Quantity Determintation And Traceability For Super-resolution Mid-infrared Laser Absorption Spectroscopy

Super-resolution spectroscopy is essential for the understanding of molecular fine structures, excited state population, distribution function of given energy states, and remote sensing applications. We addressed several key measures for achieving high performances of sprectral resolution and absorbance precision in a mid-infrared modulated laser spectrometer with a distributed feedback interband cascade laser, including linearization of laser scanning, suppression or deduction of optical fringe interferences, and internal calibration for baseline problems and nonlinear response of the photodiode used in the system. The performances of our modified spectrometer were verified with the spectral resolution in the order of 10$^{-6}$ cm$^{-1}$ (\~hundreds kHz) and absorbance uncertainty in the order of 10$^{-3}$. We provided a detailed error analysis with the uncertainty model of GUM, i.e. Guide to the expression of uncertainty in measurement. Further, we ensured the traceability of the spectrometer by linking a practical calibration reference standard. We measured the fundamental absorption of several organic molecules, e.g. dimethyl sulfide (CH$_{3}$)$_{2}$S), methyl mercaptan (CH$_{3}$SH) with our modified spectrometer. The recorded spectra were demonstrated to be similar to that in the Pacific Northwest National Laboratory (PNNL) database. These data have been used in our remote sensing applications

TIME-RESOLVED MEASUREMENT OF THE C2 1AΠu STATE POPULATION FOLLOWING PHOTODISSOCIATION OF THE S1 STATE OF ACETYLENE USING FREQUENCY-MODULATION SPECTROSCOPY

The excited-state population of the C$_2$ $^1APi_u$ state produced in photolysis of S$_1$ acetylene was investigated. The pulsed UV laser (216.5 nm) excites acetylene into $J=8$ $e$-symmetry level of the S$_1$ $3^4$ level, and subsequently dissociates the S$_1$ acetylene into C$_2$ fragments. A frequency-modulated near-infrared probe laser beam is used to detect the C$_2$ population in the $^1APi_u$ state. The sensitivity and the fast response of the experimental setup has been verified by I$_2$ excited state measurements. The setup will be used to record the C$_2$ $A-X$ transitions, which are fitted with a Voigt function. The derived lineshape and line intensities will be analyzed, and we will use the information to calculate the $A$ state populations of C$_2$ and map the populations with time-resolution following the photolysis

CBLab: Supporting the Training of Large-scale Traffic Control Policies with Scalable Traffic Simulation

Traffic simulation provides interactive data for the optimization of traffic control policies. However, existing traffic simulators are limited by their lack of scalability and shortage in input data, which prevents them from generating interactive data from traffic simulation in the scenarios of real large-scale city road networks. In this paper, we present \textbf{C}ity \textbf{B}rain \textbf{Lab}, a toolkit for scalable traffic simulation. CBLab consists of three components: CBEngine, CBData, and CBScenario. CBEngine is a highly efficient simulator supporting large-scale traffic simulation. CBData includes a traffic dataset with road network data of 100 cities all around the world. We also develop a pipeline to conduct a one-click transformation from raw road networks to input data of our traffic simulation. Combining CBEngine and CBData allows researchers to run scalable traffic simulations in the road network of real large-scale cities. Based on that, CBScenario implements an interactive environment and a benchmark for two scenarios of traffic control policies respectively, with which traffic control policies adaptable for large-scale urban traffic can be trained and tuned. To the best of our knowledge, CBLab is the first infrastructure supporting traffic control policy optimization in large-scale urban scenarios. CBLab has supported the City Brain Challenge @ KDD CUP 2021. The project is available on GitHub:~\url{https://github.com/CityBrainLab/CityBrainLab.git}.Comment: Accepted by KDD2023 (Applied Data Science Track

Detection of Atmospheric Methyl Mercaptan Using Wavelength Modulation Spectroscopy with Multicomponent Spectral Fitting

Detection of methyl mercaptan (CH3SH) is essential for environmental atmosphere assessment and exhaled-breath analysis. This paper presents a sensitive CH3SH sensor based on wavelength modulation spectroscopy (WMS) with a mid-infrared distributed feedback interband cascade laser (DFB-ICL). Multicomponent spectral fitting was used not only to enhance the sensitivity of the sensor but also to determine the concentration of interferents (atmospheric water and methane). The results showed that the uncertainties in the measurement of CH3SH, H2O, and CH4 were less than 1.2%, 1.7% and 2.0%, respectively, with an integration time of 10 s. The CH3SH detection limit was as low as 7.1 ppb with an integration time of 295 s. Overall, the reported sensor, boasting the merits of high sensitivity, can be used for atmospheric methyl mercaptan detection, as well as multiple components detection of methyl mercaptan, water, and methane, simultaneously

One-colour (∼220 nm) resonance-enhanced (S1 − S0) multi-photon dissociation of acetylene: probe of the C2 A1 Πu − X1 Σ+ g band by frequency-modulation spectroscopy

In a recent paper, we demonstrated that one-colour (∼220 nm), resonance-enhanced (S (Formula presented.) S (Formula presented.)), photodissociation of acetylene generates strong (Formula presented.) Swan band ((Formula presented.)) and (Formula presented.) Deslandres-d'Azambuja band ((Formula presented.)) fluorescence, and long-lived (>3 µs) fluorescence from an electronically-excited (Formula presented.) H (Formula presented.) species. It was not known whether the (Formula presented.) and (Formula presented.) states are also directly populated in this process. In this work, multiple vibration-rotation transitions between the (Formula presented.) -state v = 2 and the X-state v = 0 level are examined by time-resolved frequency-modulation (FM) spectroscopy. The photolysis laser wavelength is tuned into resonance at the one-photon level with S (Formula presented.) S (Formula presented.) transitions that populate individual rotational levels of the S (Formula presented.) -conformer (Formula presented.), (Formula presented.), and (Formula presented.) vibrational states. By comparing the phase of the FM signals from the (Formula presented.) transitions with that from the Rb D (Formula presented.) -line absorption transition, we determine that, for all of the probed A−X transitions, the X-state level is more populated than the A-state level. We propose that the acetylene S (Formula presented.) level is excited by the second photon to an acetylene dissociation precursor state, which undergoes sequential C-H bond-breaking to produce the (Formula presented.) state. The dissociation precursor is assigned as the (Formula presented.) valence state, which correlates to a doubly-excited configuration, (Formula presented.), at linear geometry. Based on the rotational distributions of the (Formula presented.) -state fragments, we believe that at least one of the transition states involved in the photolysis via S (Formula presented.) has a larger CC-H bend-angle for the departing H-atom than that involved in the S (Formula presented.) and (Formula presented.) photolysis.SCOPUS: ar.jinfo:eu-repo/semantics/publishe

Standoff Chemical Detection Using Laser Absorption Spectroscopy: A Review

Remote chemical detection in the atmosphere or some specific space has always been of great interest in many applications for environmental protection and safety. Laser absorption spectroscopy (LAS) is a highly desirable technology, benefiting from high measurement sensitivity, improved spectral selectivity or resolution, fast response and capability of good spatial resolution, multi-species and standoff detection with a non-cooperative target. Numerous LAS-based standoff detection techniques have seen rapid development recently and are reviewed herein, including differential absorption LiDAR, tunable laser absorption spectroscopy, laser photoacoustic spectroscopy, dual comb spectroscopy, laser heterodyne radiometry and active coherent laser absorption spectroscopy. An update of the current status of these various methods is presented, covering their principles, system compositions, features, developments and applications for standoff chemical detection over the last decade. In addition, a performance comparison together with the challenges and opportunities analysis is presented that describes the broad LAS-based techniques within the framework of remote sensing research and their directions of development for meeting potential practical use

A Self-Assembly of Single Layer of Co Nanorods to Reveal the Magnetostatic Interaction Mechanism

In this work, we report a self-assembly method to fabricate a single layer of Co nanorods to study their magnetostatic interaction behavior. The Co nanorods with cambered and flat tips were synthesized by using a solvothermal route and an alcohol–thermal method, respectively. Both of them represent hard magnetic features. Co nanorods with cambered tips have an average diameter of 10 nm and length of 100 nm with coercivity of 6.4 kOe, and flat-tip nanorods with a 30 nm diameter and 100 nm length exhibit a coercivity of 4.9 kOe. They are further assembled on the surface of water in assistance of surfactants. The results demonstrate that the assembly type is dependent on the magnetic induction lines direction. For Co nanorods with flat tips, most of magnetic induction lines are parallel to the length direction, leading to an assembly that is tip to tip. For Co nanorods with cambered tips, they are prone to holding together side by side for their random magnetic induction lines. Under an applied field, the Co nanorods with flat tips can be further aligned into a single layer of Co nanorods. Our work gives a possible mechanism for the magnetic interaction of Co nanorods and provides a method to study their magnetic behavior

Mid-Infrared Tunable Laser-Based Broadband Fingerprint Absorption Spectroscopy for Trace Gas Sensing: A Review

The vast majority of gaseous chemical substances exhibit fundamental rovibrational absorption bands in the mid-infrared spectral region (2.5–25 μm), and the absorption of light by these fundamental bands provides a nearly universal means for their detection. A main feature of optical techniques is the non-intrusive in situ detection of trace gases. We reviewed primarily mid-infrared tunable laser-based broadband absorption spectroscopy for trace gas detection, focusing on 2008–2018. The scope of this paper is to discuss recent developments of system configuration, tunable lasers, detectors, broadband spectroscopic techniques, and their applications for sensitive, selective, and quantitative trace gas detection