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Parrott, E. P. J., Zeitler, J. A., Fris<cc><152>c<cc><152>ic<cc><81>, T., Pepper, M., Jones, W., Day, G. M., et al. (2009). Testing the sensitivity of terahertz spectroscopy to changes in molecular and supramolecular structure: a study of structurally similar cocrystals. Crystal Growth & Design, 9(3), 1452–1460.
Abstract: Terahertz time-domain-spectroscopy (THz-TDS) has emerged as a versatile spectroscopic technique, and an alternative to powder X-ray diffraction in the characterization of molecular crystals. We tested the ability of terahertz spectroscopy to distinguish between chiral and racemic hydrogen-bonded cocrystals that are similar in molecular and supramolecular structure. Terahertz spectroscopy readily distinguished between the isostructural cocrystals of theophylline with chiral and racemic forms of malic acid which are almost identical in molecular structure and supramolecular architecture. Similarly, the cocrystals of theophylline with chiral and racemic forms of tartaric acid, which are similar at the molecular level but dissimilar in crystal packing, were distinguished unequivocally. The investigation of the same cocrystals using X-ray powder diffraction and Raman spectroscopy suggested that THz-TDS is comparable in sensitivity to diffraction methods and more sensitive than Raman spectroscopy to changes in cocrystal architecture. The differences in spectra acquired by THz-TDS could be further enhanced by cooling the samples to 109 K.
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Lobanov, Y., Shcherbatenko, M., Shurakov, A., Rodin, A. V., Klimchuk, A., Nadezhdinsky, A. I., et al. (2014). Heterodyne detection at near-infrared wavelengths with a superconducting NbN hot-electron bolometer mixer. Opt. Lett., 39(6), 1429–1432.
Abstract: We report on the development of a highly sensitive optical receiver for heterodyne IR spectroscopy at the communication wavelength of 1.5 μm (200 THz) by use of a superconducting hot-electron bolometer. The results are important for the resolution of narrow spectral molecular lines in the near-IR range for the study of astronomical objects, as well as for quantum optical tomography and fiber-optic sensing. Receiver configuration as well as fiber-to-detector light coupling designs are discussed. Light absorption of the superconducting detectors was enhanced by nano-optical antennas, which were coupled to optical fibers. An intermediate frequency (IF) bandwidth of about 3 GHz was found in agreement with measurements at 300 GHz, and a noise figure of about 25 dB was obtained that was only 10 dB above the quantum limit.
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Soifer, B. T., & Pipher, J. L. (1978). Instrumentation for infrared astronomy. Annual Rev. Astron. Astrophys., 16(1), 335–369.
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Teich, M. C. (1968). Infrared heterodyne detection. In Proc. IEEE (Vol. 56, pp. 37–46). IEEE.
Abstract: Heterodyne experiments have been performed in the middle infrared region of the electromagnetic spectrum using the CO2laser as a radiation source. Theoretically optimum operation has been achieved at kHz heterodyne frequencies using photoconductive Ge:Cu detectors operated at 4°K, and at kHz and MHz frequencies using Pb1-xSnxSe photovoltaic detectors at 77°K. In accordance with the theory, the minimum detectable power observed is a factor of 2/η greater than the theoretically perfect quantum counter, hvΔf. The coefficient 2/η varies from 5 to 25 for the detectors investigated in this study. A comparison is made between photoconductive and photodiode detectors for heterodyne use in the infrared, and it is concluded that both are useful. Heterodyne detection at 10.6 µm is expected to be useful for communications applications, infrared radar, and heterodyne spectroscopy. It has particular significance because of the high radiation power available from the CO2laser, and because of the 8 to 14 µm atmospheric window.
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Gershenson, M. E., Gong, D., Sato, T., Karasik, B. S., & Sergeev, A. V. (2001). Millisecond electron-phonon relaxation in ultrathin disordered metal films at millikelvin temperatures. Appl. Phys. Lett., 79, 2049–2051.
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Ferrari, S., Kovalyuk, V., Hartmann, W., Vetter, A., Kahl, O., Lee, C., et al. (2017). Hot-spot relaxation time current dependence in niobium nitride waveguide-integrated superconducting nanowire single-photon detectors. Opt. Express, 25(8), 8739–8750.
Abstract: We investigate how the bias current affects the hot-spot relaxation dynamics in niobium nitride. We use for this purpose a near-infrared pump-probe technique on a waveguide-integrated superconducting nanowire single-photon detector driven in the two-photon regime. We observe a strong increase in the picosecond relaxation time for higher bias currents. A minimum relaxation time of (22 +/- 1)ps is obtained when applying a bias current of 50% of the switching current at 1.7 K bath temperature. We also propose a practical approach to accurately estimate the photon detection regimes based on the reconstruction of the measured detector tomography at different bias currents and for different illumination conditions.
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Käufl, H. U., Rothermal, H., & Drapatz, S. (1984). Investigation of the Martian atmosphere by 10 micron heterodyne spectroscopy. A&A, 136, 319–325.
Keywords: astronomical spectroscopy, atmospheric composition, infrared astronomy, mars atmosphere, spectral line width, carbon dioxide concentration, nonequilibrium thermodynamics, optical heterodyning, planetary radiation, mars, atmosphere, spectroscopy, atmosphere, carbon dioxide, altitude, kinetics, rotation, thermal properties, temperature, emissions, intensity, models, data, spectra
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Rothermel, H., Käufl, H. U., Schrey, U., & Drapatz, S. (1988). Thermal structure of the Martian mesosphere. A&A, 196, 296–300.
Keywords: atmospheric temperature, carbon dioxide, infrared spectroscopy, mars atmosphere, mesosphere, emission spectra, line spectra, spatial resolution, mars, atmosphere, mesosphere, structure, thermal properties, spectra, spectroscopy, earth-based observations, temperature, patterns, infrared, polar regions, wavelengths, equipment, procedure, carbon dioxide, emissions
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Johnson, M. A., Betz, A. L., McLaren, R. A., Townes, C. H., & Sutton, E. C. (1976). Nonthermal 10 micron CO2 emission lines in the atmospheres of Mars and Venus. A&A, 208, 145.
Keywords: carbon dioxide, emission spectra, infrared spectra, mars atmosphere, nonthermal radiation, optical heterodyning, planetary radiation, venus atmosphere, absorption spectra, energy transfer, line spectra, molecular absorption, molecular collisions, near infrared radiation, solar flux
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Rothermel, H., Käufl, H. U., & Yu, Y. (1983). A heterodyne spectrometer for astronomical measurements at 10 micrometers. A&A, 126, 387–392.
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