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Application of the least square method for processing the signal obtained by the tuneable diode laser absorption spectroscopy method in the range 4860a??4880a??cm <sup>a??1</sup> for the problem of measuring <sup>13</sup> CO <sub/>2</sub> content in exhaled air
摘要： The 1st, 2nd and 3rd order least square method (LSM-1, LSM-2 and LSM-3) is applied to smooth the experimental absorption signal of 13CO2 and 12CO2 obtained by the tuneable diode laser absorption spectroscopy method in the 4860–4880 cm?1 frequency range of a tuneable diode laser. It has been shown clearly that using LSM-2 with a filter window N ~ 100 allows the 13CO2 content in exhaled air to be measured at an error level of 0.28%, which meets breathing tests requirements.
关键词： gas analysis,biomedical analysis,carbon dioxide,tuneable diode laser absorption spectroscopy (TDLAS)
更新于2025-09-19 17:13:59
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Ppb-level formaldehyde detection system based on a 3.6???μm interband cascade laser and mode-locked cavity enhanced absorption spectroscopy with self-calibration of the locking frequency
摘要： A mid-infrared formaldehyde (H2CO) detection system was demonstrated using a continuous-wave distributed-feedback interband cascade laser (DFB-ICL) emitting at 3.6 μm as light source and an assembly F-P cavity with 20 m effective optical path length as gas chamber. The laser and the cavity were locked to the H2CO absorption peak simultaneously by an electro-optic modulation based automatic Pound-Drever-Hall (PDH) scheme which consist of two steps: dynamic PDH locking and continuous PDH locking. Before continuous PDH locking, the dynamic PDH locking was conducted to acquire the H2CO absorption spectrum and calibration the locking frequency. Then, the cavity transmitted intensity was detected continuously to characterize the gas concentration. H2CO measurements were conducted to evaluate the performance of the sensor system. A linear relationship was observed between the voltage of the absorption signal and the H2CO concentration within the range of 0–6 ppm. Based on Allan deviation analysis, a minimum detection limit of 5.8 ppb was achieved with an averaging time of 30 s.
关键词： Cavity enhanced absorption spectroscopy,Mid-infrared,Interband cascade laser,Formaldehyde detection
更新于2025-09-19 17:13:59
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Cross-band infrared laser absorption of carbon monoxide for thermometry and species sensing in high-pressure rocket flows
摘要： A novel cross-band laser absorption spectroscopy technique has been developed for quantitative measurements of gas temperature and carbon monoxide (CO) in high-pressure, high-temperature rocket combustion flows. The strategy enables a broad range of sensor operability by simultaneously probing rovibrational transitions in both the fundamental and first overtone bands of CO near 4.98 μm and 2.32 μm, respectively, which sustain large differences in temperature dependence despite collisional broadening. Scanned-wavelength modulation spectroscopy methods are integrated for noise rejection in the harsh rocket operating environment. Initial experiments using the cross-band thermometry technique have been conducted on a single-element-injector rocket combustor with RP-2/GOx and CH4∕GOx propellant combinations at pressures up to 75 bar. Measurements of the first overtone bandhead (2.32 μm) maintained adequate signal-to-noise at even higher pressures (up to 105 bar), although deviating significantly from spectral simulations. To account for collisional effects at high gas densities, empirical models for line mixing, developed via shock tube studies, were employed to enable quantitative interpretation of measured signals for temperature and CO mole fraction in the rocket combustor.
关键词： thermometry,high-pressure rocket flows,species sensing,carbon monoxide,cross-band laser absorption spectroscopy
更新于2025-09-19 17:13:59
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Multipolar terahertz absorption spectroscopy ignited by graphene plasmons
摘要： Terahertz absorption spectroscopy plays a key role in physical, chemical and biological systems as a powerful tool to identify molecular species through their rotational spectrum fingerprint. Owing to the sub-nanometer scale of molecules, radiation-matter coupling is typically dominated by dipolar interaction. Here we show that multipolar rotational spectroscopy of molecules in proximity of localized graphene structures can be accessed through the extraordinary enhancement of their multipolar transitions provided by terahertz plasmons. In particular, specializing our calculations to homonuclear diatomic molecules, we demonstrate that a micron-sized graphene ring with a nano-hole at the core combines a strong near-field enhancement and an inherently pronounced field localization enabling the enhancement of the dipole-forbidden terahertz absorption cross-section of H+2 by 8 orders of magnitude. Our results shed light on the strong potential offered by nano-structured graphene as a robust and electrically tunable platform for multipolar terahertz absorption spectroscopy at the nanoscale.
关键词： graphene plasmons,multipolar transitions,nanoscale,Terahertz absorption spectroscopy
更新于2025-09-19 17:13:59
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Photoswitching mechanism of a fluorescent protein revealed by time-resolved crystallography and transient absorption spectroscopy
摘要： Reversibly switchable fluorescent proteins (RSFPs) serve as markers in advanced fluorescence imaging. Photoswitching from a non-fluorescent off-state to a fluorescent on-state involves trans-to-cis chromophore isomerization and proton transfer. Whereas excited-state events on the ps timescale have been structurally characterized, conformational changes on slower timescales remain elusive. Here we describe the off-to-on photoswitching mechanism in the RSFP rsEGFP2 by using a combination of time-resolved serial crystallography at an X-ray free-electron laser and ns-resolved pump–probe UV-visible spectroscopy. Ten ns after photoexcitation, the crystal structure features a chromophore that isomerized from trans to cis but the surrounding pocket features conformational differences compared to the final on-state. Spectroscopy identifies the chromophore in this ground-state photo-intermediate as being protonated. Deprotonation then occurs on the μs timescale and correlates with a conformational change of the conserved neighbouring histidine. Together with a previous excited-state study, our data allow establishing a detailed mechanism of off-to-on photoswitching in rsEGFP2.
关键词： time-resolved crystallography,fluorescent proteins,transient absorption spectroscopy,photoswitching,rsEGFP2
更新于2025-09-19 17:13:59
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Simultaneous Measurements of Light Hydrocarbons Using Supercontinuum Laser Absorption Spectroscopy
摘要： Simultaneous measurements of light hydrocarbon species based on near-infrared (near-IR) supercontinuum laser absorption spectroscopy (SCLAS) are demonstrated. SCLAS is a broadband absorption diagnostic technique that provides significant advantages over existing absorption diagnostic techniques. Coupled with a fast spectrum analysis strategy, accurate measurements of multiple hydrocarbon concentrations can be made concurrently. Methane (CH4), acetylene (C2H2), ethylene (C2H4), and their mixtures were probed near ambient temperature and pressure conditions. Light hydrocarbons are found in many fuel and energy applications, and a sensor that can accurately and simultaneously probe multiple species’ concentrations and temperature would greatly enhance measurement versatility. Absorption spectra of the three hydrocarbon species were measured between 1.5 and 1.7 μm in this study. These spectra can be very convoluted, where broad absorption features interfere with neighboring features, be it from the same or different species. Species concentrations and temperatures were resolved using a spectrum analysis strategy based on linear regression. Experimental results showed good agreement with test conditions even in the presence of significant spectral overlap.
关键词： supercontinuum laser absorption spectroscopy,light hydrocarbons,spectrum analysis strategy,simultaneous measurements,near-infrared
更新于2025-09-19 17:13:59
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Zn1 a?? xCdxS Nanoparticles Obtained by Laser Ablation
摘要： Approximately spherical nanoparticles of the II–VI semiconductor materials Zn1 – xCdxS have been produced successfully by laser ablation of the bulk material in several liquids. The non-stabilized suspensions of particles are characterized by absorption spectroscopy and transmission electron microscopy (TEM). The procedure is not strongly size-selective, radii of 7 ± 3 nm were found for Zn1 – xCdxS by transmission electron microscopy. Acetonitrile stabilizes the particles for several days up to weeks. Prolonged irradiation leads effectively to a reduction in particles size, in which particle agglomeration may play an important role. Ablation in degassed liquids does not have a significant effect on the absorption of the suspended particles.
关键词： Zn1 – xCdxS nanoparticles,laser ablation,absorption spectroscopy,transmission electron microscopy,quantum confinement
更新于2025-09-19 17:13:59
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Near-Infrared Tunable Laser Absorption Spectroscopic Acetylene Sensor System Using a Novel Three Mirror-Based, Dense Pattern Gas Cell
摘要： By contrast with the widely reported traditional two mirror‐based Herriott cell, a three mirror‐based dense pattern gas cell was proposed, of which the modeling and design were proven to be effective through a comparison between the simulated spot pattern and effective path length and those of the experimental results. A mechanical structure was designed to adjust the position/angle of the three mirrors for aligning the optical path. The experimentally measured reflection number was 60, resulting in an optical path length of ~11 m, which agrees well with the theoretical value of 10.95 m. Combined with a near‐infrared laser with a center wavenumber located at an acetylene (C2H2) absorption line of 6521.2 cm?1, a C2H2 sensor system was established to verify the feasibility of the three mirror‐based gas cell. Assisted by a data acquisition (DAQ) card, a LabVIEW platform was developed to generate the drive signal of the laser and acquire the second harmonic (2f) signal from the output of the detector. Through Allan variance analysis, the limit of detection (LoD) of the sensor system is 4.36 ppm at an average time of 0.5 s; as the average time exceeds 10 s, the LoD is <1 ppm. The proposed model and design of the three mirror‐based gas cell can be used to realize similar gas cells with different absorption path lengths for gas detection based on infrared absorption spectroscopy.
关键词： laser absorption spectroscopy,multipass gas cell,acetylene detection,wavelength modulation spectroscopy
更新于2025-09-16 10:30:52
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[IEEE 2019 44th International Conference on Infrared, Millimeter, and Terahertz Waves (IRMMW-THz) - Paris, France (2019.9.1-2019.9.6)] 2019 44th International Conference on Infrared, Millimeter, and Terahertz Waves (IRMMW-THz) - Terahertz Differential Absorption Spectroscopy Using Multi-Furcated Nd:YAG Microchip Laser for Gas Sensing
摘要： We demonstrate a frequency-domain differential absorption spectroscopy in the terahertz (THz) range for gas sensing applications. Our system is based on an injection-seeded THz-wave parametric generator driven by a multi-furcated Nd:YAG microchip laser. Within a single excitation cycle of the laser, the is-TPG generates up to three narrowband THz-wave pulses that are separated from each other in time by 78 μs and in frequency by 11 GHz, which is due to the spatial hole burning effect in the laser cavity. These pulses can be directly used to measure differential absorption signals, and first and second derivative spectra of target gas molecules without measuring reference spectra.
关键词： Nd:YAG microchip laser,gas sensing,differential absorption spectroscopy,THz-wave parametric generator,terahertz
更新于2025-09-16 10:30:52
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Simultaneous Measurements of Soil CO and CH Fluxes Using Laser Absorption Spectroscopy
摘要： We present a method of simultaneously measuring soil CO2 and CH4 fluxes using a laser-based cavity ring-down spectrometer (CRDS) coupled to an automated non-steady-state chamber system. The differential equation describing the change in the greenhouse gas (GHG) mixing ratio in the chamber headspace following lid closure is solved for the condition when a small flow rate of chamber headspace air is pulled through the CRDS by an external pump and exhausted to the atmosphere. The small flow rate allows calculation of fluxes assuming linear relationships between the GHG mixing ratios and chamber lid closure times of a few minutes. We also calibrated the chambers for effective volume (Veff) and show that adsorption of the GHGs on the walls of the chamber caused Veff to be 7% higher than the geometric volume, with the near-surface soil porosity causing another 4% increase in Veff.
关键词： automated non-steady-state chamber system,soil CO2 and CH4 fluxes,laser absorption spectroscopy,cavity ring-down spectrometer
更新于2025-09-16 10:30:52