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[en] One of the most powerful forms of time domain spectroscopy is Fourier transform spectroscopy, pioneered by Pierre Jacquinot. Fourier transform spectroscopy has been widely applied, and it provides the basis of methods used to study Rydberg atoms in the time domain. While results obtained in the time and frequency domains are equivalent, it is often useful to think about a problem in both domains, and the application of time domain spectroscopy to Rydberg atoms has led to many new insights
[en] A method is presented for using a Fourier transform spectrometer (FTS) to calibrate the metrology of a second FTS. This technique is particularly useful when the second FTS is inside a cryostat or otherwise inaccessible
[en] A fully mechanized method to determine benzene in motor gasolines has been developed based on the use of Fourier transform infrared spectroscopy (FT-IR) and multicommutation. The flow network comprised a set of three-way solenoid valves and was controlled by means of a microcomputer furnished with an electronic interface and running by a software written in QUICK BASIC 4.5. The flow network and control software were designed to implement the multicommutation approach providing facilities to handle sample and reagent solutions, so that, sample dilution, external calibration and standard addition could be easily performed on-line. The method permits the direct determination of benzene without any pre-treatment of samples, with a limit of detection of 0.004% (v/v) and a variation coefficient of 1.2% (for 10 independent analysis of a gasoline sample containing 3% (v/v) benzene). Advantageous features of the method were a linear response ranging until to 3.75% (v/v), a solvent consumption of 1.2 ml per determination and an analytical throughput of 81 samples per hour. So, the described method is a fast and sustainable alternative to the previous methods for benzene determination in gasolines
[en] At Imperial College we designed and built a ultraviolet Fourier transform spectrometer with a resolution of 0.025 cm-1 (resolving power 2 x 106 at 200 nm) capable of working down to the silica transmission limit (175 nm) to obtain accurate measurements of line profiles, hyperfine structure, rotational structure of molecules, etc. Wavenumber measurements are reproducible to 0.001 cm-1. I have used the instrument at slightly lower resolution (∼500000) to explore its potential in conjunction with an coupled plasma source for analytical measurements. Its advantages and disadvantages in this respect are discussed. (author)
[en] The motivation for using a zero-dispersion monochromator as a band-pass filter with a Fourier transform spectrometer is discussed, and the design of such an instrument is presented. Benefits in performance over commercial band-pass filters are demonstrated. In addition the advantages of using the second optical output of the spectrometer are discussed, particularly with respect to absorption spectroscopy when the signal from the second output can compensate for fluctuations and drift in the intensity of the background continuum source.
[en] Infrared absorption spectra of NH3 have been obtained at high resolution (0.02 cm−1) at seven temperatures between 296 and 973 K. The spectra were recorded using a Bruker IFS 125 infrared Fourier transform spectrometer in the 2400–5500 cm−1 region and empirical lower state energies have been obtained by comparison of line strengths at different temperatures. Using two reference line lists, quantum number assignments have been made for each temperature for between 1660 and 3020 transitions, with J up to 22. The line lists obtained provide accurate line positions as well as intensities and experimental lower state energies at temperatures relevant for modeling the atmospheres of brown dwarfs and exoplanets. - Highlights: • Fourier transform infrared absorption spectra of hot ammonia. • Line positions, empirical lower state energies and intensities measured. • Line lists for brown dwarf and exoplanet atmospheres.
[en] We demonstrate a method of combining a supercontinuum light source with a commercial Fourier transform spectrometer, using a novel approach to dual-beam balanced detection, implemented with phase-sensitive detection on a single light detector. A 40 dB reduction in the relative intensity noise is achieved for broadband light, analogous to conventional balanced detection methods using two matched photodetectors. Unlike conventional balanced detection, however, this method exploits the time structure of the broadband source to interleave signal and reference pulse trains in the time domain, recording the broadband differential signal at the fundamental pulse repetition frequency of the supercontinuum. The method is capable of real-time correction for instability in the supercontinuum spectral structure over a broad range of wavelengths and is compatible with commercially designed spectrometers. A proof-of-principle experimental setup is demonstrated for weak absorption in the 1500-1600 nm region.
[en] The Atmospheric Chemistry Experiment Fourier Transform Spectrometer (ACE-FTS) on board Canada's SCISAT is described including the instrument and measurement technique and the utilization of results from the past decade. (author)
[en] This paper reports a novel micromachined stationary lamellar grating interferometer for Fourier transform (FT) based spectroscopy applications. The interferometer employs a set of tilted interdigitated light reflecting beams to produce an interferogram with spatially varying optical path difference (OPD) recorded by a line photodetector array. Due to the advantages including robustness and the absence of mechanical moving parts and optical beam splitters, the proposed spectrometer may be built in a relatively small volume and with moderate cost for wide-band radiation spectra measurement, fast time-resolved spectroscopy and for field use. The proposed stationary lamellar grating FT spectrometer was implemented using a silicon-on-insulator (SOI) micromachining process. The prototype spectrometer demonstrated a full width at half maximum (FWHM) spectral resolution of 2 nm at a wavelength of 532 nm and of 2.6 nm at 632.8 nm
[en] Application of Fourier transform methods in Nuclear Magnetic Resonance (NMR) studies has not only revolutionized the capabilities of NMR to study structure, dynamics and reactions of complex molecules in vitro, but has also provided an opportunity for non-invasive studies of complex biochemistry in vivo. This paper provides an insight into modern pulse NMR techniques and understanding of fundamental physical principles in designing various modern spin echo, polarization transfer and multi quantum coherence pulse sequences in high resolution NMR spectroscopy. Special reference is given to modern two dimensional techniques which have resulted in a major development in high resolution NMR spectroscopy during the last decade. (author)