Intracavity Absorption Spectroscopy Research Articles

Atomic-level-mixing contribution to the P,T -odd Faraday effect as an enhancement factor in the search for P,T -odd interactions in nature

Recently, a $\mathcal{P},\mathcal{T}$-odd Faraday effect (PTFE), optical rotation in an external electric field parallel to the light propagation direction, was discussed as a promising tool for observation of the electron electric dipole moment in the intracavity absorption spectroscopy with atoms or molecules. The main mechanism leading to this effect, the linear Stark splitting of atomic levels (PTFE, LS) is well known. This mechanism is similar to the Zeeman splitting mechanism in case of the ordinary Faraday effect, i.e., optical rotation in an external magnetic field. In this paper we analyze the other possible mechanisms of PTFE, in particular, the atomic-level-mixing mechanism (PTFE, LM). In our analysis we perform considering PTFE (as well as the ordinary FE) as a kind of electro- (magneto-) optical circular birefringence. For the ordinary FE the level-mixing mechanism (FE, LM) is known apart from the main Zeeman level splitting mechanism (FE, LS). However, (PTFE, LM) mechanism for the PTFE was never considered in literature. Usually, the (FE, LS) mechanism dominates and the same was expected for (PTFE, LS). We demonstrate, however, that with heavy diatomic molecules, in particular in PbF, the contribution of (PTFE, LM) may essentially exceed the (PTFE, LS). This promises an additional enhancement of $\mathcal{P},\mathcal{T}$-odd effects in experiments with PbF molecule and makes this molecule one of the best candidates for performing such experiments.

Intracavity absorption spectroscopy of HCl isotopes, H2O, CH4, C2H4, and C2H6 in the 3.1-3.4 µm spectral range using a Cr:CdSe laser.

We demonstrate the first application of a Cr:CdSe laser for highly-sensitive multicomponent intracavity absorption spectroscopy around λ = 3.1-3.4 µm. A detection scheme based on an integrated recording of multiple (∼70) individual Cr:CdSe laser pulses after a single pump-pulse excitation is reported. The sensitivity of our system corresponds to an effective absorption path length of Leff ≈ 850 m. Exemplary measurements of atmospheric H2O and CH4, and additionally introduced gas-phase HCl, C2H4, or C2H6 are presented. The achieved noise-equivalent detection limits are in the ppb range. Possibilities for further sensitivity enhancement by up to a factor of 104 are discussed.

Two-Mode Biomedical Sensor Build-up: Characterization of Optical Amplifier

Intracavity absorption spectroscopy is a strikingly sensitive technique that has been integrated with a two-wavelength setup to develop a sensor for human breath. Various factors are considered in such a scenario, out of which Relative Intensity Noise (RIN) has been exploited as an important parameter to characterize and calibrate the said setup. During the performance of an electrical based assessment arrangement which has been developed in the laboratory as an alternative to the expensive Agilent setup, the optical amplifier plays a pivotal role in its development and operation, along with other components and their significance. Therefore, the investigation and technical analysis of the amplifier in the system has been explored in detail. The algorithm developed for the automatic measurements of the system has been effectively deployed in terms of the laser's performance. With this in perspective, a frequency dependent calibration has been pursued in depth with this scheme which enhances the sensor's efficiency in terms of its sensitivity. In this way, our investigation helps us in a better understanding and implementation perspective of the proposed system, as the outcomes of our analysis adds to the precision and accuracy of the entire system.

Formula omitted]-odd Faraday rotation in intracavity absorption spectroscopy with particle beam as a possible way to improve the sensitivity of the search for the time reflection noninvariant effects in nature

Possible experiments on the observation of the P,T - odd Faraday effect (rotation of polarization plane for the light, propagating through a medium in the presence of an external electric field, P - is the space inversion, T - is the time reflection) caused by the electron electric dipole moment in atoms and molecules, are discussed theoretically. An observation is assumed to be performed on the basis of modern intra-cavity absorption spectroscopy (ICAS) combined with atomic (molecular) beam techniques. The P,T - odd optical rotation is due to the linear Stark splitting of atomic or molecular levels. This leads to the difference between the refractive indexes for the right and left circularly polarized photons.

Room-temperature Fe:ZnSe laser tunable in the spectral range of 3.7-5.3 µm applied for intracavity absorption spectroscopy of CO2 isotopes, CO and N2O.

We demonstrate an intracavity absorption spectroscopy system based on a broadband single-crystal pulsed Fe:ZnSe laser. The laser operates at room-temperature and is continuously tunable in the spectral range of 3.76-5.29 µm. The long-wavelength emission up to 5.29 µm is a record achievement for Fe:ZnSe lasers, to the best of our knowledge. The developed laser system is applied for measurements of gaseous absorption inside the laser resonator. We demonstrate sensitive detection of (i) CO2 isotopes in the atmosphere and in human breath, (ii) CO in breath (after cigarette smoking) and in the smoke of a smoldering paper, and (iii) N2O in a gas flow. The achieved detection limits are: 0.1 ppm for 12CO2 and 13CO2, 3 ppm for CO, and 1 ppm for N2O. The sensitivity of the current system is primarily limited by the short pump-pulse duration of 40 ns. Possibilities for sensitivity enhancement by up to a factor of 107 are discussed.

Photon-spin-dependent contribution to the -odd Faraday rotation effect for atoms

The photon-spin-dependent (PS) contribution to the ordinary Faraday effect—optical rotation in an external magnetic field is well known. This contribution is proportional to factor where is the photon spin. Recently a -odd Faraday effect—optical rotation in an external electric field —was discussed as a promising tool for observation of the electron electric dipole moment in the intra-cavity absorption spectroscopy. In the present paper, we introduce the PS contribution to the -odd Faraday rotation effect. This contribution is proportional to and has to be taken into account in the calculations of the -odd Faraday effect.

Determination of gas-phase absorption cross-sections of FeO in a shock tube using intracavity absorption spectroscopy near 611 nm

We report state-resolved absorption cross-section measurement and oscillator-strength evaluation of the gas-phase iron oxide (FeO) orange system near 611 nm. Intracavity absorption spectroscopy (ICAS) with a homemade broadband dye laser was applied for time-resolved measurements of absorption spectra of shock-activated mixtures of iron pentacarbonyl and carbon dioxide (diluted in argon), generating gas-phase FeO. The measurements were performed with a time resolution of 170 µs in the spectral range of 16,316–16,353 cm−1 that includes a large number of FeO absorption lines. Across the 8-cm diameter of the shock tube, ICAS leads to an effective absorption path length of 260 m. Absorption cross-section values of 0.5 × 10–18–4 × 10–18 cm2 were determined for temperatures around 2200 K and pressures of ∼1.3 bar. Pressure- and temperature-independent oscillator strengths for individual ro-vibronic transitions within the 611-nm band of FeO orange system are reported for the first time. These data are generally applicable for quantitative absorption measurements of flame studies of iron chemistry, where FeO plays a key role as intermediate species.

Gas/liquid detection system based on intra-cavity absorption spectroscopy and tilted fiber Bragg grating

Abstract A gas/liquid detection system is developed based on the intra-cavity absorption spectroscopy (ICAS) and a tilted fiber Bragg grating (TFBG). Multiple gases such as acetylene, carbon monoxide and ammonia gas with absorption lines within C-band can be detected using the proposed scheme. The wavelength sweeping range can be controlled to obtain a specific number of absorption lines to meet the requirements on different measurement accuracy. In this work, a TFBG structure is introduced into the ICAS technique to realize the sensing of liquid refractive index. The TFBG works around the wavelength of 1550 nm, which allows a long-distance signal transmission and a flexible system adjustment. The proposed system has been applied to detect the concentration of acetylene with an absolute error of less than 46 ppm. In addition, a set of glycerol-water solutions with refractive indices from 1.3959 to 1.4430 have been measured using the proposed scheme with a sensitivity of 528.2 nm/RIU.

Optical Rotation Approach to Search for the Electric Dipole Moment of the Electron

The P , T -odd Faraday effect (i.e., rotation of the polarization plane of light propagating through a medium in presence of the external electric field due to P , T symmetry violating interactions) is considered for several atomic species: Ra, Pb, Tl, Hg, Cs, and Xe. Corresponding theoretical simulation of P , T -odd Faraday experiment, with already achieved intracavity absorption spectroscopy characteristics and parameters, is performed. The results show that the magnetic dipole transitions in the Tl and Pb atoms as well as the electric dipole transitions in the Ra, Hg and Cs atoms are favorable for the observation of the P , T -odd Faraday optical rotation. The estimation of the rotation angle of the light polarization plane demonstrates that recently existing boundaries for the electron electric dipole moment can be improved by one-two orders of magnitude.

Evaluation of the P, T -odd Faraday effect in Xe and Hg atoms

Accurate evaluation of the $\mathcal{P}$,$\mathcal{T}$-odd Faraday effect (rotation of the polarization plane for the light propagating through a medium in presence of an external electric field) is presented. This effect can arise only due to the $\mathcal{P}$,$\mathcal{T}$-odd interactions and is different from the ordinary Faraday effect, i.e. the light polarization plane rotation in an external magnetic field. The rotation angle is evaluated for the ICAS (intracavity absorption spectroscopy) type experiments with Xe and Hg atoms. The results show that Hg atom may become a good candidate for a search for the $\mathcal{P}$,$\mathcal{T}$-odd effects in atomic physics.

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.

P, T -odd Faraday rotation in heavy neutral atoms

Accurate evaluation of the $\mathcal{P},\mathcal{T}$-odd Faraday effect (rotation of the polarization plane of the light propagating through a medium in the presence of an external electric field) is presented. The magnitude of this rotation is directly proportional to the optical path length. A novel idea is to observe the $\mathcal{P},\mathcal{T}$-odd Faraday effect using intracavity absorption spectroscopy (ICAS) experiments. The modern ICAS experiments allow one to observe the rotation of the light polarization plane (natural or $\mathcal{P}$-odd) with the optical path length up to a hundred kilometers. This can be done mainly due to the work off-line in the resonance absorption experiments. For the Faraday rotation (ordinary or $\mathcal{P},\mathcal{T}$-odd) the maximum of the effect coincides with the maximum of absorption which usually prevents the work off-line and employment of the large optical path length. However, we propose to use the second rotation maximum that exists for the Faraday effect and would also allow for work off-line. The calculations are performed for the heavy metal atoms Cs, Tl, Pb, and Ra where the $\mathcal{P},\mathcal{T}$-odd effects are most pronounced. The results of the calculations demonstrate that with the large optical path length the ICAS experiments will be able to fix the possible $\mathcal{P},\mathcal{T}$-odd effects at a level comparable with other very advanced modern experiments.

Investigation of Cavity Length and Mode Spacing Effects in Dual-Mode Sensor

Utilizing the principles of intracavity absorption spectroscopy, a biomedical sensor has been developed. The unique feature is the deployment of dual-mode competition which renders characteristics of feasibility, cost, and investigation in various domains. Insight of the high sensitivity of this sensor, relative intensity noise (RIN) is being explored as one of the detection parameters. Cavity length and mode spacing effects of the sensor on average RIN have been investigated to optimize these parameters for improvement in RIN response of the sensor. It has been found that operating the sensor for increased mode spacing improves its RIN response by 24%. In this mode of operation, change in cavity length has almost negligible effect on RIN response of the sensor. This fact in the proposed sensor system can be used to detect various trace gases with minute concentration levels thereby revealing important information about specific diseases in human body.

A broadband Tm/Ho-doped fiber laser tunable from 1.8 to 2.09 µm for intracavity absorption spectroscopy

A broadband tunable Tm/Ho-doped fiber laser is developed for sensitive in situ measurements of intracavity absorption spectra in the spectral range of 4780–5560 cm−1. This spectral range includes an atmospheric transmission window enabling sensitive measurements of various species. The spectral bandwidth of laser emission varies from 20 to 60 cm−1 and is well suitable for multicomponent spectroscopy. The sensitivity achieved in cw operation corresponds to an effective absorption path length of Leff = 20 km, with a spectral noise of less than 1%. The spectroscopic system is applied for measurements of absorption spectra of H2O, NH3 and for simultaneous in situ detection of three isotopes of CO2 in human breath, which is important for medical diagnostics procedures.

Intracavity absorption spectroscopy of formaldehyde from 6230 to 6420 cm−1

We apply intracavity absorption spectroscopy for measurements of the absorption spectrum of formaldehyde, CH2O, from 6230 to 6420 cm−1, of which only a small fraction (6351–6362 cm−1) has been recorded elsewhere. The measurements are performed in the cavity of a broadband Er3+-doped fiber laser, with a sensitivity corresponding to the effective absorption path length of 45 m and a spectral resolution of 0.1 cm−1. The noise-equivalent detection limit of CH2O achieved with the strongest absorption line at 6252.64 cm−1 is estimated to be 5 ppm. High tolerance to broadband losses and the accessible time resolution of 50 µs make it possible to apply this detection system for time-resolved monitoring of CH2O together with other molecules in harsh combustion environments, e.g., in combustion engines.

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

Graphene intracavity spaser absorption spectroscopy

We propose an intracavity plasmon absorption spectroscopy method based on graphene active plasmonics. It is shown that the plasmonic cavity contribution to the sensitivity is proportional to the quality factor Q of the graphene plasmonic cavity and reaches two orders of magnitude. The addition of gain medium into the cavity increases the sensitivity of method. Maximum sensitivity is reached in the vicinity of the plasmon generation threshold. The gain contribution to the sensitivity is proportional to Q1/2. The giant amplification of sensitivity in the graphene plasmon generator is associated with a huge path length, limited only by the decoherence processes. An analytical estimation of the sensitivity to loss caused by analyzed particles (molecules, nanoparticles, etc.) normalized by the single pass plasmon scheme is derived. Usage of graphene nanoflakes as plasmonic cavity allows a high spatial resolution to be reached, in addition to high sensitivity.

Time-resolved detection of temperature, concentration, and pressure in a shock tube by intracavity absorption spectroscopy

In this paper, we demonstrate the first application of intracavity absorption spectroscopy (ICAS) for monitoring species concentration, total pressure, and temperature in shock-tube experiments. ICAS with a broadband Er3+-doped fiber laser is applied to time-resolved measurements of absorption spectra of shock-heated C2H2. The measurements are performed in a spectral range between 6512 and 6542 cm−1, including many absorption lines of C2H2, with a time resolution of 100 µs and an effective absorption path length of 15 m. Up to 18-times increase of the total pressure and a temperature rise of up to 1200 K have been monitored. Due to the ability of simultaneously recording many absorption lines in a broad spectral range, the presented technique can also be applied to multi-component analysis of transient single-shot processes in reactive gas mixtures in shock tubes, pulse detonation engines, or explosions.

Sensitivity to electron-to-proton mass ratio variation from 12C2H2 rovibrational transitions to v1 + v3 and v1 + v2 + v4 + v5 interacting levels

Calculations of the sensitivity to a variation of the electron-to-proton mass ratio μ for 12C2H2 transitions of the v1+v3 and v1+v2+v4+v5 bands in the spectral region at 1.5μm are presented. They account for the Fermi and l-type rotation and vibration resonances of the excited states. The frequency splittings between near resonant transitions, arising from a cancellation of effective rotational intervals with frequency shifts associated to the vibrational band origin, the anharmonicity and the rotation-vibration interactions, have sensitivity coefficients to a variation of μ of both signs in the range of 10–103. The measurements of temporal drifts of frequency splittings against the Cs frequency standard have the potential to better constrain a variation of μ comparing to that of other fundamental constants. The systematic frequency shifts for frequency splittings are discussed for experimental setups based on intracavity saturated absorption spectroscopy and the constraint of a measurement of a fractional variation of μ is projected at 10−10 level.

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.