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Concentric multipass cell enhanced double-pulse laser-induced breakdown spectroscopy for sensitive elemental analysis
摘要： Although double-pulse laser-induced breakdown spectroscopy (DP-LIBS) is regarded as a promising technique in trace element analysis, its limit of detection (LOD) is not sufficient for some applications. The enhancement of spectral signal is the key to further improve the sensitivity of DP-LIBS. To further increase the sensitivity of DP-LIBS, a concentric multipass cell (CMC) enhanced DP-LIBS (CMC-DP-LIBS) technique is proposed for the first time, which makes full use of the energy of reheating laser by multi-reflection in CMC to enhance the spectral signal and lower LOD. 2.3 times signal enhancement of Mn I 403.08 nm line and 2.3 times decrease of LOD of Mn on the surface of zinc bulk compared with traditional orthogonal reheating DP-LIBS were attained. The signal enhancement factor can reach to 3.6 theoretically with the increase of reflectivity and the sizes of mirrors of CMC. This CMC-DP-LIBS provides a new approach to further improve the sensitivity of DP-LIBS and promotes its application in trace element detection.
关键词： Double-pulse,Concentric multipass cell enhancement,Laser-induced breakdown spectroscopy,Detection limit
更新于2025-09-23 15:19:57
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Compact dual-gas sensor for simultaneous measurement of atmospheric methane, and water vapor using a 3.38?μm antimonide-distributed feedback laser diode
摘要： A simple, compact sensor involving a continuous-wave 3.38 mm distributed feedback laser in combination with a novel compact dense-pattern multipass cell was demonstrated for simultaneous measurement of atmospheric methane and water vapor. The calibration-free direct absorption spectroscopy approach was adopted for data generation and processing. Allan deviation analysis indicates that minimum detection limits (1s) of 11.0 ppb for CH4 and 100 ppm for H2O were achieved with a 1-s integration time at an optimum pressure of 50 Torr. Atmospheric environmental mixing ratios of these two gases were recorded and analyzed. This newly developed mid-infrared dual-gas sensor is very suitable for trace gas sensing in weight-limited unmanned aerial vehicle- or balloon-embedded field observations.
关键词： Multipass cell,Laser sensors,Water vapor,Distributed feedback laser,Laser absorption spectroscopy,Methane
更新于2025-09-19 17:13:59
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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) - Adjustable Optical Path Length Compact Spherical Mirrors Multipass Cell Optimized with Genetic Algorithm
摘要： Numerous practical applications, including health and environmental protection, need compact and high sensitivity gas sensors. This work reports an experimental investigation on a compact multipass cell (MPC) designed and optimized with a genetic algorithm (GA) with long, adjustable optical path length (OPL) using only inexpensive spherical mirrors. A four-mirror based MPC with the GA developed here, offers great design flexibility in comparison to a two-mirror solution. As an example, a stable 24 m OPL was reached within only 80 cc volume. Moreover, by changing the mirror positions various stable OPLs can be achieved in a controllable way. The presented MPC consists of four mirrors in a configuration similar to a bow-tie. As a result, the symmetry between the mirrors is broken (mirrors are not parallel to each other) and an astigmatic spot pattern with a high fill factor is obtained. Additionally, the use of the folded optical path geometry causes higher compactness in contrast to an astigmatic mirror-based MPC. Compared to other dense-pattern or folded spherical mirrors MPCs reported previously, longer OPL in the same volume can be obtained. In order to accurately calculate the line-sphere intersection points and reflection angles based on algorithms reported in custom ray tracing software was developed. It also allows to determine the optimal MPC configuration with specified design constraints (mirror diameters, their focal lengths and desirable OPL) by using a GA. To verify the simulation results, we assembled a MPC with four 1” in diameter, 25 mm focal length mirrors mounted in kinematic holders and fixed them to an aluminum base. By changing the angle and distance between the mirrors, different MPC configurations were tested. Several OPLs ranging from 4.5 m to 28 m were achieved with the GA. The longest OPL, with sufficient output beam quality for such mirrors, was 24 m. In order to prove the agreement between the simulation and experiment, a 16 m and 24 m OPL configurations were prepared and the time-of-flight inside the MPC was measured by injecting a 10 ns pulse laser into the cavity. The first pulse (registered at 0 ns delay in Fig. 1c) corresponds to light partially reflected from the optical plate situated near the MPC input, whereas the second one arrives from the output of MPC. By measuring the time delay between both pulses, the actual OPL was calculated. The experimentally obtained OPLs were 16.11 m and 23.88 m, which is in good agreement with the simulated values of 16.1 m and 23.82 m respectively. In conclusion, we present a compact, four-mirror MPC, designed and optimized with a GA in several OPL variants. Then two of them were experimentally verified through time-of-flight measurement inside the MPC.
关键词： optical path length,genetic algorithm,spherical mirrors,multipass cell,gas sensors
更新于2025-09-12 10:27:22