Intracavity Laser Absorption Spectroscopy Research Articles

Revisiting iron oxidation chemistry in synthesis flames: Insights from a shock-tube study with intracavity laser absorption spectroscopy tracking of FeO

The reaction between Fe atoms and O2 in a mixture of iron-pentacarbonyl (IPC, 2 ppm) and oxygen (100 ppm), diluted in argon, has been studied in a shock tube behind reflected shock waves over the temperature and pressure ranges of 1050–3400 K and 0.7–2.0 bar. Time-resolved measurements of Fe and FeO have been performed simultaneously using a combination of atomic resonance absorption spectroscopy (ARAS) and intracavity laser absorption spectroscopy (ICAS) with a custom-made broadband dye laser, respectively. For ICAS, absorption features in the spectral range from 16,316 to 16,353 cm−1 have been evaluated, and the oscillator strengths for all 41 assigned ro-vibronic transitions have been expressed. For most of the experimental cases, the measured Fe and FeO traces agreed well with the mechanism reported in this work. The quantitative and highly-sensitive measurements revealed the presence of FeO at temperatures below 1400 K, leading to a reconsideration of rate coefficients for different Fe oxidation channels.

Ultraviolet intracavity laser absorption spectroscopy

We report the first extension of Intracavity Laser Absorption Spectroscopy to the ultraviolet, made possible by a Ce-doped gain medium. The effectiveness of the technique is demonstrated by measurements on three important species in combustion and atmospheric chemistry: formaldehyde, sulfur dioxide, and hydroxyl radical.

Widely-Tunable Quantum Cascade-Based Sources for the Development of Optical Gas Sensors.

Spectroscopic techniques based on Distributed FeedBack (DFB) Quantum Cascade Lasers (QCL) provide good results for gas detection in the mid-infrared region in terms of sensibility and selectivity. The main limitation is the QCL relatively low tuning range (~10 cm−1) that prevents from monitoring complex species with broad absorption spectra in the infrared region or performing multi-gas sensing. To obtain a wider tuning range, the first solution presented in this paper consists of the use of a DFB QCL array. Tuning ranges from 1335 to 1387 cm−1 and from 2190 to 2220 cm−1 have been demonstrated. A more common technique that will be presented in a second part is to implement a Fabry–Perot QCL chip in an external-cavity (EC) system so that the laser could be tuned on its whole gain curve. The use of an EC system also allows to perform Intra-Cavity Laser Absorption Spectroscopy, where the gas sample is placed within the laser resonator. Moreover, a technique only using the QCL compliance voltage technique can be used to retrieve the spectrum of the gas inside the cavity, thus no detector outside the cavity is needed. Finally, a specific scheme using an EC coherent QCL array can be developed. All these widely-tunable Quantum Cascade-based sources can be used to demonstrate the development of optical gas sensors.

Intracavity laser spectroscopy with Fourier-transform detection of tungsten sulfide, WS: Analysis of the (1,0) band of the [13.10] Ω = 1 − X3Σ–0+ transition

The (1,0) band of the [13.10] Ω = 1 − X3Σ–0+ transition of WS has been observed and recorded at Doppler-limited resolution using intracavity laser absorption spectroscopy detected with a Fourier-transform spectrometer (ILS–FTS). The tungsten sulfide molecules were produced in the plasma discharge formed when 0.35 A of RF current were applied to a W-lined Cu hollow cathode in an atmosphere that was 0.1% CS2, ~30% H2, and ~70% Ar at a total pressure of 1 torr. The hollow cathode was located within the resonator cavity of a tunable Ti:Sapphire laser, causing molecular absorption to be superimposed upon the broadband profile of the laser. This profile was detected using a Bruker IFS 125 M spectrometer using an instrument resolution of 0.01 cm−1. The ILS-FTS spectrum was analyzed using PGOPHER. Experimental line positions from the laser induced fluorescence (LIF) spectrum of WS [Tsang et al., J. Mol. Spec., 359, 31 (2019)] were included in the fit, and a limited Dunham model was built in PGOPHER to characterize the X 3Σ–0+ ground state of WS. The rotational coverage of the ground state is expanded from 0 < J < 35 to 0 < J < 62, the uncertainty in the ground state constants for WS are reduced by a factor of three, and a potential energy curve for that state is produced from the Dunham constants using the RKR method.

Identification of two new electronic transitions of TaF using intracavity laser spectroscopy

Several bands in two new electronic transitions of TaF have been recorded in high resolution using intracavity laser absorption spectroscopy (ILS). The (1,0), (0,0), and (0,1) bands of the [16.0]0+ – X3Σ−(0+) transition and the (2,1), (1,0), (0,0), (0,1), and (1,2) bands of the [16.3]1 – X3Σ−(0+) transition were observed. TaF was produced in the plasma discharge of a tantalum-lined copper hollow cathode with Ar [1 torr] as a sputter gas and trace of SF6 as a fluoride source. Trace H2 [1%] also was used as it was found to increase the intensity of the observed transitions. The transitions were analyzed using PGOPHER, and the obtained molecular parameters are presented and compared with a previous work.

On the Search for the Electric Dipole Moment of the Electron: P-, T-Odd Faraday Effect on a PbF Molecular Beam

It has been proposed to measure the electric dipole moment of the electron on the basis of the observation of the P-, T-odd Faraday effect on a molecular beam intersecting a cavity using cavity-enhanced intracavity laser absorption spectroscopy. The effective electric field acting on the electric dipole moment of the electron, as well as the molecular parameter of the scalar-pseudoscalar nucleus-electron interaction, has been calculated for the ground and excited electronic states of the lead monofluoride molecule. The simulation of the experiment has shown that the proposed approach allows improving the current bounds on the electric dipole moment of the electron and the scalar-pseudoscalar nucleus-electron interaction constant by six orders of magnitude.

Mass-independent dunham analysis of the [7.7] Y2Σ+ – X2Πi and [16.3] A2Σ− – X2Πi transitions of copper monoxide, CuO

The electronic spectrum of CuO has been studied extensively experimentally. In his review on the spectroscopy of the 3d transition metal oxides (Merer, 1989), Anthony Merer summarized the available experimental data for CuO, which encompassed over 20 publications. There have been 4 subsequent publications on CuO that have included: high resolution Fourier-Transform emission spectroscopy (FTS) (O’Brien et al., 1996), mm- and sub-mm microwave absorption spectroscopy (Steimle et al., 1997), moderate resolution laser induced fluorescence (LIF) spectroscopy (Jin et al., 2002), and high-resolution molecular beam LIF spectroscopy, both in the presence and absence of an external electric field (Zhuang et al., 2010). Despite this extensive study, analyses of spectra have been restricted to 63CuO, even though the natural abundance of 65Cu is significant (63Cu:65Cu is 69%:31%). Additionally, the Λ-doubling parameter for the X 2Πi state of CuO is assigned a negative sign in the FTS analysis, but is assigned a positive sign in the microwave and molecular beam LIF analyses. In this study, high resolution spectra for (0,0) and (1,1) bands of the [16.3] A2Σ− – X2Πi transition of CuO have been recorded using intracavity laser absorption spectroscopy (ILS). Features due to the (0,0) band of 65CuO were clearly identified in the spectra and included in the analysis. The CuO FTS spectrum was retrieved from the archive for the McMath-Pierce Solar Observatory at Kitt Peak, and several additional vibrational bands of the [7.7] Y2Σ+ – X2Πi transition of CuO were identified in the FTS data, including the (1,0), (0,0), and (0,1) bands of 65CuO. The ILS, FTS, microwave and molecular beam LIF data were simultaneously fit to a mass-independent Dunham type Hamiltonian using PGOPHER. In total, 13,019 observations were fit to 1 constrained and 46 floated parameters. The results of this simultaneous fit show a Cu-isotope dependent shift in electronic energy for the [7.7] Y2Σ+ – X2Πi and [16.3] A2Σ− – X2Πi transitions of CuO. The results also confirm that the sign of q in the X 2Πi ground state is negative. Potential energy curves were generated from the molecular constants obtained in the fit for the [7.7] Y2Σ+ and X 2Πi states using the RKR method. These potential energy curves are significantly different and clearly indicate the Y and X state do not form a pure-precession pair.

Experimental study of the dynamics of fast gas heating in a low-pressure DC discharge in nitrogen

This paper discusses the experimental studies of the gas heating dynamics of a low-pressure DC discharge in nitrogen. The time evolution of the discharge current, the electric field, and the gas temperature in the positive column of a pulsed DC discharge in nitrogen for a gas pressure of 1.5 Torr and a current density of 0.1–6 A cm−2 were measured. The gas temperature in the discharge was equal to the rotational temperature in the and metastable electronic states of nitrogen. The rotational temperature in the state was found from the spectra of the first positive system of N2, which were recorded by using intracavity laser absorption spectroscopy. The rotational temperature in the state was determined from the VUV emission spectra of the Lyman–Birge–Hopfield system of N2. The gas temperatures obtained by these two spectroscopic methods were in good agreement. It was found that two phases with different gas heating rates exist during a discharge pulse. In the first phase, the gas heating was relatively slow. With increasing current density, the duration of the first heating phase decreased from 150 μs at 0.2 A cm−2 to 10 μs at 2.5 A cm−2. In the second phase, fast gas heating occurred. The gas heating rate in the second phase increased with increasing discharge current, and was equal to 10 K μs−1 for a current density of about 2 A cm−2. The relation between the rate of the fast heating and the density of deposited power obeyed a power law. In 300 μs, the gas was heated in the discharge up to about 400, 1500, and 3000 K for current densities of 0.2, 1, and 2.5 A cm−2, respectively. These experimental data can be the basis for verification of kinetic models for gas heating dynamics in a low-pressure discharge in nitrogen.

Concentration measurements by intracavity laser absorption spectroscopy for the case of strongly overlapped spectra

The feasibility of fiber laser intracavity absorption spectroscopy (FLICAS) for accurate measurement of pressure and concentration of CO and $$\hbox {CO}_2$$ at elevated pressures (up to 6.5 atm) was studied. FLICAS is a very sensitive absorption spectroscopy method which allows for simultaneous measurement of several species even in harsh environment, since it is not sensitive to broadband optical losses caused by particle scattering and absorption, optical window contamination, etc. However, the wings of spectral lines can overlap at elevated pressures, resulting in broadband absorption which is not monitored by FLICAS. It makes the direct evaluation of baseline challenging. Nevertheless, fitting the lineshapes of individual lines using the HITRAN database allows for recovering of the baseline position and shape in some cases. The CO and $$\hbox {CO}_2$$ spectra were studied under controlled conditions in the spectral range of 6350–6385 cm $$^{-1}$$ and processed by custom LabVIEW code to take into account the overlapping line effect. This procedure allows for accurate determination of the pressure and the CO concentration at least up to 6.5 atm. More dense and line-rich $$\hbox {CO}_2$$ spectrum allows correct pressure evaluation up to 6.5 atm, albeit with higher uncertainty. Accurate measurements of the $$\hbox {CO}_2$$ concentration are possible only up to about 4 atm.

Detection of OH in an atmospheric flame at 1.5 um using optical frequency comb spectroscopy

We report broadband detection of OH in a premixed CH4/air flat flame at atmospheric pressure using cavity-enhanced absorption spectroscopy based on an Er:fiber femtosecond laserand a Fourier transform spectrometer.By taking ratios of spectra measured at different heights above the burner we separate twenty OH transitions from the largely overlapping water background. Weretrieve from fits to the OH lines the relative variation of the OH concentration and flame temperature with height above the burner and compare them with 1-D simulations of the flamestructure. Full Text: PDF ReferencesG. Meijer, M. G. Boogaarts, R. T. Jongma, D. H. Parker and A. M. Wodtke, "Coherent cavity ring down spectroscopy", Chem. Phys. Lett. 217, 1, 112 (1994). CrossRef S. Cheskis, I. Derzy, V. A. Lozovsky, A. Kachanov and D. Romanini, "Cavity ring-down spectroscopy of OH radicals in low pressure flame", Appl. Phys. B 66, 3, 377 (1998). CrossRef X. Mercier, E. Therssen, J. F. Pauwels and P. Desgroux, "Cavity ring-down measurements of OH radical in atmospheric premixed and diffusion flames.: A comparison with laser-induced fluorescence and direct laser absorption", Chem. Phys. Lett. 299, 1, 75 (1999). CrossRef J. Scherer, D. Voelkel and D. Rakestraw, "Infrared cavity ringdown laser absorption spectroscopy (IR-CRLAS) in low pressure flames", Appl. Phys. B 64, 6, 699 (1997). CrossRef R. Peeters, G. Berden and G. Meijer, "Near-infrared cavity enhanced absorption spectroscopy of hot water and OH in an oven and in flames", Appl. Phys. B 73, 1, 65 (2001). CrossRef T. Aizawa, "Diode-laser wavelength-modulation absorption spectroscopy for quantitative in situ measurements of temperature and OH radical concentration in combustion gases", Appl. Opt. 40, 27, 4894 (2001). CrossRef B. Löhden, S. Kuznetsova, K. Sengstock, V. M. Baev, et al., "Fiber laser intracavity absorption spectroscopy for in situ multicomponent gas analysis in the atmosphere and combustion environments", Appl. Phys. B 102, 2, 331 (2011). CrossRef A. Matynia, M. Idir, J. Molet, C. Roche, et al., "Absolute OH concentration profiles measurements in high pressure counterflow flames by coupling LIF, PLIF, and absorption techniques", Appl. Phys. B 108, 2, 393 (2012). CrossRef R. S. Watt, T. Laurila, C. F. Kaminski and J. Hult, "Cavity Enhanced Spectroscopy of High-Temperature H2O in the Near-Infrared Using a Supercontinuum Light Source", Appl. Spectrosc. 63, 12, 1389 (2009). CrossRef C. Abd Alrahman, A. Khodabakhsh, F. M. Schmidt, Z. Qu and A. Foltynowicz, "Cavity-enhanced optical frequency comb spectroscopy of high-temperature H2O in a flame", Opt. Express 22, 11, 13889 (2014). CrossRef A. Foltynowicz, P. Maslowski, A. J. Fleisher, B. J. Bjork and J. Ye, "Cavity-enhanced optical frequency comb spectroscopy in the mid-infrared application to trace detection of hydrogen peroxide", Appl. Phys. B 110, 2, 163 (2013). CrossRef Z. Qu, R. Ghorbani, D. Valiev and F. M. Schmidt, "Calibration-free scanned wavelength modulation spectroscopy ? application to H2O and temperature sensing in flames", Opt. Express 23, 12, 16492 (2015). CrossRef L. Rutkowski, A. Khodabakhsh, A. C. Johansson, D. M. Valiev, et al., "Measurement of H2O and OH in a Flame by Optical Frequency Comb Spectroscopy", CLEO: Science and Innovations SW4H.8 (2016). CrossRef L. S. Rothman, I. E. Gordon, Y. Babikov, A. Barbe, et al., "The HITRAN2012 molecular spectroscopic database", J. Quant. Spectrosc. Radiat. Transf. 130, 4 (2013). CrossRef

Experimental and modelling study of 1CH2 in premixed very rich methane flames

Stoichiometric and very rich (1.5≤ɸ≤1.9) laminar flat flames of methane have been investigated using nonintrusive laser diagnostics. Premixed CH4+O2+N2 flames were stabilized at a pressure of 30±0.3Torr. Temperature profiles were obtained using laser-induced fluorescence of OH. Absolute concentration profiles of singlet methylene, 1CH2, were measured by intracavity laser absorption spectroscopy. Uncertainties of the relative and absolute concentrations of singlet methylene were evaluated to be about ±10% and ±30%, respectively. These new experimental data were compared with predictions of three detailed kinetic mechanisms: GRI-mech. 3.0, Aramco mech. 1.3, and the model under development in Lund. In the last mechanism 78 rate constants of reactions along the pathway CH3→1CH2→3CH2→CH were reviewed and updated. No adjustment or tuning of the rate expressions to accommodate experimental results was attempted. GRI-mech. significantly overpredicts singlet methylene concentrations in all flames. Aramco mech. and the present model are in good agreement with the measurements in stoichiometric flame, while in all rich flames only the present mechanism reproduces spatial profiles of 1CH2. Detailed analysis of the behaviour of these models revealed that omission of the reaction 1CH2+M=3CH2+M is the main reason of the discrepancy between predictions of the Aramco 1.3 and GRI-mech. 3.0 and experimental 1CH2 concentrations in rich flames.

Electron spectra of WO molecule. New electron state 3Π

The electron spectrum of the tungsten monooxide molecule is observed in the 550–800 nm region using intracavity laser absorption spectroscopy. The WO molecules are produced in a pulsed electric discharge through the mixture of tungsten hexacarbonyl vapors. The spectrum is recorded using a diffraction spectrometer (resolving power of 240000). The bands in the 16400–15500 cm–1 region are assigned to the 3Π0–X3Σ+ component of the 3Π0–X3Σ+–3XΣ+ electron transition. The rotational analysis of the 0-0 and 1-0 bands is carried out and the rotational constants for the ground X″3Σ and the exited 3Π0 states are computed: В′ = 0.385738 cm–1, B″ = 0.415538 cm–1.

The near-infrared spectrum of NiCl: Analysis of vibrational components of system G and system H between 12,500 cm−1 and 13,750 cm−1

The near-infrared spectrum of nickel chloride, NiCl, has been recorded at high resolution from 12,400–12,600cm−1, 13,200–13,500cm−1, and 13,600–13,750cm−1 using intracavity laser absorption spectroscopy, ILS. The NiCl molecules were produced in the plasma discharge of a nickel-lined, copper hollow cathode with ∼1.8torr of Ar as the sputter gas and a trace amount of CCl4 as the chloride source. Several transitions were observed and analyzed, including the (2,0), (1,0), and (0,1) bands of the [13.0] 2Π3/2–X2Π3/2 transition, System G, and the (1,0) band of the [12.3] 2Σ−–X2Π3/2 transition, System H. The transitions were analyzed using PGOPHER and obtained molecular parameters are reported. A potential energy curve for the [13.0] 2Π3/2 state has been constructed using the vibrational information from the analyzed transitions.

A method for separation of overlapping absorption lines in intracavity gas detection

We propose a novel method to separate overlapping absorption lines in gas detection based on fiber laser intracavity absorption spectroscopy. The method combines continuous wavelet transform, linear regression analysis and chaos particle swarm optimization together to retrieve the respective absorbance distributions of overlapping lines. The method’s principle is outlined and the rules for parameter selection are given. The performance of the method is demonstrated by both the simulated and experimental data. When the method is applied to the mixed gas concentration calibration of CO and CO2, high linearity is obtained with linear correlation coefficients of 0.9996 and 0.9997 respectively. The relative errors of CO and CO2 concentration retrieval are no more than 0.93% and 1.13% respectively.

A Gas Cell Based on Hollow-Core Photonic Crystal Fiber (PCF) and Its Application for the Detection of Greenhouse Gas (GHG): Nitrous Oxide (N2O)

The authors report the detection of nitrous oxide gas using intracavity fiber laser absorption spectroscopy. A gas cell based on a hollow-core photonic crystal fiber was constructed and used inside a fiber ring laser cavity as an intracavity gas cell. The fiber laser in the 1.55 μm band was developed using a polarization-maintaining erbium-doped fiber as the gain medium. The wavelength of the laser was selected by a fiber Bragg grating (FBG), and it matches one of the absorption lines of the gas under investigation. The laser wavelength contained multilongitudinal modes, which increases the sensitivity of the detection system. N2O gas has overtones of the fundamental absorption bands and rovibrational transitions in the 1.55 μm band. The system was operated at room temperature and was capable of detecting nitrous oxide gas at sub-ppmv concentration level.

Intracavity multigas detection based on multiband fiber ring laser

We present a new method for multigas detection based on multiband fiber ring laser. Wavelength division multiplexing is used to realize multiband laser operation. Laser intracavity absorption spectroscopy combined with wavelength modulation technique is used to improve the measurement sensitivity. The second harmonic signal is extracted by the software-based lock-in algorithm for gas concentration retrieval. The relationship between the harmonic amplitudes and gas concentrations is investigated under both weak absorption and strong absorption to improve the accuracy of concentration retrieval. When the system is applied to detect the mixed gases of acetylene, carbon monoxide and carbon dioxide in C+L band, the minimum detectable concentrations are 0.6ppm, 17.4ppm and 19.2ppm respectively.

Intracavity Laser Absorption Spectroscopy Study of HCO Radicals during Methane to Hydrogen Conversion in Very Rich Flames

Stoichiometric and very rich flames of methane have been investigated using nonintrusive laser diagnostics. Absolute concentration profiles of HCO were measured by intracavity laser absorption spectroscopy, and temperature profiles were obtained with laser-induced fluorescence of OH. Premixed CH4 + O2 + N2 flames were stabilized at a pressure of 30 ± 0.3 Torr. These new experimental data were compared with predictions of two models: GRI-mech. 3.0 and Aramco mech. 1.3. GRI-mech. performs better in a stoichiometric flame, whereas Aramco mech. is in better agreement with experiments in the rich flames. Detailed analysis of the behavior of these two models revealed that similar performance is essentially fortuitous and explained by balancing of different reactions involved in HCO formation and consumption.

A fiber laser intracavity absorption spectroscopy (FLICAS) sensor for simultaneous measurement of CO and CO2 concentrations and temperature

We report a method for the simultaneous measurement of carbon dioxide (CO2) and carbon monoxide (CO) absolute concentrations and temperature using fiber laser intracavity absorption spectroscopy (FLICAS). FLICAS uses an erbium-doped broadband laser capable of being tuned in the range 6350–6450cm−1. The range 6390–6410cm−1, which is emitted by the laser without tuning, allows for simultaneous observation of the CO, CO2, and methane (CH4) spectra. Truly simultaneous observation of these spectra is possible during one laser pulse with duration as short as 3.7μs. The sensitivity of the CO measurement is about 20 times higher than that of CO2, a feature which is advantageous for several applications. The concentration of CO can be measured with a sensitivity of 400ppm at room temperature, and this sensitivity can be improved by increasing the generation time. The experiments were performed in a temperature and flow-controlled cell in order to evaluate the accuracy of the concentration and temperature measurements from 296 to 1200K. The measured spectra of CO and CO2 are well described by the HITRAN database, allowing for accurate and simultaneous determination of CO, CO2 and temperature. The temperature is evaluated using the CO2 spectrum, which includes many “hot” transitions. The CH4 HITRAN data are deficient at high temperatures, so this method only allows for the evaluation of methane concentrations at room temperature.

New Perspectives in Monitoring the Flame Synthesis of Iron Oxide Nanoparticles: Addressing Solid and Gas-Phase Diagnostics Challenges

ABSTRACTSeveral techniques for in-situ monitoring and characterization of flame synthesized nanoparticles are described with the goal of gaining further insight into the mechanisms governing nanoparticle (NP) formation in flame reactors. These include: a combined particle mass spectrometer - quartz crystal microbalance apparatus (PMS-QCM); The Light Induced Detuning –Quartz Crystal Microbalance (LID-QCM) method; Application of Intra Cavity Laser Absorption Spectroscopy (ICLAS) for monitoring gas phase intermediates in a particle laden environment.

Near-infrared spectrum of ZrF by intracavity laser absorption spectroscopy

The (1,1) band of the CΩ=3/2−X2Δ3/2 transition of ZrF has been recorded at high resolution using intracavity laser absorption spectroscopy. The ZrF molecules were produced using a Zr-lined copper hollow cathode sputter source with a trace amount of SF6 as a fluoride source. Molecular constants from the analysis are presented and compared with previous work.