We present E-CAHORS—a compact mid-infrared open-path diode-laser spectrometer designed for the simultaneous measurement of carbon dioxide, methane, and water vapor concentrations in the near-surface atmospheric layer. These measurements, combined with simultaneous data from a three-dimensional anemometer, can be used to determine fluxes using the eddy-covariance method. The instrument utilizes two interband cascade lasers operating at 2.78 µm and 3.24 µm within a novel four-pass M-shaped optical cell, which provides high signal power and long-term field operation without requiring active air sampling. Two detection techniques—tunable diode laser absorption spectroscopy (TDLAS) and a simplified wavelength modulation spectroscopy (sWMS)—were implemented and evaluated. Laboratory calibration demonstrated linear responses for all gases (R2 ≈ 0.999) and detection precisions at 10 Hz of 311 ppb for CO2, 8.87 ppb for CH4, and 788 ppb for H2O. Field tests conducted at a grassland site near Moscow showed strong correlations (R = 0.91 for CO2 and H2O, R = 0.74 for CH4) with commercial LI-COR LI-7200 and LI-7700 analyzers. The TDLAS mode demonstrated lower noise and greater stability under outdoor conditions, while sWMS provided baseline-free spectra but was more sensitive to power fluctuations. E-CAHORS combines high precision, multi-species sensing capability with low power consumption (10 W) and a compact design (4.2 kg).

Reconstruction accuracy is a crucial indicator for assessing the combustion conditions in combustion diagnostics. Existing flame-temperature measurement methods require comparison and verification using simulations, infrared thermal imaging cameras, and thermocouples, which increase measurement complexity and reduce efficiency. This study introduces a method based on tunable diode laser absorption spectroscopy (TDLAS) that utilizes an array sensor to capture specific absorption and radiation spectral signals to measure the combustion field temperature. Active and passive spectral information at different temperatures was obtained through calibration experiments. The temperature field of the K+-doped premixed stable flame was imaged. The difference between the active and passive spectral temperature field images did not exceed 8%, and the maximum relative error compared to the thermocouple measurements did not exceed 6%, demonstrating good reconstruction accuracy. Simultaneous active and passive spectral temperature measurements provide a novel approach for developing high-precision flame measurements and reducing system complexity.

Range-resolved tunable diode laser absorption spectroscopy for humidity sensing

Two near-infrared (NIR) tunable diode laser absorption spectroscopy (TDLAS) diagnostics targeting the cyano radical (CN) near 926 and 1128 nm, respectively, were combined with a multipass absorption spectroscopy ring amplifier to probe varying mixtures of CH4/N2 dilute in Ar over a wide range of post-reflected-shock temperatures (3200–13,000 K) and pressures (0.1–1.7 atm), allowing isolation of CN formation and decomposition reactions. Nine CN absorption features in the red system were probed at scan rates up to 500 kHz to provide quantitative measurements of species number density profiles behind the reflected shock. The data were analyzed using a detailed mechanism and sensitivity analysis to fit four reactions. The rate coefficients for CN+M dissociation, C+CN exchange, and C2+M dissociation are found to be in reasonably good agreement with prior studies at different temperatures in different mixtures. Of these three, only CN dissociation retained good sensitivity for inference from experimental data, while the other two were floated to optimize fits. In contrast, the measured rate for C+N2 exchange, k1=5.65(±0.2)×1014exp(−30,900/T) cm3/(mol⋅s), was found to be up to an order of magnitude faster than that provided by the Gökçen reduced Titan mechanism at high temperatures. When the updated rates are applied to measurements in a pure Titan atmosphere mixture, better agreement is found than predicted by the reaction rates from both Gökçen and Slack.

An ameliorated signal-to-noise enhanced method for tunable diode laser absorption spectroscopy methane detection system using multivariate variational mode decomposition

Neural network optimization algorithms for high-precision TDLAS gas spectroscopic detection.

Time-resolved measurements of N2(A,v) by tunable diode laser absorption spectroscopy in a sub-microsecond pulsed plasma discharge

Tunable diode laser absorption spectroscopy (TDLAS) provides high sensitivity, superior spectral resolution, and a fast response for quantitative gas analysis across applications such as greenhouse gas monitoring, industrial process control, combustion diagnostics, and respiratory medicine. However, the traditional Herriott multipass cell (MPC)─a key optical component in TDLAS─faces challenges due to its large physical size, low mirror utilization efficiency, and strict alignment requirements, limiting portability and field deployment. In this work, we designed and fabricated a compact rectangular-like Herriott cell (RLHC) with a 12.7 m optical path length and physical dimensions of 9.00 × 6.60 × 3.45 cm3 (closed-cell volume ∼58.9 mL), representing the smallest MPC reported for a comparable path length. By transforming a circular (24 mm diameter) beam-spot distribution into an elliptical one (24 mm long axis and 6 mm short axis) and folding the optical axis six times using two high-reflectivity plane mirrors, the RLHC achieves a fill factor of 21.9 cm-2. Integration of a fiber-coupled collimator and an InGaAs photodetector eliminates the need for active optical alignment, resulting in a self-contained sensing module. Using a 1.65 μm distributed feedback laser, the RLHC-based methane sensor achieves a minimum detection limit (MDL) of 38.93 ppbv and a noise-equivalent absorption coefficient of 1.36 × 10-5 Hz-1/2 (approximately an order of magnitude lower than conventional TDLAS systems). Continuous three-day measurements near sewage systems and in ambient air demonstrate strong robustness and long-term stability, underscoring the potential of RLHC-based TDLAS sensors for distributed environmental monitoring, hand-held operation, and large-scale field applications.

Abstract Accurate measurement of gas flow velocities in low-speed flow fields (0~30 m/s) is critical for applications such as vacuum drying, semiconductor manufacturing, and pharmaceutical/food industries. Based on the laser Doppler effect, non-contact high-precision measurement of gas flow velocity can be achieved by capturing the Doppler shift in absorption spectral lines to quantify the gas flow speed. However, under low-speed flow field conditions, weak Doppler shifts (on the order of 10 -5 cm -1 per m/s) and spectral line overlapping pose significant challenges to traditional direct absorption spectroscopy (DAS). To address these issues, this study employs a dual-light-path system based on Tunable Diode Laser Absorption Spectroscopy (TDLAS) and proposes a synchronous iterative fitting algorithm with an L2-norm constraint. This algorithm simultaneously optimizes the baseline and absorption line parameters, effectively eliminating baseline drift and spectral line interference inherent in traditional DAS. Additionally, we analyze the non-uniformity of turbulent flow fields in pipes and model the radial velocity profile using a power-law distribution to elucidate its impact on TDLAS path-averaged velocity measurements. We ensure the reliability of the results by analyzing the effects of turbulence, spectral line distortion caused by stagnant zones, and zero-point deviation during measurements. Using the H 2 O absorption line at 7181.1557 cm -1 , the proposed method measures velocities in the range of 0-25.42 m/s with a relative error of less than 10%. The measurement results exhibit high linearity against reference results on the same conditions, indicating excellent system consistency. This research provides theoretical guidance and technical support for the engineering application of TDLAS in low-speed flow field measurements.

This study presents a novel top-down approach to quantify diffuse methane (CH4) emissions at oil and gas well sites. It uses an unmanned aerial vehicle (UAV) equipped with a scanning–sampling tunable diode laser absorption spectroscopy (TDLAS) CH4 measurement instrument. By integrating the top-down emission rate retrieval algorithm (TERRA) and adopting concentric circular sampling, the method aims to overcome the limitations of traditional ground-based measurements. The UAV system was deployed at 11 oil and gas sites in the Changqing Oilfield. The results show that the average CH4 emission rate detected by the UAV is 1.425 kg/h (excluding non-detected samples), which is larger than the 1.061 kg/h obtained from ground-based onsite direct measurement. This discrepancy may be because the UAV’s scanning–sampling capability can cover a larger area, capturing scattered or hidden diffuse emission sources that might be missed by ground-based onsite direct measurement. The study demonstrates that the UAV-based approach with a scanning–sampling TDLAS CH4 measurement instrument, integrated with the TERRA and concentric circular sampling, is effective in capturing diffuse CH4 emissions at oil and gas well sites, providing a viable method for large-scale and efficient monitoring of such emissions. This approach could provide an effective pathway for large-scale, efficient, and cost-effective monitoring of methane emissions.

Abstract Rice cultivation is a significant source of agricultural methane (CH₄), yet routine quantification still relies heavily on gas chromatography (GC), which limits throughput and field deployment. Here, we evaluated a portable tunable-diode-laser absorption spectroscopy (TDLAS) detector (PMD) as an alternative to GC for measuring CH₄ released from pot-grown rice plants under field conditions. Weekly closed-chamber samples from five cultivars were analyzed in parallel by GC (FID/MS) and the PMD. Standard gas tests showed an excellent linear relationship for the PMD (R 2 = 0.9995), indicating a near-ideal response. Across field samples, GC and PMD were strongly associated (R 2 = 0.9943). Bland–Altman analysis revealed a mean bias (GC − PMD) of 8.55 with 95% limits of agreement − 9.16 to 26.26, and Lin’s concordance correlation coefficient was 0.991, evidencing near-perfect agreement despite a slight systematic offset. A simple calibration with a linear regression eliminated the bias and narrowed the limits of agreement, while preserving the high correlation. Residual analyses suggested a modest influence of CO₂ (but not N₂O) on between-method differences. Taken together, the PMD provides rapid, robust, and labor-efficient CH₄ measurements that closely match GC when a fixed calibration is applied, enabling high-throughput phenotyping of rice genotypes and management practices in both laboratory and field settings. This calibrated, portable approach lowers barriers to large-scale screening for low-emission rice, supporting climate-smart crop improvement.

Fugitive or diffuse methane emissions constitute an important source of damage to the environment, much greater even than CO2 both over a time span of 20 years and over a longer time span of 100. It is therefore of preeminent importance to undertake all the efforts necessary to implement new tools, protocols, and methods that contribute to the identification and measurement of these emissions to implement site-specific actions of mitigation, repair, and conscious management of the emitting plants. Among the remote sensing and leak detection technologies currently used, the tunable diode laser absorption spectroscopy (TDLAS) method plays a relevant role. Thanks to the study and implementation of increasingly high-performance sensors to be equipped on drones, this method is strongly promoted in the unmanned aerial vehicle sector. However, as often happens, the operational performance of a measurement method must be associated with measurement errors, which must be foreseen (where possible), and certainly detailed and corrected. The purpose of this article is to describe the procedure for identifying and processing "false-positive" values recorded by the payload during a survey flight for the measurement of methane concentrations in airborne matrix, with a TDLAS sensor. The methodology contained in this article is based on the study of scientific evidence referable to previous in-depth experiences on false positives and largely on the direct experience gained by the project team of the TALSEF laboratory (University of Bari, Italy) during numerous measurement campaigns in landfills, oil and gas sites, and cattle stables.

A mathematical model was established to describe the sublimation and diffusion of water molecules and their adsorption onto cold traps. This model was used to analyze the combined influence mechanisms of sublimation temperature and ambient pressure on the vapor deposition process of water ice. Tunable Diode Laser Absorption Spectroscopy (TDLAS) was employed to provide real-time feedback on water vapor concentration within the experimental apparatus. Based on this feedback, the sublimation temperature was dynamically adjusted to maintain the concentration dynamically stabilized around the target value. A dedicated apparatus for generating controlled water vapor flow fields and detecting concentration was constructed. The accuracy of both the mathematical model and Finite Element Analysis (FEA) simulations was verified through comparative experiments. Laser triangulation was utilized as a method to detect the thickness of the adsorbed ice film on the sample surface. Leveraging this technique, a water vapor deposition and adsorption verification system was developed. This system was used to test the differences in water adsorption performance across various materials and to measure the correlation between the thickness of the adsorbed/deposited ice film on the samples and both deposition time and sublimation temperature.

Abstract The synergy between voltage waveform tailoring and structured electrodes is investigated in a radio -frequency atmospheric-pressure microplasma jet operated in helium with a 0.1% oxygen admixture. The device incorporates rectangular trenches in both electrodes and is driven by ‘Peaks’ and ‘Valleys’ waveforms synthesized from four harmonics (base frequency f b = 13.56 MHz, V pp = 500 V, and P = 1.2 W). Two-dimensional plasma fluid simulations, together with spatially and temporally resolved optical diagnostics (phase-resolved optical emission spectroscopy and tunable diode laser absorption spectroscopy), are used to demonstrate that the combination of asymmetric voltage waveforms with electrode structuring results in the strong spatial localization of electron power absorption and radical generation. This synergy leads to a single pronounced maximum inside a trench at either the powered or grounded electrode, depending on the applied waveform, unlike a symmetric excitation, which produces a spatially symmetric enhancement at both electrodes. This effect is attributed to the interplay between waveform-induced sheath dynamics and geometric focusing provided by the trenches, enabling electrically reversible and selective enhancement of electron power absorption at a chosen location.

Summary In this study, we propose a systematic method for optimizing the scanning strategy of pan-tilt tunable diode laser absorption spectroscopy (TDLAS) detection devices to enhance inspection efficiency. Gas leakage scenarios are identified and then simulated using computational fluid dynamics (CFD) to predict concentration distributions across the monitoring area. A multicondition data extraction model is developed to process and retrieve the CFD data. The optimization goal is framed as the minimum cumulative detection time considering scenario probabilities (MCDT-SP), with an enhanced particle swarm optimization (PSO) solution algorithm used to simultaneously optimize scanning points and sampling durations. The approach is demonstrated through a case study at a natural gas liquefaction plant, where results show significant improvements in detection efficiency, including reduced scanning points and faster leak detection. This method holds significant potential for application in industrial scenarios utilizing TDLAS technology for detection and is expected to provide actionable insights and effective support for the development of inspection strategies in the oil and gas industry.

We present a tunable diode-laser absorption spectroscopy (TDLAS) system operating at 1.5711 µm for CO2 gas concentration measurements. The system can operate in either a traditional direct-mode (dTDLAS) sawtooth wavelength scan or a recently demonstrated wavelength-toggled single laser differential-absorption lidar (WTSL-DIAL) mode using precompensated current pulses. The use of such precompensated pulses offsets the slow thermal constants of the diode laser, leading to fast toggling between ON and OFF-resonance wavelengths. A short measurement time is indeed pivotal for atmospheric sensing, where ambient factors, such as turbulence or mechanical vibrations, would otherwise deteriorate sensitivity, precision and accuracy. Having a system able to operate in both modes allows us to benchmark the novel experimental procedure against the well-established dTDLAS method. The theory behind the new WTSL-DIAL method is also expanded to include the periodicity of the current modulation, fundamental for the calculation of the OFF-resonance wavelength. A two-detector scheme is chosen to suppress the influence of laser intensity fluctuations in time (1/f noise), and its performance is eventually benchmarked against a one-detector approach. The main difference between dTDLAS and WTSL-DIAL, in terms of signal processing, lies in the fact that while the former requires time-consuming data processing, which limits the maximum update rate of the instrument, the latter allows for computationally simpler and faster concentration readings. To compare other performance metrics, the update rate was kept at 2 kHz for both methods. To analyze the dTDLAS data, a four-parameter Lorentzian fit was performed, where the fitting function comprised the six main neighboring absorption lines centered around 1.5711 µm. Similarly, the spectral overlap between the same lines was considered when analyzing the WTSL-DIAL data in real time. Our investigation shows that, for the studied time intervals, the WTSL-DIAL approach is 3.65 ± 0.04 times more precise; however, the dTDLAS-derived CO2 concentration measurements are less subject to systematic errors, in particular pressure-induced ones. The experimental results are accompanied by a thorough explanation and discussion of the models used, as well as their advantages and limitations.

Cross-interference from overlapping absorption spectra of different gases significantly limits the precision and stability of gas concentration detection using traditional absorption spectroscopy. This study proposes a novel model integrating the global search capability of the genetic algorithm (GA), the local optimization ability of the heterogeneous improved dynamic multiswarm particle swarm optimization (HIDMS-PSO), and the nonlinear modeling of the backpropagation neural network (BPNN), termed the GA-HIDMS-PSO-BPNN model, to solve the cross-interference problem in tunable diode laser absorption spectroscopy (TDLAS) for a dual-gas sensor detecting CH4 and CO. In a 1500 s stability test, the model demonstrates reliable performance, achieving standard deviations of 24.7753 ppm at 5000 ppm of CH4 and 0.3075 ppm at 30 ppm of CO. These results verify the effectiveness of the model in improving the accuracy and reliability of the dual-gas sensor. It provides a robust approach for maintaining high-precision concentration measurements under cross-interference conditions and offers an efficient solution for multicomponent gas analysis.

The filament arc driven plasma, cesiated surface conversion H - ion source used at the Los Alamos Neutron Science Center (LANSCE) has a long legacy of providing reliable beam to the LANSCE user program. Despite the long history of beam delivery, there remains valuable opportunity for fundamental diagnostic studies, and subsequent operational improvements of the LANSCE H - ion source based on these diagnostics. The LANSCE H - Ion Source Laser Diagnostic Stand (HLDS) was built to study these fundamental diagnostics. HLDS is currently capable of measuring cesium density/temperature via Tunable Diode Laser Absorption Spectroscopy (TDLAS), and plasma properties related to the H α Balmer line via Optical Emission Spectroscopy (OES) and TDLAS. An update will be given on measurements taken using these diagnostic tools. In particular, detailed focus will be given on how results from the Cs TDLAS diagnostic was used to mitigate arc and converter transients due to Cs instabilities, to study hastening the Cs conditioning process, and a first look at continuous Cs density monitoring during Cs conditioning and operation. Finally, a first look and interpretation of the commissioned data taken of the H α Balmer line via OES and TDLAS will be discussed.

Enhancement mechanism and optimization analysis of resonant excitation Laser-induced Breakdown Spectroscopy (LIBS-RE) in gaseous ammonia element detection.

An airborne CH4 sensor with temperature compensation based on a miniature optical structure for natural gas pipeline leakage analysis.