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X-ray transient absorption spectroscopy by an ultrashort x-ray-laser pulse in a continuous-wave IR field
摘要： X-ray transient absorption spectra (XTAS) of molecules are theoretically investigated in a femtosecond x-ray pump and continuous-wave (cw) infrared (IR)-control scenario. The scheme is exemplified by a CO molecule resonantly pumped into carbon and oxygen core-excited 1s → π ? states by a weak femtosecond x-ray pulse, while dynamic Stark shifts are induced by the cw IR-control radiation. As a result, significant shoulder structures appear in XTAS showing strong dependence on the phase of IR radiation relative to the envelope of the x-ray pulse. Due to a significant difference in the frequencies of the two pulses, the present XTAS scheme provides much clear interpretation of the dynamic Stark effects as compared to the attosecond UV transient absorption scenario. Within the suggested two-level model, where the total spectrum is decomposed as incoherent superposition of contributions from different vibrational excitations weighted by the Franck-Condon Factors, all spectral structures can be well identified and interpreted in a good agreement with the full-scale molecular simulations. Well-characterized XTAS in the proposed IR-control scheme can be applied for fine phase synchronization between IR and x-ray pulses, highly demanded in modern experiments on x-ray free-electron lasers.
关键词： X-ray transient absorption spectroscopy,continuous-wave IR field,Franck-Condon Factors,dynamic Stark shifts,ultrashort x-ray-laser pulse
更新于2025-09-16 10:30:52
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Quantitative measurements of formaldehyde in the low-temperature oxidation of iso-octane using mid-infrared absorption spectroscopy
摘要： Time-resolved quantitative measurements of formaldehyde (HCHO) in the low-temperature oxidation of iso-octane using a rapid compression machine have been performed with mid-infrared laser absorption spectroscopy. Due to the weak interference of the broadband absorption of iso-octane, a two-color detection scheme was applied to HCHO detection. The cross-sections of HCHO and iso-octane in two colors were measured using the rapid compression machine in the temperature range of 450–737 K and pressure range of 100–700 kPa. The time-resolved quantitative HCHO profiles in the low-temperature oxidation of iso-octane at 0.77 MPa, 645 K, and an equivalence ratio of 1.0 were successfully obtained. The calculated HCHO profiles using the latest chemical kinetic model of iso-octane show the same tendency as the experimental profiles.
关键词： formaldehyde,mid-infrared absorption spectroscopy,iso-octane,low-temperature oxidation,rapid compression machine
更新于2025-09-16 10:30:52
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Near-infrared tunable diode laser absorption spectroscopy-based determination of carbon dioxide in human exhaled breath
摘要： A spectroscopic detection system for the accurate monitoring of carbon dioxide (CO2) in exhaled breath was realized by tunable diode laser absorption spectroscopy (TDLAS) in conjunction with a vertical-cavity surface-emitting laser (VCSEL) and a multipass cell with an effective optical path-length of 20 m. The VCSEL diode emitting light with an output power of 0.8 mW, covered the strong absorption line of CO2 at 6330.82 cm?1 by drive-current tuning. The minimum detectable concentration of 0.769% for CO2 detection was obtained, and a measurement precision of approximately 100 ppm was achieved with an integration time of 168 s. Real-time online measurements were carried out for the detection of CO2 expirograms from healthy subjects, different concentrations were obtained in dead space and alveolar gas. The exhaled CO2 increased significantly with the increasing physical activity, reaches its maximal value at the beginning of respiratory compensation and then decreased slightly until maximal exercise. The developed measurement system has a great potential to be applied in practice for the detection of pulmonary diseases associated with CO2 retention.
关键词： CO2,human health monitoring,Tunable diode laser absorption spectroscopy,carbon dioxide,VCSEL,exhaled breath,TDLAS,vertical-cavity surface-emitting laser
更新于2025-09-16 10:30:52
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Selective Chemical Enhancement via Graphene Oxide in Infrared Attenuated Total Reflection Spectroscopy
摘要： Graphene oxide (GO) as a readily prepared graphene derivative comprises negatively charged oxygenated functional groups, and a mixture of sp2 and sp3 carbon domains. In comparison with hydrophobic graphene, GO is characterized by superior water dispersibility, and may non-covalently interact with a significantly wider range of molecules. Taking advantage of GO and infrared attenuated total reflection spectroscopy (IR-ATR), an efficient strategy enabling unprecedented absorption signal amplification via chemical enhancement of various molecular species in aqueous environment was demonstrated in this study. The evolution of selectively enhanced molecular fingerprints across the entire mid-infrared spectral range was in situ monitored in real time, while retaining the characteristic molecular IR absorptions, and confirms the utility of GO as a suitable and versatile material in surface-enhanced infrared absorption spectroscopy (SEIRA) scenarios.
关键词： Infrared attenuated total reflection spectroscopy,Graphene oxide,Chemical enhancement,Aqueous environment,Surface-enhanced infrared absorption spectroscopy
更新于2025-09-12 10:27:22
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[IEEE 2019 Conference on Lasers and Electro-Optics Europe & European Quantum Electronics Conference (CLEO/Europe-EQEC) - Munich, Germany (2019.6.23-2019.6.27)] 2019 Conference on Lasers and Electro-Optics Europe & European Quantum Electronics Conference (CLEO/Europe-EQEC) - Extended-Cavity-Quantum-Cascade-Laser-Voltage Intracavity Sensing and Application to Atmospheric Gas Detection
摘要： Laser spectrometers based on Quantum Cascade Lasers (QCL) provide good results for gas sensing in terms of sensibility and selectivity thanks to the characteristics of these sources. Distributed feedback (DFB) configuration provides narrow linewidth that enhances selectivity and their emission in the mid-IR enables to reach the fundamental absorption bands of molecules. The main limitation of these sources is their narrow tuning range (~ 10 cm-1) that prevents from monitoring complex species with broad absorption spectra or realizing multi-gas sensing. To obtain a broader tuning range, one solution consists of QCL DFB array with an arrayed waveguide grating to perform multi-species spectroscopy [1]. A more common technique is to implement the laser in an external cavity system. In GSMA, a commercial Extended-Cavity Quantum Cascade Laser emitting at 10.5 μm has been used to demonstrate photoacoustic gas sensing of heavy molecules such as butane [2] and a lab-made EC-QCL emitting at 7.5 μm was developed for detection of acetone and POCl3 in gas phase [3]. Moreover, the use of an external cavity allows the possibility to perform Intra-Cavity Laser Absorption Spectroscopy (ICLAS). In this method the sample is placed within the laser resonator. Absorption lines of the sample imprint signatures on the spectrum because they influence it during many round trips. The cavity output light is detected to perform spectroscopy. The used QCL developed by mirSense is operated in cw operation at room temperature and emits from 7.4 to 7.8 μm. A technique using the QCL compliance voltage [4] called EVIS (EC-QCL Voltage Intracavity Sensing) is used to retrieve the spectrum of the gas inside the cavity. This way no detector outside the cavity is needed. With gas inside the cavity, losses rise implies a variation of intracavity intensity thus a variation of laser voltage. The large wavenumber sweeping is performed through the grating rotation and the variation of QCL current supply permits to obtain a small wavelength variation. In order to suppress the QCL mode hops influence, a current ramp is applied so that the small wavelength total variation is equal to 1 QCL mod hop. Then QCL voltage is recorded during the current ramp, for all grating positions, and a numerical treatment is performed to improve the signal. Fig. 1 presents a result of this measurement (on the left) compared with the absorption coefficient calculated from the HITRAN database [www.hitran.org] (on the right). This measurement corresponds to a cavity filled with 0.3% of CH4 in air (containing water vapor) at atmospheric pressure. This preliminary result shows a good agreement between the voltage difference and the calculated absorption coefficient. The resolution is estimated to approx. 0.1 cm-1.
关键词： Quantum Cascade Lasers,gas sensing,ICLAS,Intra-Cavity Laser Absorption Spectroscopy,EVIS,EC-QCL Voltage Intracavity Sensing,QCL
更新于2025-09-12 10:27:22
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Mechanism of PbI2 situ-passivated perovskite films for enhancing performance of perovskite solar cells
摘要： Perovskite solar cells have brought tremendous research interests because of their tolerance of defects, low cost, and facile processing. In perovskite solar cells devices, PbI2 has been utilized to passivate defects at perovskite films surface and grain boundaries, yet a systematic mechanism of PbI2 situ-passivating for enhancing the efficiency has not been fully explored. Here, this work systematically studies the role of the precise PbI2 ratio, and the PbI2 situ-passivation mechanism based on trap density, carrier lifetime, and Fermi level etc. This study finds that the appropriate ratio of I:Pb is around 2.57:1 using energy dispersive spectroscopy. After the moderate excess PbI2 situ-passivating, the trap density is reduced from 6.12 × 1016 cm-3 to 3.38 × 1016 cm-3, and the carrier lifetime is extended from 168.35 ps to 368.77 ps by using femtosecond transient absorption spectroscopy. This result indicates that the moderate excess PbI2 situ-passivation can reduce the trap density and suppress non-radiative recombination. The efficiency of solar cell has realized a nearly 11.3% improvement of 19.55% for the I:Pb ratio of 2.57:1 compared with 2.69:1. It demonstrates that the efficiency can be enhanced effectively by PbI2 situ-passivation.
关键词： SnO2,EDS-mapping,transient absorption spectroscopy,perovskite solar cells,PbI2,passivation mechanism
更新于2025-09-12 10:27:22
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Spatially Resolved Measurements of Metastable Atom Density and Electric Field Strength in a Microhollow Cathode Helium Plasma by Laser Absorption Spectroscopy
摘要： We apply laser absorption spectroscopy to direct-current hollow-cathode helium plasma generated in a 0.3-mm-diameter cylindrical hole at gas pressures of 10 - 80 kPa. The measured transitions are 23S-23P and 21P-31D. We evaluate the helium metastable 23S density and gas temperature using the former transition and the 21P atom density and electric field strength from the latter one. The observed lateral distributions of the 23S and 21P atom densities depend on the gas pressure, which results from the sheath length estimated based on the spatial distribution of the evaluated electric field strength.
关键词： laser absorption spectroscopy,helium metastable,microhollow cathode discharges
更新于2025-09-12 10:27:22
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EXPRESS: Two-Dimensional Temperature Measurement in a High Temperature and Pressure Combustor Using Computed Tomography Tunable Diode Laser Absorption Spectroscopy (CT-TDLAS) with a Wide-Scanning Laser at 1335–1375 nm
摘要： Tunable diode laser absorption spectroscopy (TDLAS) technology is a developing method for temperature and species concentration measurements with the features of non-contact, high precision, high sensitivity, etc. The difficulty of two-dimensional (2D) temperature measurement in actual combustors has not yet been solved because of pressure broadening of absorption spectra, optical accessibility, etc. In this study, the combination of computed tomography (CT) and TDLAS with a wide scanning laser at 1335–1375 nm has been applied to a combustor for 2D temperature measurement in high temperature of 300–2000 K and high pressure of 0.1–2.5 MPa condition. An external cavity type laser diode with wide wavelength range scanning at 1335–1375 nm was used to evaluate the broadened H2O absorption spectra due to the high temperature and high pressure effect. The spectroscopic database in high temperature of 300–2000 K and high pressure of 0.1–5.0 MPa condition has been revised to improve the accuracy for temperature quantitative analysis. CT reconstruction accuracy was also evaluated in different cases, which presented the consistent temperature distribution between CT reconstruction and assumed distributions. The spatial and temporal distributions of temperature in the high temperature and high pressure combustor were measured successfully by CT-TDLAS using the revised spectroscopic database.
关键词： high temperature and high pressure field,TDLAS,computed tomography,2D,Two-dimensional temperature measurement,combustion,CT,tunable diode laser absorption spectroscopy
更新于2025-09-12 10:27:22
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A Sensitive and Reliable Carbon Monoxide Monitor for Safety-focused Applications in Coal Mine using a 2.33 μm Laser Diode
摘要： In this paper, a stable and reliable carbon monoxide (CO) monitoring system with high sensitivity (at sub-ppm level) was designed and demonstrated with particular reference to use in the mining industry, tailoring the design specifically for forecasting spontaneous combustion, a major hazard to miners. An appropriate strong CO absorption line was used to minimize the interferences expected from gases present in ambient air, with several preferred CO absorption lines selected and investigated, therefore choosing a distributed feedback (DFB) laser operating at a wavelength of 2330.18 nm as the excitation source. Through a detailed investigation, a minimum detection limit of ~0.2 ppm and a measurement precision of <50 ppb were achieved with a 1 s averaging time. Further long-term continuous monitoring evaluation was carried out, demonstrated the excellent stability and reliability of the developed CO monitor. The results obtained have validated the potential of this design of a CO monitoring system for practical monitoring applications underground to enhance safety in the mining industry.
关键词： mining industry,carbon monoxide,forecasting spontaneous combustion,direct absorption spectroscopy
更新于2025-09-12 10:27:22
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Terahertz differential absorption spectroscopy using multifurcated subnanosecond microchip laser
摘要： Using spectral multifurcated oscillations in a passively Q-switched microchip laser, we demonstrate frequency-domain differential absorption spectroscopy in the terahertz (THz) frequency region. Within a single quasi-continuous-wave (QCW) excitation, a microchip laser comprising a 7-mm-long Nd:YAG/Cr:YAG composite ceramic provides up to three subnanosecond pulses with a 1064-nm wavelength and a 50-Hz QCW repetition rate. We have observed that the longitudinal mode of double and triple pulses shows stable bifurcation and trifurcation, respectively, induced by a spatial hole burning effect within the laser cavity. These pulses are directly used to drive an injection-seeded THz-wave parametric generator based on a MgO-doped LiNbO3 crystal, thereby generating up to three monochromatic, self-frequency-switched THz-wave pulses separated from each other in frequency by a free spectral range of the laser cavity. By precisely tuning one of the THz-wave frequencies to the gas absorption line, multifurcated THz-wave pulses facilitate the measurement of differential absorption signals every 20 ms without any active frequency modulation. We also show that first- and second-order derivative spectra of gas absorption can be derived from a single frequency sweep of multifurcated pulses without a reference spectrum and computational derivation. Our approach paves the way toward realization of a THz differential absorption lidar for use in fast gas sensing applications.
关键词： differential absorption spectroscopy,terahertz,gas sensing,microchip laser,multifurcated oscillations
更新于2025-09-12 10:27:22