Simultaneous detection of atmospheric CO and CH4 based on TDLAS using a single 2.3 μm DFB laser.

Laser sensors for energy systems and process industries: Perspectives and directions

The development of innovative methods for optimizing carbon nanotube-based gas sensors for rapid and sensitive detection of ammonia remains challenging. Here, [email protected]/TfmpoPcCo hybrid with a uniform 3-D network were prepared by tightly combining tetra-β-trifluoromethylphenoxyphthalocyanine cobalt (TfmpoPcCo) on the surface of [email protected] through π-π interactions and used to construct NH3 sensor, while the [email protected] were obtained by in-situ polymerization of PPy onto the side wall of MCNT. TfmpoPcCo not only adsorbs on the [email protected] side wall due to its structure advantages, but also acts as a sensor accelerator. [email protected]/TfmpoPcCo sensor show higher NH3 sensing performance than the MCNT, PPy and TfmpoPcCo under same operating conditions, especially in ultrafast response/recovery time (11.7 s/91.8 s to 50 ppm NH3) with low limit-of-detection of 11 ppb at room temperature (20 °C) and excellent gas selectivity. In addition, the [email protected]/TfmpoPcCo sensor preserve superior gas response (26.2% to 50 ppm NH3) as well as outstanding stability over 60 days and humidity resistance. The excellent NH3 sensing properties are attributed to the excellent gas selectivity of TfmpoPcCo, the unique redox characteristics of PPy to ammonia (NH3), and the good electron transport ability and stability of MCNT. The synergistic optimization strategy of ternary materials is of great significance towards the exploration and construction of ideal materials for gas sensor in the future. 

Ultrafast NH3 gas sensor based on phthalocyanine-optimized non-covalent hybrid of carbon nanotubes with pyrrole†

We developed a type of toroidal multi-pass cell with multi-layer patterns based on the off-axis model. The effective path length of the original toroidal multi-pass cell is extended several roundtrips in comparison with the single-layer pattern, since the inner surface of the toroidal multi-pass cell is more efficiently utilized. The light pattern has been achieved by using the simple ring surface, which is easy to fabricate. The exact analytical equations for the design of the toroidal multi-pass cell were derived based on analytical vector calculations. A series of numerical ray tracing simulations is presented, and the maximum theoretical optical path length that can be reached is 30 m with a setup of 5 cm column radius. Furthermore, two practical spot patterns are demonstrated with a path length of 8.3 m for a two-layer pattern and 10 m for a three-layer pattern, with respective effective volumes of 63 mL and 94 mL. Furthermore, the fringe effect is substantially reduced to less than 0.5% by the usage of our designed mask.

/pdf/implementation-of-the-toroidal-absorption-cell-with-multi-24wqlzh5tb.pdf

Implementation of the toroidal absorption cell with multi-layer patterns by a single ring surface.

A palm-sized laser spectrometer has been developed for detecting trace gases based on tunable diode laser absorption spectroscopy (TDLAS) in combination with a novel double-layer toroidal cell. With the beneﬁt of a home-made electronic system and compact optical design, the physical dimension of the sensor is minimized into 24×15×16 cm3. A toroidal absorption cell, with 84 reflections in 2 layers for an effective optical path length of 8.35 m, was used to enhance the absorption signals of gaseous species. A home-made electronic system was designed for implementing distributed feedback (DFB) diode laser controller, analog lock-in amplifier, data acquisition and communication. Calibration-free scanned wavelength modulation spectroscopy was employed to determine the concentration of the gas and reduce the random ﬂuctuations from electronical noise and mechanical vibration. The measurement of CH4 in ambient air was demonstrated using a DFB laser at 1.653 μm. The rise time and fall time for renewing the gas mixture are approximately 16 s and 14 s, respectively. Vibration and temperature tests have been carried out for verifying the performance of the spectrometer, and standard deviations of 0.38 ppm and 0.11 ppm for 20 ppm CH4 at different vibration frequencies and temperatures, respectively, have been determined. According to the Allan deviation analysis, the minimum detection limit for CH4 can reach 22 ppb at an integration time of 57.8 s. Continuous measurement of atmospheric CH4 for two days validated the feasibility and robustness of our laser spectrometer, providing a promising laser spectral sensor for deploying in unmanned aerial vehicles or mobile robots.

/pdf/palm-sized-laser-spectrometer-with-high-robustness-and-3vu1gfmd20.pdf

Palm-Sized Laser Spectrometer with High Robustness and Sensitivity for Trace Gas Detection Using a Novel Double-Layer Toroidal Cell.

A portable sensor for in-situ measurement of ammonia based on near-infrared laser absorption spectroscopy

Detection of RC Spalling Damage and Quantification of Its Key Properties from 3D Point Cloud

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A portable sensor for in-situ measurement of ammonia based on near-infrared laser absorption spectroscopy

Detection of RC Spalling Damage and Quantification of Its Key Properties from 3D Point Cloud