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A bending vector sensor based on a ring laser and super-mode interference in a seven-core fiber (SCF) is presented. The super-mode interference is originated via a Mach–Zehnder interferometer constructed with an SCF spliced between two single-mode fibers. The interference modulates the cavity laser losses of an erbium-doped ring cavity laser. As the interferometer structure is bent, the interference pattern suffers a wavelength shift, reconfiguring the cavity losses and tuning the laser emission. When the interferometer structure is bent in different directions, the cavity losses are rearranged differently depending on the direction, resulting in different laser outputs. Relating the laser output emission to the bending position, a bending vector sensor is obtained. The identification of the bending direction is related to the peak intensity, whereas the curvature magnitude to the wavelength peak. • Demonstration of a laser bending sensor based on interference in a seven-core fiber. • Determination of four bending directions with behavior of more than those directions. • Favorable temporal stability with minimal fluctuations in wavelength and intensity. [ABSTRACT FROM AUTHOR]

• A highly sensitive Airborne Laser Photo-Acoustic CH 4 Gas Analyzer (7.7 μm) is developed. • A resonant differential photo-acoustic detector and a sealed-off gas-filled Ref -cell was used. • The minimum measured background signal of the PA sensor is n min ≈ (26.6 ± 8.4) ppb CH 4 (at a bandwidth of 20 Hz). • The value of normalized noise equivalent absorption is (NNEA) = 8.22 × 10–10 cm−1·W/Hz1/2. A compact laser photo-acoustic (PA) methane sensor based on a quantum-cascade laser (∼7.7 μm; 1750 Hz; 25 mW), a resonant differential photo-acoustic detector (PAD), and a sealed-off gas-filled PA Ref -cell has been developed. Normalization of the absorption signals in the PAD is carried out according to the absorption signals in the gas-filled PA Ref -cell, which significantly reduces the measurement errors of the methane concentration in the case of instability of the laser emission wavelength. The minimum measured background signal of the PA sensor (using high purity nitrogen) is n min ≈ (26.6 ± 8.4) ppb CH 4 (at a bandwidth of 20 Hz), the value of normalized noise equivalent absorption (NNEA) = 8.22 × 10–10 cm−1·W/Hz1/2. A comparison of various research groups results with mid-IR PA gas analyzers is carried out. The developed PA methane sensor is adapted for placement on the UAV's board. Device has dimensions of 315 × 165 × 110 mm, weight ∼3.1 kg, power supply from an external source (9...60 VDC), power consumption ∼20 VA. [ABSTRACT FROM AUTHOR]

• Open-path standoff gas detection for atmospheric NO using WMS-2f/1f method and QCL. • Adaptive Kalman filter improves 33% in detection accuracy with a response time of 7 s. • Dynamic response, accuracy, sensitivity, and detection limit are evaluated in the laboratory. • Temporal evolution of NO in the atmosphere is measured by field experiments. Nitric oxide (NO) is one of the primary air pollutants, and open optical path detection of NO holds immense significance in safeguarding the ecological environment and human health. In this paper, a high precision and high sensitivity NO open optical path sensor based on mid-infrared laser absorption spectroscopy technology is developed. The average gas concentration inversion of the NO path is achieved by collecting the backscattered light from the cooperative target. The gas measurement deploys a wavelength modulation method to remove the effects from light intensity variations. Furthermore, a Kalman filter and a temperature–pressure sensor optimization software algorithm were utilized to reduce the effects of temperature–pressure variations during the measurement process, leading to a 33% improvement in detection accuracy. The performance of the sensor was evaluated in the laboratory environment in terms of accuracy, sensitivity, and detection limit. The atmospheric NO concentration was also measured under varying time periods and weather conditions in the field environment, thus laying a strong foundation for studying the spatial and temporal evolution of NO in the atmosphere. [ABSTRACT FROM AUTHOR]

• A high-sensitive multi-pass photoacoustic spectroscopy sensor is developed for hydrogen sulfide. • With the enhancement of effective laser power in the multi-pass PA cell, the 2 f -signal of the target H 2 S line has a ∼ 8 times improvement. • The minimum detection concentration of the system can reach 0.13 ppm with a 1-minute averaging time. A high-sensitive tunable diode laser sensor based on photoacoustic spectroscopy and multi-pass absorption spectroscopy is developed for hydrogen sulfide (H 2 S) detection using a target absorption line at 6287.005 cm−1. Two spherical concave mirrors are utilized as the reflectors to make the laser beam pass through the photoacoustic cell for 24 times. The wavelength modulation spectroscopy technique with second harmonic detection (WMS- 2f) method is employed to reduce external interference and increase the detection sensitivity. With the enhancement of the effective laser power in the multi-pass PA cell, the photoacoustic 2f signal of the target H 2 S absorption line has a ∼ 8 times improvement compared to the sensor system without multi-pass cell. Based on the results of Allan variance analysis, the minimum detection concentration of the system could reach 0.68 ppm with a 10-s average time and it can be further lowered down to ∼ 0.1 ppm when a 1-minute averaging time is used. The linear responsivity of the multi-pass PA spectroscopy sensor is estimated to be ∼ 0.00112 mV/ppm by linear fitting for a continuous flow gas measurement results. The excellent performance validates the potential of the sensor for field application. [ABSTRACT FROM AUTHOR]

When using single-photon detector array lidar to detect ships in a foggy environment, the multiple scattering between laser and sea fog, sea surface and ships leads to a large number of fake images in the reconstructed depth images, which seriously limits the ability to detect and recognize ships. Here, we propose a three-dimensional imaging algorithm suitable for ships in fog with a single-photon detector array lidar. This algorithm can eliminate fake images caused by multiple reflections of the sea surface in a foggy environment. Firstly, the algorithm uses a dual-Gamma estimation algorithm to eliminate the influence of non-signal photons, and uses a pulse-like selection algorithm to accurately extract the target echo waveform. Secondly, based on the characteristics of the target echo, the principal component analysis (PCA) and K-means algorithm are used to cluster the features of the separated echo signals. Finally, the result of feature classification is used to achieve efficient fake images removal. We show that the proposed algorithm can more accurately reconstruct the depth image of a ship with a distance of 1.72 km in fog environment. Compared with the traditional algorithms, the proposed algorithm can suppress the sea surface reflection while retaining the most target contour. It has been successfully demonstrated for small ships at different distances. This research is expected to improve the detection and recognition ability of single-photon detector array lidar for small targets in complex scenes. [ABSTRACT FROM AUTHOR]

A fiber laser curvature sensor based on dual-wavelength gain competitive intensity difference demodulation is proposed and experimentally demonstrated. Here a linear cavity dual-wavelength erbium-doped fiber laser (DWEDFL) is build with two filter components i.e. fiber Bragg gratings (FBG) with very close center wavelengths. Since the dual wavelengths are sharing the same gain medium erbium-doped fiber (EDF), gain competition mechanism is formed with sensitive feature to external measurand curvature. Besides, the curvature information is demodulated by subtracting the power of the dual wavelengths. Experimental results show a total sensitivity as high as -57.22 dB/m−1. Our scheme not only improves the measuring sensitivity, but also eliminates the effects of source power jitter and external disturbances for example temperature shift since they do almost the same impact on the dual wavelengths. [ABSTRACT FROM AUTHOR]

Schematic representation of the proposed sensing system based on laser-scribed graphene modified molecularly imprinted polymer for Bisphenol A. • Simple, mask-free, low-cost sensor based on LSG technology combined to MIPs for BPA determination. • Fabrication of LSG electrodes by CO 2 laser with low resistivity 58 Ω/square on flexible polyimide sheet. • Sensitive electrochemical detection of BPA with a LOD of 8 nM. • Accurate detection of BPA in tap, mineral water and in plastic samples. Bisphenol A (BPA) is a toxic chemical used by industries for production of containers for storage of food and beverages leading to possible health risks. In this work, we present a simple, mask-free, low-cost imprinted sensor based on laser scribed graphene (LSG) technology combined to molecularly imprinted polymers (MIPs) for BPA determination. CO 2 laser was used in production of LSG electrodes with high conductivity and multilayer structure by using less laser speed/ power (2.8 cm/s /3.2 W) and low resistivity 58 Ω/square on flexible polyimide sheet leading to the high active surface area of the sensor. LSG device was functionalized with imprinted polypyrrole with a known amount of BPA as template molecule to develop the sensor. The bare LSG, LSG-MIP, LSG-NIP sensors were characterized using Raman spectroscopy, SEM, XRD, AFM. The electrochemical measurements were carried out using cyclic voltammetry and differential pulse voltammetry. Experimental conditions were optimized, including the concentration of pyrrole monomer, the number of polymerization cycles, the concentration of BPA as template and the incubation time. We evaluated the sensitivity of the LSG-MIP sensor in the concentration range between 0.05 μM and 20 μM with a limit of detection of 8 nM. The proposed sensor exhibits high selectivity towards BPA compared to its structural analogs and good reusability. The developed sensor was successfully applied for the detection of BPA in tap, mineral water and in plastic samples. The developed sensor was integrated into a PMMA case connected to the potentiostat to achieve complete isolation and a practical measurement system. [ABSTRACT FROM AUTHOR]

A relative humidity (RH) sensor based on femtosecond laser induced spiral micro-structured single mode-multimode-single mode (FISM-SMS) fiber structure was experimentally demonstrated. The spiral micro-groove ablated multimode fiber of the FISM-SMS fiber structure was coated with RH sensitive polyvinyl alcohol (PVA) whose refractive index varies as a function of ambient humidity level. Due to the FISM-SMS fiber structure highly sensitive to ambient refractive index, transmission spectrum of the RH sensor changed greatly at different ambient relative humidity. RH response of the sensor was tested by putting it into a homemade climatic chamber whose humidity level can be adjusted by a series of saturated salt solutions. Experimental results show that a RH sensitivity of ∼650 pm/%RH with linearity of ∼0.99 when humidity level varies from 35 % RH to 70 % RH. Besides, reversibility and stability make the sensor a good candidate for RH sensing. [ABSTRACT FROM AUTHOR]