impact this frequency range has on biological systems. This paper examines one specific effect of low-level (10-50 times the MPE - maximum permissible exposure) 60 GHz CW RF power on cells – the opening of voltage sensitive cation channels

Interpreting Flux from Broadband Photometry

We discuss the transformation of observed photometry into flux for the creation of spectral energy distributions and the computation of bolometric luminosities. We do this in the context of supernova studies, particularly as observed with the Swift spacecraft, but the concepts and techniques should be applicable to many other types of sources and wavelength regimes. Traditional methods of converting observed magnitudes to flux densities are not very accurate when applied to UV photometry. Common methods for extinction and the integration of pseudo-bolometric fluxes can also lead to inaccurate results. The sources of inaccuracy, though, also apply to other wavelengths. Because of the complicated nature of translating broad-band photometry into monochromatic flux densities, comparison between observed photometry and a spectroscopic model is best done by comparing in the natural units of the observations. We recommend that integrated flux measurements be made using a spectrum or spectral energy distribution which is consistent with the multi-band photometry rather than converting individual photometric measurements to flux densities, linearly interpolating between the points, and integrating. We also highlight some specific areas where the UV flux can be mischaracterized.Comment: Accepted for publication in the Astronomical Journal. 16 pages, 9 figures. A PDF file with wide-screen friendly figures is linked from this blog post http://ultravioletsupernova.blogspot.com/2016/08/interpreting-flux-from-broadband.htm

Sir Jagadis Chunder Bose: Traversing the interdisciplinary gap between physics and biology

Sir Jagadis Chunder Bose was a prolific and inventive experimental scientist. Born in what is now Bangladesh in 1858, his scientific career spanned more than 30 years and included a degree in natural sciences from Christ College, Cambridge, and a doctorate from the University of London in 1884. He studied under the likes of Lord Rayleigh, Sir James Dewar, and the great naturalist, Francis Balfour. In 1885, under great controversy, Bose assumed a faculty post in physics at Presidency College, Calcutta, India and remained there until his retirement in 1915. In 1917, he founded the institute which still bears his name and stayed technically active well into his 70s. At first, working with his own funds and only a tin smith, he managed to assemble the most sophisticated Hertzian wave apparatus of his day, and in only ten years, his fame had spread throughout Europe

Terahertz Technology in Outer and Inner Space

After more than 30 years of niche applications in the space sciences area, the field of Terahertz Technology is entering a true Renaissance. While major strides continue to be made in submillimeter wave astronomy and spectroscopy, the past few years have seen an unprecedented expansion of terahertz applications, components and instruments. Broad popular interest in this unique frequency domain has emerged for the first time, spanning applications as diverse as biohazard detection and tumor recognition. Already there are groups around the world who have ap-plied specialized Terahertz techniques to disease diagnostics, recognition of protein structural states, monitoring of receptor binding, performing label-free DNA sequencing and visualizing contrast in otherwise uniform tissue. A commercial terahertz imaging system has recently started tests in a hospital environment and new high sensitivity imagers with much deeper penetration into tissue have begun to emerge. Solicitations for more sophisticated instruments and enabling terahertz components have filtered into US agency proposal calls from DoD and NASA, to NSF and NIH, and many new research groups have sprung up, both in this country and in Europe and Asia. This presentation will broadly survey terahertz technology from its cradle applications in space science and spectroscopy to more recent biomedical and chemical uses

Ecosystem Engineering, Anthropogenic Landscapes, and Sea Level Changes Over 8000 Years of Human History in the Eastern Caribbean

Upon first arrival of humans to new places anthropogenic disturbances to landscapes commence. Later groups of different people or descendants of the original colonists will make yet additional modifications and so on through time, so that by today the landscape contains a cumulative record of anthropogenic history. We combined the interpretive frameworks of landscape and historical ecology to investigate the anthropogenic trajectories across nine islands of the southern and eastern Caribbean. Microfossils from a series of environmental cores reveal the shifting and cumulative humanization of landscapes from c. 8000 cal yr BP through early European colonial occupations in this region