Ultrashort Pulse Generation in Ce:LiCAF Ultraviolet Laser

Transient cavity method used to generate ultrashort laser pulses in dye lasers is extended to a solid-state gain medium. Numerical simulations are performed to investigate the spectro-temporal evolution of broadband ultraviolet (UV) laser emission from Ce3+-doped LiCaAlF6 (Ce:LiCAF), which is represented as a system of two homogeneous broadened singlet states. By solving the rate equations extended to multiple wavelengths, the appropriate cavity length and Q-factor for optimal photon cavity decay time and pumping energy that will generate resonator transients is determined. Formation of resonator transients could generate picosecond UV laser pulses from a Ce:LiCAF crystal pumped by the fourth harmonics (266 nm) of a Nd:YAG laser. Numerical simulations indicate that a 1-mol% Ce3+-doped LiCAF crystal that is 1-mm long can generate a single picosecond pulse. This is accomplished by using a low Q (output coupler reflectivity of 10%), short cavity (cavity length of 2 mm) laser oscillator. Ultrashort pulses can also be generated using other rare earth-doped fluoride laser materials using this technique

Elastic Scattering Time–Gated Multi–Static Lidar Scheme for Mapping and Identifying Contaminated Atmospheric Droplets

Numerical simulations are performed to determine the angular dependence of the MIe scattering cross-section intensities of pure water droplets and pollutants such as contaminated water droplets and black carbon as a function of the wavelength of the incident laser light, complex refractive index, and size of the scatterer. Our results show distinct scattering features when varying the various scattering parameters, thereby allowing the identification of the scattering particle with specific application to the identification of atmospheric pollutants including black carbon. Regardless of the type of scatterer, the scattering intensity is nearly uniform with a slight preference for forward scattering when the size of the particle is within 20% of the incident laser’s wavelength. The scattering patterns start to exhibit distinguishable features when the size parameter equals 1.77, corresponding to an incident laser wavelength of 0.355 μm and a particle radius of 0.1 μm. The patterns then become increasingly unique as the size parameter increases. Based on these calculations, we propose a time-gated lidar scheme consisting of multiple detectors that can rotate through a telescopic angle and be placed equidistantly around the scattering particles to collect the backscattered light and a commercially available Q-switched laser system emitting at tunable laser wavelengths. By using a pulsed laser with 10-ns pulse duration, our scheme could distinguish scattering centers that are at least 3 m apart. Our scheme called MIe Scattering Time-gated multi-Static LIDAR (MISTS–LIDAR) would be capable of identifying the type of atmospheric pollutant and mapping its location with a spatial resolution of a few meters.Mui L.V., Hung T.N., Shinohara K., et al. Elastic Scattering Time–Gated Multi–Static Lidar Scheme for Mapping and Identifying Contaminated Atmospheric Droplets. Applied Sciences (Switzerland) 13, 172 (2023); https://doi.org/10.3390/app13010172

Impact assessment of biomass burning in Southeast Asia to 2019 annual average PM2.5 concentration in Thailand using atmospheric chemical transport model

Agricultural residues burning as a means of land preparation commonly practiced in many Southeast Asian countries causes significant deterioration of ambient air quality and public health. In this study, WRF-CMAQ Atmospheric Chemical Transport Model was used to conduct a year-round simulation (1 January - 31 December 2019) of PM2.5 spatio-temporal variation over Southeast Asia. The model utilized the Fire emission Inventory from NCAR (FINNv1.5) from National Center for Atmospheric Research (NCAR) as a biomass burning emission input. The model performance was evaluated by comparing simulated values with observed values from monitoring stations in nine major cities. The model shows acceptable performance reproducing the PM2.5 concentration with 14.9% normalized mean bias (NMB) and correlation coefficient of 0.89. After that, the simulation was conducted again with emission from FINNv1.5 turned off. The results from FINNv1.5 on and off cases were then compared to evaluate contribution of biomass burning to PM2.5 concentration in two major cities of Thailand: Bangkok and Chiang Mai. The comparison shows that biomass burning contributes to 49.1% and 13.1% of PM2.5 annual average concentration in Chiang Mai and Bangkok respectively with highest month being April for Chiang Mai (70.7% contribution) and March for Bangkok (35.5% contribution)

Comprehensive Analysis of Organic Micropollutants in Fine Particulate Matter in Hanoi Metropolitan Area, Vietnam

Rapid urbanization has led to increased environmental pollution in Vietnam, especially air pollution issues. In this study, we used gas chromatography-mass spectrometry with an automated identification and quantification system database to detect and quantitate compounds in atmospheric fine particulate matter (PM2.5). A total of 288 compounds classified in 19 pollutant categories based on their origins were detected in PM2.5 samples collected in three areas of Hanoi during winter. The total content of substances detected ranged from 41.08 to 795.00 ng.m−3. The characteristics and concentrations of organic pollutants differed among the industrial, urban, and agricultural sampling areas, with average concentrations of 179.00, 112.10, and 529.40 ng.m−3, respectively. In this comprehensive study on trace organic compounds conducted with samples collected at three sites, we investigating the basic impact of three main factors on the environment. This study contributes to the literature by providing a data set on the content of trace organic substances in the air at the study site

Comprehensive Analysis of Organic Micropollutants in Fine Particulate Matter in Hanoi Metropolitan Area, Vietnam

Rapid urbanization has led to increased environmental pollution in Vietnam, especially air pollution issues. In this study, we used gas chromatography-mass spectrometry with an automated identification and quantification system database to detect and quantitate compounds in atmospheric fine particulate matter (PM2.5). A total of 288 compounds classified in 19 pollutant categories based on their origins were detected in PM2.5 samples collected in three areas of Hanoi during winter. The total content of substances detected ranged from 41.08 to 795.00 ng.m−3. The characteristics and concentrations of organic pollutants differed among the industrial, urban, and agricultural sampling areas, with average concentrations of 179.00, 112.10, and 529.40 ng.m−3, respectively. In this comprehensive study on trace organic compounds conducted with samples collected at three sites, we investigating the basic impact of three main factors on the environment. This study contributes to the literature by providing a data set on the content of trace organic substances in the air at the study site

Elastic Scattering Time–Gated Multi–Static Lidar Scheme for Mapping and Identifying Contaminated Atmospheric Droplets

Numerical simulations are performed to determine the angular dependence of the MIe scattering cross-section intensities of pure water droplets and pollutants such as contaminated water droplets and black carbon as a function of the wavelength of the incident laser light, complex refractive index, and size of the scatterer. Our results show distinct scattering features when varying the various scattering parameters, thereby allowing the identification of the scattering particle with specific application to the identification of atmospheric pollutants including black carbon. Regardless of the type of scatterer, the scattering intensity is nearly uniform with a slight preference for forward scattering when the size of the particle is within 20% of the incident laser’s wavelength. The scattering patterns start to exhibit distinguishable features when the size parameter equals 1.77, corresponding to an incident laser wavelength of 0.355 μm and a particle radius of 0.1 μm. The patterns then become increasingly unique as the size parameter increases. Based on these calculations, we propose a time-gated lidar scheme consisting of multiple detectors that can rotate through a telescopic angle and be placed equidistantly around the scattering particles to collect the backscattered light and a commercially available Q-switched laser system emitting at tunable laser wavelengths. By using a pulsed laser with 10-ns pulse duration, our scheme could distinguish scattering centers that are at least 3 m apart. Our scheme called MIe Scattering Time-gated multi-Static LIDAR (MISTS–LIDAR) would be capable of identifying the type of atmospheric pollutant and mapping its location with a spatial resolution of a few meters