Special Libraries, April 1933

Volume 24, Issue 3https://scholarworks.sjsu.edu/sla_sl_1933/1002/thumbnail.jp

Terahertz detection: approaches and trade-offs

The development of faster and more sensitive detectors has been a major reason for the opening up of the THz spectral region. If only the amplitude of a THz wave is detected it is an incoherent or direct detector. When both the amplitude and phase are detected the detector is a coherent one. Coherent detection is not a direct process. In a heterodyne receiver, which is the most common coherent detector, detection is in two stages, with the incoming signal being 'mixed' with another signal, and it is the combination of both which is detected. In this lecture an overview will be presented about those incoherent and coherent detectors, which are used in many laboratories as weil as in space missions and other applications. The physics of the detection mechanism and major applications as weil as potential improvements will be presented. Finally, the trade-off between incoherent and coherent detection will be discussed

Application of Raman Spectroscopy as in situ Technology for the search for life

Raman microscopy is a nondestructive in situ technology appropriate to identify organic compounds and mineral products. It is a well-established technology and applied in various areas like pharmacy, biology, and mineralogy. Measurements could also be taken on other planetary bodies of our Solar System via future spacecrafts. The range for application reaches from acquiring discriminating bands (e.g., Raman reporter molecules like pigments) to the complex evaluation of spectral fi ngerprints. For the chemical characterization of biological samples as well as biomaterial-containing samples, chemometrical methods and pattern recognition need to be used for a reliable identi fi cation. Databases of Raman spectra established beforehand support the identi fi cation of the observed material. The ExoMars Mission in 2018 is the fi rst mission for which a Raman spectrometer is part of the planned payload. In preparation to this and further missions, it is necessary to study the circumstances one could be faced with when performing Raman measurements in a non-Earth-like environment. The differences and difficulties compared to the established measurement approaches on Earth (Sect. 2 ) need to be recognized, and solutions must be found. As an example for a space application in Mars exploration, the identification of b-carotene in cyanobacteria on Mars-analogue material by Raman spectroscopy is presented (Sect. 3 , based on Böttger et al., 2012 ) . A procedure was developed to optimize the detection of cyanobacteria embedded in different types of martian soils

Evidence of noncascade intracenter electron relaxation in shallow donor centers in silicon

Noncascade relaxation of photoexcited electrons on ionized donor centers has been observed in silicon doped by arsenic (Si:As) at low temperatures. Emission spectra of the Si:As terahertz intracenter laser give evidence of specific channels for the electron relaxation through low-lying donor states. The dominating relaxation channels strongly depend on the initial energy distribution of the nonequilibrium carriers. A relaxation step may exceed not only the energy gap to an adjacent lower-lying donor level but also the characteristic energy step as set by the energy and momentum conservation requirements for intravalley acoustic phonons.Kavli Institute of NanoscienceApplied Science

Terahertz Raman laser based on silicon doped with phosphorus

Raman-type stimulated emission at frequencies between 5.0 and 5.2?THz as well as between 6.1 and 6.4?THz has been realized in silicon crystals doped by phosphorus donors. The Raman laser operates at around 5?K under optical excitation by a pulsed, frequency-tunable infrared free electron laser. The frequencies of the observed laser emission are close to the frequencies of the intracenter laser lines which originate from the 2p0 and 2p± phosphorus states. The Stokes shift of 3.16?THz is equal to the difference between the energies of the phosphorus ground state, 1s(A1), and the 1s(E) excited state.Kavli Institute of NanoscienceApplied Science