Fourier Transform Interferometer Research Articles

Design, Operation, and Characterization of a Laboratory Spatial-Spectral Fourier Transform Interferometer

Design, Operation, and Characterization of a Laboratory Spatial-Spectral Fourier Transform Interferometer

Improved centrifugal and hyperfine analysis of ND2H and NH2D and its application to the spectral line survey of L1544

Quantifying molecular abundances of astrochemical species is a key step towards the understanding of the chemistry occurring in the interstellar medium. This process requires a profound knowledge of the molecular energy levels, including their structure resulting from weak interactions between nuclear spins and the molecular rotation. With the aim of increasing the quality of spectral line catalogs for the singly- and doubly-deuterated ammonia (NH2D and ND2H), we have revised their rotational spectra by observing many hyperfine-resolved lines and more accurate high-frequency transitions. The measurements have been performed in the submillimeter-wave region (265–1565 GHz) using a frequency modulation submillimeter spectrometer and in the far-infrared domain (45–220 cm−1) with a synchrotron-based Fourier-transform interferometer. The analysis of the new data, with the interpretation of the hyperfine structure supported by state-of-the-art quantum-chemical calculations, led to an overall improvement of all spectroscopic parameters. Moreover, the effect of the inclusion of deuterium splittings in the analysis of astrophysical NH2D emissions at millimeter wavelengths has been tested using recent observations of the starless core L1544, an ideal astrophysical laboratory for the study of deuterated species. Our results show that accounting for hyperfine interactions leads to a small but significant change in the physical parameters used to model NH2D line emissions.

A rotational and vibrational investigation of phenylpropiolonitrile (C6H5C3N)

The evidence for benzonitrile (C6H5CN) in the starless cloud core TMC–1 makes high-resolution studies of other aromatic nitriles and their ring-chain derivatives especially timely. One such species is phenylpropiolonitrile (3-phenyl-2-propynenitrile, C6H5C3N), whose spectroscopic characterization is reported here for the first time. The low resolution (0.5 cm−1) vibrational spectrum of C6H5C3N has been recorded at far- and mid-infrared wavelengths (50–3500 cm−1) using a Fourier Transform interferometer, allowing for the assignment of band centers of 14 fundamental vibrational bands. The pure rotational spectrum of the species has been investigated using a chirped-pulse Fourier transform microwave (FTMW) spectrometer (6– 18 GHz), a cavity enhanced FTMW instrument (6–20 GHz), and a millimeter-wave one (75–100 GHz, 141–214 GHz). Through the assignment of more than 6200 lines, accurate ground state spectroscopic constants (rotational, centrifugal distortion up to octics, and nuclear quadrupole hyperfine constants) have been derived from our measurements, with a plausible prediction of the weaker lines through calculations. Interstellar searches for this highly polar species can now be undertaken with confidence since the astronomically most interesting radio lines have either been measured or can be calculated to very high accuracy below 300 GHz.

Archaeometric studies in pre-colonial guarani ceramic production (Taquari, Brazil)

ABSTRACT The archeological site RS-TQ-141 is located in Rio Grande do Sul (Brazil) and belongs to the pre-colonial Guarani Tradition (between fifth and seventeenth century). The site extends to the bank of the Taquari River. About 200 small fragments of ceramic from the site present internal and/or external coating surfaces. Archaeometry analyses were applied in order to understand coating application mechanism. X-ray Fluorescence (XFR) analyses revealed that the main elements are iron, titanium, potassium, and calcium. Applying the micro Fourier Transform Interferometer (ATR-FTIR) method it was possible to differentiate white and red coatings produced with different types of (ocher) clays. ATR-FTIR was applied in order to try to distinguish the vessels use. The coatings were produced with the same groups of clays used for the manufacture of ceramics. The presence of at least two groups of clay is recorded: montmorillonite-like and kaolinite-like. The white coatings can be distinguished in the FTIR spectra by the presence of a carbonate peak. From this research, there does not seem to be any difference between internal and external coatings. Carbonyl materials were detected, both in the coating and in the production of the ceramics; the latter is probably related to pyrolysis.

Evidence of microplastics from benthic jellyfish (Cassiopea xamachana) in Florida estuaries

Plastic pollution is a concern in many nearshore ecosystems, and it is critical to understand how microplastics (plastics <5 mm in length) affect nearshore marine biota. Here, we report the presence of microplastics in the benthic, upside-down jellyfish (Cassiopea xamachana) across three estuaries in south Florida. Microplastics were recovered from Cassiopea using an acid digestion, then enumerated via microscopy, and identified using micro Fourier-transform interferometer (μFTIR) analysis. Out of 115 specimens analyzed, 77% contained microplastics. Bell diameter and number of plastics per individual varied significantly across locations with the highest plastic densities and bell diameter observed in individuals from Big Pine Key, followed by Jupiter, and Sarasota. μFTIR analysis confirmed that synthetic microfibers were the dominant microplastic measured at all three locations and may indicate Cassiopea as potential sinks of microplastic. Cassiopea may be used as bioindicators of microplastic contamination in the future, allowing for potential plastic pollution mitigation.

Infrared Spectroscopic and Kinetic Characterization on the Photolysis of Nitrite in Alcohol-Containing Aqueous Solutions.

Nitrite is regarded as a potential OH and NO precursor in aqueous solution upon ultraviolet photolysis. A step-scan Fourier-transform interferometer was employed to collect the transient infrared difference spectra upon excitation of the sodium nitrite aqueous solution in the presence of methanol and ethanol upon 355 nm pulsed excitation. The photolytic intermediates were proposed to be NO and NO2 via the direct dissociation from NO2- and the rapid reaction of OH and NO2-, respectively. Coupled with the theoretical calculations of the absolute energies and harmonic wavenumbers of relevant species using B3LYP density functional theory with the C-PCM model to account for the medium effect of H2O, a transient band at 1860-2030 cm-1 could be attributed to dissolved N2O3 isomers that could be quickly generated from NO + NO2. On the basis of the predicted thermodynamics, the reactions of alcohols with N2O3 were less thermodynamically favorable than that of water, resulting in a slightly decelerated depletion rate of N2O3 in alcohol-containing aqueous solution. Comparing the transient population of N2O3 in the absence and presence of CH3OH or C2H5OH, the upper-bound bimolecular rate coefficient of NO or NO2 with alcohols is reported as 7.3 × 103 M-1 s-1 for the first time. The spectroscopic and kinetic evidence of the reactivity of alcohols with NO, NO2, and N2O3 are provided to augment the roles of alcohols and NxOy in solution or in aqueous aerosol photochemistry.

The KISS Experiment

Mapping millimetre continuum emission has become a key issue in modern multi-wavelength astrophysics. In particular, spectrum-imaging at low frequency resolution is an asset for characterizing the clusters of galaxies via the Sunyaev Zeldovich (SZ) effect. In this context, we have built a ground-based spectrum-imager named KIDs Interferometer Spectrum Survey (KISS). This instrument is based on two 316-pixel arrays of Kinetic Inductance Detectors (KID) cooled to 150 mK by a custom dilution refrigerator-based cryostat. By using Ti-Al and Al absorbers, we can cover a wide frequency range between 80 and 300 GHz. In order to preserve a large instantaneous Field of View (FoV) 1 degree the spectrometer is based on a Fourier Transform interferometer. This represents a technological challenge due to the fast scanning speed that is needed to overcome the effects of background atmospheric fluctuations. KISS is installed at the QUIJOTE 2.25 m telescope in Tenerife since February 2019 and is currently in its commissioning phase. In this proceeding we present an overview of the instrument and the latest results.

Technique for Inverting Transmission Spectra to Measure Freon Concentration

We propose an approach to selecting the optimal parameters for solving the inverse problem for determining the total freon content (TC) from ground-based spectrometric measurements of solar radiation. The approach was developed for measurements at the St. Petersburg NDACC station using a Bruker FS125HR Fourier-transform interferometer and implemented as applied to measurements of the total content of the hydrochlorofluorocarbon R-22 (HCF2Cl). Based on the optimal set of parameters obtained, we retrieved the total R-22 content above the St. Petersburg station in the period 2009–2018 and obtained estimates of the measurement uncertainties: average systematic uncertainty 4.8%, random uncertainty 3.7% over the entire observational period. A preliminary estimate of the trend is 2.64 ± 0.22% per year.

Discovery of New Coronal Lines at 2.843 and 2.853 μm

Abstract Two new emission features were observed during the 2017 August 21 total solar eclipse by a novel spectrometer, the Airborne Infrared Spectrometer (AIR-Spec), flown at 14.3 km altitude aboard the NCAR Gulfstream-V aircraft. We derive wavelengths in air of 2.8427 ± 0.00009 μm and 2.8529 ± 0.00008 μm. One of these lines belongs to the transition in Ar-like Fe ix. This appears to be the first detection of this transition from any source. Minimization of residual wavelength differences using both measured wavelengths, together with National Institute of Standards and Technology (NIST) extreme ultraviolet wavelengths, does not clearly favor assignment to Fe ix. However, the shorter wavelength line appears more consistent with other observed features formed at similar temperatures to Fe ix. The transition occurs between two levels within the excited configuration, 429,000 cm−1 above the ground level. The line is therefore absent in photo-ionized coronal-line astrophysical sources such as the Circinus Galaxy. Data from a Fourier transform interferometer (FTIR) deployed from Wyoming show that both lines are significantly attenuated by telluric H2O, even at dry sites. We have been unable to identify the longer wavelength transition.

Re-analysis of the (100), (001), and (020) rotational structure of SO2 on the basis of high resolution FTIR spectra

Three infrared spectra, weak (W), medium (M), and strong (S), of the 32SO2 molecule were recorded with high resolution in the 1000–1500cm−1 region. Spectra were recorded with the Fourier Transform interferometer Bruker IFS-120 HR in Oulu (Finland) with different pressures, absorption path lengths, and recording time. That allowed us to record not only the ν1 and ν3 bands with higher values of quantum numbers J and Ka than it was made earlier, but to record for the first time very weak 2ν2 band. In this case, transitions with the values Jmax./Kamax. equal to 89/37, 109/28, and 54/9 were assigned in the experimental spectra for the bands ν1, ν3, and 2ν2, respectively. As it became clear in the course of the analysis, the rotational parameters of the ground vibrational state, known in the literature, do not describe suitably the ground state combination differences (GSCD) for the states with the value Ka>26–27. As a consequence, the ground state rotational parameters were improved on the basis of our experimental data. The 12131 transitions assigned in the experimental spectrum (7618, 3952, and 561 transitions of the bands ν1, ν3, and 2ν2, respectively) were used for determination of ro-vibrational energy values of the vibrational states (100), (001), and (020). The lasts were used then in the fit procedure together with known in the literature high accurate sub-millimeter wave data. Resonance interactions between all three vibrational states have been taken into account in the Hamiltonian used for the fit. As a result, the 51 varied parameters, obtained from the fit, reproduce 4063 ro-vibrational energies of the states (100), (001), and (020) (12131 initial experimental transitions) with accuracies close to experimental uncertainties: the rms deviation is 6.1×10−5cm−1, 9.7×10−5cm−1, and 13.9×10−5cm−1 for our FTIR data (for the (100), (001), and (020) states, respectively), and comparable with experimental uncertainties for heterodyne data.

Investigation of atmospheric $$ {\text{O}}_{2}{\text{X}}{^{ 3}}{ \sum_{\text{g}}^{ - }} \,{\text{to}}\, {\text{b}}{^{ 1}}{ \sum_{\text{g}}^{ + }} $$ using open-path tunable diode laser absorption spectroscopy

A tunable diode laser absorption spectroscopy (TDLAS) device fiber coupled to a pair of 12.5 in. telescopes was used to study atmospheric propagation for open path lengths of 100–1,000 meters. More than 50 rotational lines in the molecular oxygen A-band O2\( {\text{X}}{^{ 3}}{ \sum_{\text{g}}^{ - }} \,{\text{to}}\, {\text{b}}{^{ 1}}{ \sum_{\text{g}}^{ + }} \) transition near 760 nm were observed. Temperatures were determined from the Boltzmann rotational distribution to within 1.3 % (less than ±2 K). Oxygen concentration was obtained from the integrated spectral area of the absorption features to within 1.6 % (less than ±0.04 × 1018 molecules/cm3). Pressure was determined independently from the pressure-broadened Voigt lineshapes to within 10 %. A fourier transform interferometer (FTIR) was also used to observe the absorption spectra at 1 cm−1 resolution. The TDLAS approach achieves a minimum observable absorbance of 0.2 %, whereas the FTIR instrument is almost 20 times less sensitive. Applications include atmospheric characterization for high energy laser propagation and validation of monocular passive raging.

Far infrared Fourier-transform spectroscopy of mono-deuterated hydrogen peroxide HOOD

We present the gas phase spectrum of singly deuterated hydrogen peroxide, HOOD, in its vibrational ground state, recorded by the high resolution Fourier-transform interferometer located at the AILES synchrotron beamline connected to SOLEIL. More than 1000 transitions in the range from 20 to 143cm−1 were assigned, leading to a set of preliminary rotational and centrifugal distortion constants determined by least squares fit analysis. All transitions are split by the tunneling motion of a hindered internal rotation. The splitting has been determined to be 5.786(13)cm−1 in the torsional ground state and it shows a dependence on the rotational quantum number Ka. Some perturbations were not treated yet, but the present analysis permits to obtain a preliminary set of parameters.

Study On Spectrometer Dynamic-mirror Precision Drive System

The spectrometer dynamic-mirror precision drive system is the important component of Fourier Transform Interferometer. In the view of the requirement of the spectrum sampling, the dynamic-mirror drive system designed by this paper should provide the accurate interval signal for spectrum sampling as well as the dynamic-mirror-zero signal for starting sampling point. In order to achieve this goal, this paper uses the grating ruler and grating-zero reference as the control sensors to generate the needed interval signal and dynamic-mirror-zero signal through the intelligent control strategy based on AT89C2051. The Experiments show that the dynamic-mirror drive system designed by this paper well meet the demand of Fourier Transform Interferometer for spectrum sampling.

Slow-Light Fourier Transform Interferometer

We describe a new type of Fourier transform (FT) interferometer in which the tunable optical delay between the two arms is realized by using a continuously variable slow-light medium instead of a moving arm as in a conventional setup. The spectral resolution of such a FT interferometer exceeds that of a conventional setup of comparable size by a factor equal to the maximum group index of the slow-light medium. The scheme is experimentally demonstrated by using a rubidium atomic vapor cell as the tunable slow-light medium, and the spectral resolution is enhanced by a factor of approximately 100.

Global fit of the high-resolution infrared spectrum of D 2S

High-resolution Fourier-transform spectra of the D 2S molecule in the regions of polyads of interacting vibrational states v = 3/2, 2, 5/2, 3 and 7/2 ( v = v 1 + v 2/2 + v 3) were recorded for the first time with a Bruker IFS 120 Fourier-transform interferometer and analysed. A global fit of all currently available rotation–vibration energies has been made for 22 vibrational states of the D 2S molecule. The resulting set of 231 parameters reproduces all the initial experimental data (about 3670 vibration–rotation energies which correspond to more than 9700 ro-vibrational transitions with J max = 25) with accuracies close to the experimental uncertainties.

High-resolution ro-vibrational spectroscopy of HDO in the region of 8900–9600 cm −1

The high-resolution absorption spectrum of the HDO molecule was recorded with a Fourier-transform interferometer in the region of 8900–9600 cm −1, where the strongly interacted bands 2 ν 1 + ν 3, 3 ν 1 + ν 2, ν 1 + 2 ν 2 + ν 3, 2 ν 1 + 3 ν 2, 4 ν 2 + ν 3, ν 1 + 5 ν 2, and 7 ν 2 are located. About 1000 transitions were assigned to these seven bands based on the ab initio predictions [J. Chem. Phys. 106 (1997) 4618]. Altogether, 375 upper energy levels were determined, including 24 energy levels of the highly excited bending (070) state. On that basis, the necessity of the “Effective Hamiltonian” concept in the spectroscopic analysis is discussed.

Electrical and Radiation Characteristics of Semilarge Photoconductive Terahertz Emitters

We present experimental characterization of semilarge photoconductive emitters, including their electrical/photoconductive parameters and terahertz spectra. A range of emitters were studied and fabricated on both LT-GaAs and SI-GaAs, having a variety of electrode geometries. The spatial cone of terahertz radiation was defined. The dependencies of the photocurrent and the terahertz power on the bias voltage and the laser power were determined. A Fourier-transform interferometer is used to determine the terahertz spectra and to clarify the effects of the substrate and electrode geometry.

Ground-Based Infrared Remote Sensing of Cloud Properties over the Antarctic Plateau. Part I: Cloud-Base Heights

Abstract A Fourier-transform interferometer, operated throughout 1992 at South Pole Station, measured downward spectral longwave radiance from 550 to 1500 cm−1 (7–18 μm) at a resolution of 1 cm−1. Radiance measurements were usually made twice daily, coincident with routine launches of radiosondes made by the South Pole Weather Office; 223 radiance measurements (40% of the observations) were of cloudy-sky conditions. Cloud-base heights are retrieved from these data using a ground-based version of the radiance-ratioing method, which was originally developed to retrieve cloud-top heights from satellite data. Frequencies in the R branch of the 15-μm carbon dioxide band are used, exploiting the variation of atmospheric opacity with wavenumber. The annual cycle of cloud-base heights shows a bimodal distribution in all seasons except during the brief summer (December–January). Cloud-base heights are typically higher in the summer than in winter. Although retrieved cloud-base heights are uncorrelated with heights...

Correlation of aerosol and carbon monoxide at 45°S: Evidence of biomass burning emissions

Altitude profiles of Carbon Monoxide (CO) and aerosols have been compared from the Network for Stratospheric Change (NDSC) mid‐latitude southern hemisphere site at Lauder, New Zealand. The CO mixing ratio profile was derived from infrared spectra recorded with a very high resolution Fourier Transform interferometer using three lines of the (1–0) band between 2057 and 2160 cm−1. The aerosol surface area was derived from balloon‐borne backscatter radiation at 940 nm. Both datasets show significant enhancements occurring over the observation site in the austral spring. When displayed together their combined effect illustrates the close correlation between CO and aerosols. Peak concentrations are consistently recorded between September and October over a five year time frame (1994–1999), with the enhancements typically occurring at heights of between 3 to 8 km. The temporal and spatial correlation between the aerosol plumes and enhanced CO concentrations are interpreted in terms of the effect of long range transport of biomass burning plumes in combination with the El Nino‐Southern Oscillation (ENSO) cycles influence on southern hemisphere climate dynamics.

Infrared intracavity laser absorption spectroscopy with a continuous-scan Fourier-transform interferometer

High-quality broadband infrared high-resolution spectra were obtained by use of the intracavity laser absorption spectroscopy technique with a Ti:sapphire laser in combination with a continuous-scan Fourier-transform (FT) interferometer. With electronic filtering used to smooth out the fluctuations of the laser power, the absorption of atmospheric water vapor in the range of 12,450-12,700 cm(-1) was recorded at a resolution of 0.05 cm(-1). A signal-to-noise ratio of greater than 300 was observed in this spectrum, corresponding to a minimum detectable absorption of approximately 2 x 10(-9) cm(-1). Comparison with previous measurements by use of a conventional FT technique shows that this method gives absorption spectra with highly accurate line positions along with reasonable line intensities. Investigation of the evolution of intracavity laser absorption spectra with the generation time is also shown to be possible with a continuous-scan FT spectrometer by use of the interleave rapid-scan method.