Showing papers on "Fourier transform spectroscopy published in 2013"

Atmospheric absorption of terahertz radiation and water vapor continuum effects

Abstract: The water vapor continuum absorption spectrum was investigated using Fourier Transform Spectroscopy. The transmission of broadband terahertz radiation from 0.300 to 1.500 THz was recorded for multiple path lengths and relative humidity levels. The absorption coefficient as a function of frequency was determined and compared with theoretical predictions and available water vapor absorption data. The prediction code is able to separately model the different parts of atmospheric absorption for a range of experimental conditions. A variety of conditions were accurately modeled using this code including both self and foreign gas broadening for low and high water vapor pressures for many different measurement techniques. The intensity and location of the observed absorption lines were also in good agreement with spectral databases. However, there was a discrepancy between the resonant line spectrum simulation and the observed absorption spectrum in the atmospheric transmission windows caused by the continuum absorption. A small discrepancy remained even after using the best available data from the literature to account for the continuum absorption. From the experimental and resonant line simulation spectra the air-broadening continuum parameter was calculated and compared with values available in the literature.

Mid-infrared dual-comb spectroscopy with an optical parametric oscillator.

Abstract: We present the first implementation of mid-infrared dual-comb spectroscopy with an optical parametric oscillator. Methane absorption spectroscopy was demonstrated with a resolution of 0.2 cm(-1) (5 GHz) at an acquisition time of ~10.4 ms over a spectral coverage at 2900-3050 cm(-1). The average power from each individual mid-infrared comb line was ~1 μW, representing a power level much greater than typical difference-frequency-generation sources. Mid-infrared dual-comb spectroscopy opens up unique opportunities to perform broadband spectroscopic measurements with high resolution, high requisition rate, and high detection sensitivity.

3D spectral imaging with synchrotron Fourier transform infrared spectro-microtomography.

Abstract: Synchrotron-based Fourier transform infrared (FTIR) spectro-microtomography is a nondestructive, label-free imaging technique that allows chemical fingerprinting of intact, three-dimensional biological samples.

Segmented chirped-pulse Fourier transform submillimeter spectroscopy for broadband gas analysis.

Abstract: Chirped-pulse Fourier transform spectroscopy has recently been extended to millimeter wave spectroscopy as a technique for the characterization of room-temperature gas samples. Here we present a variation of this technique that significantly reduces the technical requirements on high-speed digital electronics and the data throughput, with no reduction in the broadband spectral coverage and no increase in the time required to reach a given sensitivity level. This method takes advantage of the frequency agility of arbitrary waveform generators by utilizing a series of low-bandwidth chirped excitation pulses paired in time with a series of offset single frequency local oscillators, which are used to detect the molecular free induction decay signals in a heterodyne receiver. A demonstration of this technique is presented in which a 67 GHz bandwidth spectrum of methanol (spanning from 792 to 859 GHz) is acquired in 58 μs.

Two-dimensional Fourier transform spectroscopy in the ultraviolet with sub-20 fs pump pulses and 250–720 nm supercontinuum probe

Abstract: Experimental realizations of two-dimensional (2D) electronic spectroscopy in the ultraviolet (UV) must so far contend with a limited bandwidth in both the excitation and particularly the probe frequency. The pump bandwidth is at best 1500 cm−1 (full width at half maximum) at a fixed wavelength of 267 nm or 400 cm−1 for tunable pulses. The use of a replica of the pump pulse as a probe limits the observation of photochemical processes to the excitation region and makes the disentanglement of overlapping signal contributions difficult. We show that 2D Fourier transform spectroscopy can be conducted in a shaper-assisted collinear setup comprising fully tunable UV pulse pairs and supercontinuum probe spanning 250–720 nm. The pump pulses are broadened up to a useable spectral coverage of 2000 cm−1 (25 nm at 316 nm) by self-phase modulation in bulk CaF2 and compressed to 18 fs. By referencing the white light probe and eliminating pump stray light contributions, high signal-to-noise ratios even for weak probe intensities are achieved. Data acquisition times as short as 4 min for a selected population time allow the rapid recording of 2D spectra for photolabile biological samples even with the employed 1 kHz laser system. The potential of the setup is demonstrated on two representative molecules: pyrene and 2,2-diphenyl-5,6-benzo(2H)chromene. Well-resolved cross-peaks are observed and the excitation energy dependence of the relaxation processes is revealed.

Femtisecond single-mole infrared spectroscopy of molecular clusters.

Abstract: The sensitivity limitations of Fourier transform infrared (FTIR) spectroscopy for the detection of molecular clusters formed in rarefied gas expansions can be overcome by synchronizing intense gas pulses at a low duty cycle with rapid interferometer scans. This turns the broadband FTIR approach into a universal cluster spectroscopy tool applicable from the far (200 cm−1) to the near (8000 cm−1) IR. It nicely complements more selective and more restricted laser-based techniques and it provides a gas-phase variant of the matrix-isolation method, the main drawback being substance consumption. A survey over the capabilities, limitations and perspectives of this high-throughput nozzle approach to cluster FTIR spectroscopy is given.

Conformational relaxation of S-(+)-carvone and R-(+)-limonene studied by microwave Fourier transform spectroscopy and quantum chemical calculations

Abstract: S-(+)-carvone (C10H14O, 5-isopropenyl-2-methylcyclohex-2-en-1-one) and R-(+)-limonene (C10H16, 4-isopropenyl-1-methylcyclohexene) have been characterized in the gas phase using a Fourier transform microwave spectrometer coupled to a supersonic molecular beam. Two conformers—with the isopropenyl group in the equatorial position—have been detected for each compound and described by a set of molecular parameters including the principal rotational constants and the quartic centrifugal distortion parameters. Quantum chemical calculations indicate that a third conformer might not be observed due to relaxation processes in the jet. The gas phase results are compared with the liquid phase IR-Raman-VCD spectra.

Laser-Based Measurements for Time and Frequency Domain Applications: A Handbook

Abstract: Shedding Light on the Art of Timekeeping The great show of time and light, the curtain rises! Brief history of timekeeping. Time-frequency equivalence The parallel story of the speed of light In the end, time and light met up again. Optical atomic clocks and outline of the book Characterization and Control of Harmonic Oscillators The ideal harmonic oscillator Self-sustained oscillators The noisy oscillator Phase noise Phase noise modeling Noise reduction in oscillators Phase noise measurements Amplitude noise measurements Passive Resonators Microwave cavities Basic properties of bulk optical cavities Cavity design considerations Ultrastable cavities Fiber cavities Whispering gallery mode resonators Continuous-Wave Coherent Radiation Sources Principles of masers Compendium of laser theory Frequency pulling Achieving single-mode oscillation The laser output Laser frequency fluctuations and stabilization techniques Intensity fluctuations Some specific laser systems High-Resolution Spectroscopic Frequency Measurements Interferometric wavelength measurements Spectroscopic frequency measurements Frequency modulation spectroscopy Magnetic rotation spectroscopy Cavity-enhanced spectroscopy Doppler-free saturation spectroscopy Doppler-free polarization spectroscopy Doppler-free two-photon spectroscopy Second-order Doppler-free spectroscopy Sub-Doppler spectroscopy in atomic/molecular beams Ramsey fringes Laser frequency standards using thermal quantum absorbers Fourier transform spectroscopy Raman spectroscopy Time and Frequency Measurements with Pulsed Laser Systems Introduction Theory of mode-locking Mode-locking mechanisms and dispersion compensation schemes Optical frequency comb synthesis from mode-locked lasers Extension of OFCSs into novel spectral regions Frequency Standards General features of frequency standards and clocks Quartz oscillators Cryogenic sapphire oscillators Photonic microwave oscillators based on WGM resonators Generation of ultrastable microwaves via optical frequency division Trapping and cooling of neutral atoms Cold stable molecules Trapping and cooling of ions Microwave atomic standards Time transfer and frequency dissemination Future Trends in Fundamental Physics and Applications Optical atomic clocks The hydrogen atom as an inexhaustible wellspring of advances in precision spectroscopy Spectroscopy of cold, trapped metastable helium Measurements of fundamental constants Constancy of fundamental constants Tests of fundamental physics laws Perspectives for precision spectroscopy of cold molecules Tests of general relativity: from ground-based experiments to space missions Quantum-enhanced time and frequency measurements Environmental metrology Bibliography

Accelerated 2D-IR Using Compressed Sensing

Abstract: A fundamental aspect of Fourier transform (FT) spectroscopy is the inverse relationship between frequency resolution and the maximum scanned time delay. In situations where essential chemical information is contained in spectral peak amplitudes rather than in their detailed shapes, it is possible to dramatically reduce the experimental acquisition time of time domain methods such as two-dimensional infrared (2D-IR) spectroscopy. By introducing compressed sensing to the analysis and experimental design of 2D-IR spectroscopy, we show that waiting-time-dependent 2D peak amplitudes reproduce conventional FT acquisition and analysis but can be recorded in a fraction of the time. Peak amplitude data are often sufficient for measuring intramolecular vibrational redistribution, vibrational coherence, chemical exchange, population, and orientational relaxation, as well as spectral diffusion.

A new, low temperature long-pass cell for mid-infrared to terahertz spectroscopy and synchrotron radiation use.

Abstract: A new cell has been designed for accurate spectroscopic measurements in the 80-400 K temperature range with variable path lengths from 3 to more than 141 m. The spectral coverage at these temperatures ranges from the visible to less than 10 cm(-1), thanks to the use of diamond windows. The design of the cryostat and vacuum setups allows vibration-free operation. The equipment provides temperature homogeneity and pressure control to better than 2% over the 100-400 K and the 0.1-1000 mbar ranges. Remote-controlled opto-mechanical systems enable in situ adjustments as well as changes of the optical path length within half an hour, in order to optimize measurement time in an open user facility. It allows then to meet the specific requirements of high resolution measurements on the Far-Infrared AILES beamline at SOLEIL as well at the LISA facility, in Creteil, in the mid-IR. This new instrument opens up the way for many experiments in the field of high-resolution gas-phase IR spectroscopy, in particular, in quantitative spectroscopy for atmospheric applications: measurements of absorption line parameters (absolute intensities, cross sections, and pressure-induced widths) using Fourier transform spectroscopy. The design and performance of the equipment are briefly presented and illustrated on spectroscopic examples.

Fourier transform imaging spectropolarimeter using simultaneous polarization modulation.

Abstract: We introduce a Fourier transform imaging spectropolarimeter composed of a simultaneous polarization modulator and a Fourier transform spectrometer without slit. The spectropolarimeter enables the generation of four sets of fringe patterns with different polarization states of light from an object point. Fourier transform of the fringe patterns provides four equations of Stokes parameters in various wavenumbers. And we can obtain the full-stokes vector from the equations. The most significant advantage of the method is that the four polarized fringe patterns are obtained simultaneously and separated without aliasing. Additionally, the advantages of the Fourier transform spectrometer are maintained, such as high radiative throughput.

High sensitivity Cavity Ring Down spectroscopy of 18O enriched carbon dioxide between 5850 and 7000 cm−1: I. Analysis and theoretical modeling of the 16O12C18O spectrum

Abstract: The room temperature absorption spectrum of highly 18O enriched carbon dioxide has been recorded by very high sensitivity CW-Cavity Ring Down spectroscopy between 5851 and 6990 cm−1 (1.71–1.43 μm). The achieved sensitivity (noise equivalent absorption αmin∼5×10−10−5×10–11 cm−1) has allowed the detection of more than 19,000 transitions belonging to eleven isotopologues of carbon dioxide. This first report is devoted to the analysis of the 16O12C18O data. A total of 6452 transitions belonging to 71 bands were rovibrationnally assigned on the basis of the predictions of the effective Hamiltonian model. For comparison, only twelve 16O12C18O bands were previously measured by Fourier Transform spectroscopy in the region. Line intensities of the weakest transitions are on the order of 2×10–29 cm/molecule. The studied spectral region is formed by ΔP =8, 9 and 10 series of transitions, where P=2V1+V2+3V3P=2V1+V2+3V3 is the polyad number (Vi are vibrational quantum numbers). The band-by-band analysis has allowed deriving accurate spectroscopic parameters of 69 bands from a fit of the measured line positions. A few resonance perturbations were identified. In particular, the 31112 (P=10) and 51105 (P=11) states belonging to different polyads are anharmonically coupled. The resulting intensity transfer leads to the observation of several extra lines of the 51105-01101 hot band which could be assigned. A major result of the present work is the measurement of the ΔP=8 bands of 16O12C18O near 5900 cm−1 which are the main responsible of the absorption of carbon dioxide in natural isotopic abundance in the region but are absent in the current version of the CO2 spectroscopic databases (HITRAN, GEISA, and CDSD). These ΔP=8 bands may significantly impact the transmission of CO2 in the 1.70 µm transparency window of importance for Venus spectra. Using the large set of newly measured line positions and those collected from the literature, the global modeling of the 16O12C18O line positions within the effective Hamiltonian approach has been performed and a new set of Hamiltonian parameters has been obtained. Using a similar approach, the global fits of the obtained intensity values of the ΔP=8, 9 and 10 series of transitions were used to derive the corresponding set of effective dipole moment parameters. The obtained results will help to improve importantly the quality of the 16O12C18O line positions and line intensities in the most currently used spectroscopic databases of carbon dioxide.

Optical biosensing of bacteria and cells using porous silicon based, photonic lamellar gratings

Abstract: We report on a method to extend the optical sensing capabilities of conventional RIFTS (reflective interferometric Fourier transform spectroscopy) biosensors for real-time detection of large microorganisms, such as bacteria and cells. Using macro porous silicon based 2D arrays of phase (lamellar) grating, we demonstrate that the zero-order optical reflectivity exhibits a similar interference pattern to that obtained for ordinary RIFTS biosensors, which can be Fourier transformed into optical thickness and exploited for biosensing. The sensing capabilities are demonstrated for Escherichia coli bacteria that were captured inside the macro-pores. The entrapment process is monitored and verified by confocal laser scanning microscopy.

Fourier transform spectroscopy around 3 microns with a broad difference frequency comb

Abstract: We characterize a new mid-infrared frequency comb generator based on difference frequency generation around 3.2 microns. High power per comb mode (>10-7 W/mode) is obtained over a broad spectral span (>700 nm). The source is used for direct absorption spectroscopy with a Michelson-based Fourier transform interferometer.

Absorption Mode Fourier Transform Electrostatic Linear Ion Trap Mass Spectrometry

Abstract: In Fourier transform mass spectrometry, it is well-known that plotting the spectrum in absorption mode rather than magnitude mode has several advantages. However, magnitude spectra remain commonplace due to difficulties associated with determining the phase of each frequency at the onset of data acquisition, which is required for generating absorption spectra. The phasing problem for electrostatic traps is much simpler than for Fourier transform ion cyclotron resonance (FTICR) instruments, which greatly simplifies the generation of absorption spectra. Here, we present a simple method for generating absorption spectra from a Fourier transform electrostatic linear ion trap mass spectrometer. The method involves time shifting the data prior to Fourier transformation in order to synchronize the onset of data acquisition with the moment of ion acceleration into the electrostatic trap. Under these conditions, the initial phase of each frequency at the onset of data acquisition is zero. We demonstrate that absorption mode provides a 1.7-fold increase in resolution (full width at half maximum, fwhm) as well as reduced peak tailing. We also discuss methodology that may be applied to unsynchronized data in order to determine the time shift required to generate an absorption spectrum.

Novel high-temperature and pressure-compatible ultrasonic levitator apparatus coupled to Raman and Fourier transform infrared spectrometers

Abstract: We describe an original apparatus comprising of an acoustic levitator enclosed within a pressure-compatible process chamber. To characterize any chemical and physical modifications of the levitated particle, the chamber is interfaced to complimentary, high-sensitivity Raman (4390–170 cm−1), and Fourier transform infrared (FTIR) (10 000–500 cm−1) spectroscopic probes. The temperature of the levitated particle can be accurately controlled by heating using a carbon dioxide laser emitting at 10.6 μm. The advantages of levitating a small particle combined with the two spectroscopic probes, process chamber, and infrared laser heating makes novel experiments possible relevant to the fields of, for example, planetary science, astrobiology, and combustion chemistry. We demonstrate that this apparatus is well suited to study the dehydration of a variety of particles including minerals and biological samples; and offers the possibility of investigating combustion processes involving micrometer-sized particles such as graphite. Furthermore, we show that the FTIR spectrometer enables the study of chemical reactions on the surfaces of porous samples and scientifically and technologically relevant, micrometer-thick levitated sheets. The FTIR spectrometer can also be used to investigate non-resonant and resonant scattering from small, irregularly-shaped particles across the mid-infrared range from 2.5 μm to 25 μm, which is relevant to scattering from interplanetary dust and biological, micrometer-sized samples but cannot be accurately modelled using Mie theory.

The Effect of Ba/Sr Ratio on Electrical and Optical Properties of BaxSr(1-x)TiO3 (x = 0.25; 0.35; 0.45; 0.55) Thin Film Semiconductor

Abstract: Ferroelectric BaxSr(1-x)TiO3 thin film semiconductors with Ba/Sr ratio deposited on silicon using chemical solution deposition (CSD) method have been investigated, followed by annealing at 850°C for 15 hours. Observations by I-V meter, LCR meter, and oscilloscope were employed to characterize the electrical properties of the thin films and the observation of fourier transform spectroscopy (FTIR) and particle size analyzer (PSA) to characterize the optical properties. The results showed that the dielectric constant was given around 2–18. Moreover the obtained films were found to be resistor because the I-V graph of each sample was ohmic either in dark or bright environment. The increase of BST mol fraction at dark environment is proportional to the increase of the curve slope. While at bright environment gives the highest curve slope for BST with fraction x = 0.45. Based on electrical conductivity of thin films, we conclude that the thin films are semiconductor. Moreover, functional group and particle size...

Detector and dispersive delay calibration issues in broadband 2D electronic spectroscopy

Abstract: Precision of two-dimensional (2D) electronic spectroscopy can be affected by imprecise calibration of the optical spectrometer and coherence time delay line. This would result in 2D spectral line shapes with twisted phase, where absorptive and dispersive parts of the signal are mixed and unrecoverable. We demonstrate two efficient and easily implementable techniques for precise spectrometer and wedge-based delay line calibration that assure acquisition of correct spectral phase in 2D spectroscopy measurements.

The X1Σg+ ground state of Mg2 studied by Fourier-transform spectroscopy

Abstract: The A1Σu+ - X1Σg+ UV spectrum of Mg2 has been investigated with high resolution Fourier-transform spectroscopy. Mg2 vapor was created in a heat pipe. Various spectroscopic methods have been employed, such as conventional absorption spectroscopy with light from a broad band lamp and laser-induced fluorescence. The high resolution of the Fourier-transform spectrometer, together with computer aided evaluation methods of the spectra, yields precise transition frequencies. The new data and data available from earlier investigations are applied in direct potential fits of lower and upper electronic states. Various representations of potential energy curves for the ground state X1Σg+ have been employed and their benefits in terms of smallest number of parameters are discussed. Scattering lengths are derived for the homonuclear isotopologues and compared with previous results.

Measurements of 12C16O2 line parameters in the 8790–8860, 9340–9650 and 11,430–11,505 cm−1 wavenumber regions by means of Fourier transform spectroscopy

Abstract: Absorption spectra of carbon dioxide, 12C16O2, have been studied in the three wavenumber ranges (8790–8860, 9340–9650 and 11,430–11,505 cm−1) of the near infrared region using spectrophotometric complex of V.E. Zuev Institute of Atmospheric Optics based on an Bruker IFS 125 HR and a 30 m multipass cell with the White type optical system. The spectra were recorded at spectral resolution of 0.015 cm−1, path length of 613.82 m and at pressure range from 209 to 400 mbar. The multispectrum fittings with the Voigt profile were performed to retrieve the line positions and intensities of eight bands 5001r−00001 (r=3, 4), 2003r−00001 (r=1,2,3) 2113r−01101 (r=1,2) and 00051−00001. The uncertainty of the line position determination is estimated to be about 0.001 cm−1. The absolute accuracy of the line intensity measurement is 5% for 5001r−00001 (r=3,4) bands, 3% for 2003r−00001 (r=1,2,3) bands, 10% for 00051−00001 band and 15% for 2113r−01101 (r=1,2) bands. The measured line intensities were used to fit the effective dipole moment parameters of 12C16O2. The fitted parameters reproduce the measured line intensities within their experimental uncertainties. A comparison of measured positions and intensities with those contained in HITRAN, CDSD, AMES-296, and High-T databases is presented and discussed.

Non-bonding interactions and internal dynamics in CH2F2⋯H2CO: a rotational and model calculations study

Abstract: The rotational spectra of three isotopologues of the 1 : 1 complex between difluoromethane and formaldehyde have been observed and assigned using pulsed jet Fourier transform microwave spectroscopy. The formaldehyde lies in the FCF plane of difluoromethane, linked through a C–H⋯F and a bifurcated CH2⋯O weak hydrogen bonds. The rotational transitions are split into two component lines with a relative intensity ratio of 1 : 3, due to the internal rotation of the formaldehyde moiety along its symmetry axis. The barrier to this motion has been estimated by using a flexible model to be V2 = 180(10) cm−1.

High-sensitive Fourier-transform spectroscopy with short-base multipass absorption cells

Abstract: A high-sensitive spectrometer operating in the range 20000–9000 cm−1 with an absorption sensitivity of 1 × 10−8 cm−1 and a spectral resolution of 0.05 cm−1, based on the Bruker IFS-125M Fourier spectrometer with a short multipass cell, is described. The high sensitivity of the spectrometer was gained through the use of the multipass absorption cell (a base length of 60 cm) with a high transmission (the ratio of the collecting mirror diameter to the base length is 1 : 4) and a high intensity light source.

Particle beam experiments for the analysis of reactive sputtering processes in metals and polymer surfaces.

Abstract: A beam experiment is presented to study heterogeneous reactions relevant to plasma-surface interactions in reactive sputtering applications Atom and ion sources are focused onto the sample to expose it to quantified beams of oxygen, nitrogen, hydrogen, noble gas ions, and metal vapor The heterogeneous surface processes are monitored in situ by means of a quartz crystal microbalance and Fourier transform infrared spectroscopy Two examples illustrate the capabilities of the particle beam setup: oxidation and nitriding of aluminum as a model of target poisoning during reactive magnetron sputtering, and plasma pre-treatment of polymers (PET, PP)

Degradation study of dye-sensitized solar cells by electrochemical impedance and FTIR spectroscopy

Abstract: Degradation in the performance of TiO2 based dye sensitized solar cells was studied by electrochemical impedance (EIS) and Fourier transform infrared (FTIR) spectroscopy Degradation was carried out by aging the dye-sensitized solar cells in ambient conditions for 4500 hours The current-voltage performance results, measured under solar simulator light show a 88% reduction in the short circuit current and 89% reduction in efficiency Significant increase in the electron transfer resistance at TiO2/dye/electrolyte interfaces supports the fact that dye degradation and detachment from TiO2 surface governs the degradation process in DSSCs FTIR analysis determines the cause of degradation in the DSSC performance to be the detachment of the dye molecules from the TiO2 surface promoted by the adsorption of H2O from the ambient This was observed as an increase in the H2O absorption band between 3000 - 3600 cm-1, a decrease in the absorption band of SCN at 2100 cm-1, and TBA+ at 2974, 2929, and 2872 cm-1 The present work highlights the advantage of coupling electrochemical impedance and FTIR spectroscopy to evaluate changes in cell performance and to determine the cause of degradation on a molecular level