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Hydrogen cyanide (HCN) is a toxic industrial chemical, necessitating low-level detection capabilities for safety and environmental monitoring. This study introduces a novel approach for detecting hydrogen cyanide (HCN) using a clamp-type custom quartz tuning fork (QTF) integrated with a dual-tube acoustic micro-resonator (AmR) for enhanced photoacoustic gas sensing. The design and optimization of the AmR geometry were guided by theoretical simulation and experimental validation, resulting in a robust on-beam QEPAS (Quartz-Enhanced Photoacoustic Spectroscopy) configuration. To boost the QEPAS sensitivity, an Erbium-Doped Fiber Amplifier (EDFA) was incorporated, amplifying the laser power by approximately 286 times. Additionally, a transformer-based U-shaped neural network, a machine learning filter, was employed to refine the photoacoustic signal and reduce background noise effectively. This combination yielded a significantly low detection limit for HCN at 0.89 parts per billion (ppb) with a rapid response time of 1â¯second, marking a substantial advancement in optical gas sensing technologies. Key modifications to the QTF and innovative use of AmR lengths were validated under various experimental conditions, affirming the system's capabilities for real-time, high-sensitivity environmental monitoring and industrial safety applications. This work not only demonstrates significant enhancements in QEPAS but also highlights the potential for further technological advancements in portable gas detection systems.
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Lateral momentum conservation is typically kept in a non-absorptive rotationally symmetric system through mirror symmetry via Noether's theorem when illuminated by a homogeneous light wave. Therefore, it is still very challenging to break the mirror symmetry and generate a lateral optical force (LOF) in the rotationally symmetric system. Here, we report a general dynamic action in the SO(2) rotationally symmetric system, originating from the polarization-tuned mirror symmetry breaking (MSB) of the light scattering. We demonstrate theoretically and experimentally that MSB can be generally applied to the SO(2) rotationally symmetric system and tuned sinusoidally by polarization orientation, leading to a highly tunable and highly efficient LOF (9.22 pN/mW/µm-2) perpendicular to the propagation direction. The proposed MSB mechanism and LOF not only complete the sets of MSB of light-matter interaction and non-conservative force only using a plane wave but also provide extra polarization manipulation freedom.
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To the best of our knowledge, a novel tunable photonic spin Hall effect is proposed based on a pair of liquid crystal Pancharatnam-Berry (PB) lenses. Owing to the spin-dependent geometric phases, a PB lens focus or defocus the incident light field according to its spin angular momentum. By cascading two PB lenses with a small gap, the focus and defocus effects can be suppressed, and the transmitted light fields with opposite spin will be deflected toward opposite directions when the two PB lenses have a relative lateral displacement. The deflection angles vary linearly with the displacements, thus double-lines two-dimensional continuous beam scanning is achieved with a scanning angle of 39o × 39° and a beam diverging angle of 0.028o × 0.028°. The scanning beam is used to write different patterns on a 200 nm thick gold film. We believe this beam scanning system can find wide applications ranging from laser processing, Lidar, particle manipulation, to free space optical communications.
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In this work, we developed off-plane quartz-enhanced photoacoustic spectroscopy (OP-QEPAS). In the OP-QEPAS the light beam went neither through the prong spacing of the quartz tuning fork (QTF) nor in the QTF plane. The light beam is in parallel with the QTF with an optimal distance, resulting in low background noise. A radial-cavity (RC) resonator was coupled with the QTF to enhance the photoacoustic signal by the radial resonance mode. By offsetting both the QTF and the laser position from the central axis, we enhance the effect of the acoustic radial resonance and prevent the noise generated by direct laser irradiation of the QTF. Compared to IP-QEPAS based on a bare QTF, the developed OP-QEPAS with a RC resonator showed a >10× signal-to-noise ratio (SNR) enhancement. The OP-QEPAS system has great advantages in the use of light emitting devices (LEDs), long-wavelength laser sources such as mid-infrared quantum cascade lasers, and terahertz sources. When employing a LED as the excitation source, the noise level was suppressed by â¼2 orders of magnitude. Furthermore, the radial and longitudinal resonance modes can be combined to further improve the sensor performance.
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A ppbv-level mid-infrared photoacoustic spectroscopy sensor was developed for mouth alcohol tests. A compact CO2 laser with a sealed waveguide and integrated radio frequency (RF) power supply was used. The emission wavelength is â¼9.3 µm with a power of 10 W. A detection limit of â¼18 ppbv (1σ) for ethanol gas with an integration of 1 s was achieved. The sensor performed a linear dynamic range with an R square value of â¼0.999. A breath measurement experiment after consuming lychees was conducted. The photoacoustic signal amplitude decreased with the quality of lychee consumed, confirming the existence of residual alcohol in the mouth. During continuous measurement, the photoacoustic signal decreased in < 10 min when consuming 30 g lychee fruits, proving that the alcohol detected in exhaled breath originated from the oral cavity rather than the bloodstream. This work provided valuable information on the distinction of alcoholism and crime.
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We demonstrate an intensity-modulated humidity sensor based on a U-shaped microfiber coated with porous methacryloxyethyl trimethyl ammonium chloride (DMC) film. The high surface-to-volume ratios of the porous structure improve the interaction between the DMC film and water molecules, resulting in significantly enhanced sensitivity of the humidity sensor. In the humidity range of 34.0%RH to 50.0%RH, the humidity sensitivity of this microfiber sensor is up to 3.090 dB/%RH, which is six times higher than that of other fiber humidity sensors. The humidity detection range can be adjusted with high humidity sensitivity (≥1.685d B/% R H) by controlling the microfiber diameter and bent diameter. Furthermore, this type of sensor has a fast recovery time of 0.023 s and a response time of only 0.692 s. This type of sensor has broad potential applications in chemical processing, medical diagnostics, instrument manufacturing, and so on.
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A novel spectroscopic method, named quartz-enhanced photoacoustic spectroscopy-conductance spectroscopy (QEPAS-CS), was first developed for gas mixture analysis. In QEPAS-CS, the advantage of photoacoustic detection and conductance analysis was realized by a quartz tuning fork (QTF). Two-component gas analysis was done by photoacoustic detection and conductance detection. For an explicit application, natural spider silk was used as a water vapor transducer to modify the QTF, making a conductance sensing channel. A 2004 nm laser diode was used as an excitation source for a photoacoustic sensing channel. Such a QEPAS-CS sensor was used for H2O/CO2 gas mixture analysis in a cell incubator. This provides a solution to calibrate an infrared photoacoustic spectroscopy gas sensor. This example effectively confirms the capacity of multigas analysis by the QEPAS-CS sensor.
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In this work, Helmholtz-resonator quartz-enhanced photoacoustic spectroscopy (HR-QEPAS) was developed for trace gas sensing. A pair of Helmholtz resonators with high-order resonance frequency was designed and coupled with a quartz tuning fork (QTF). Detailed theoretical analysis and experimental research were carried out to optimize the HR-QEPAS performance. As a proof-of-concept experiment, the water vapor in the ambient air was detected using a 1.39â µm near-infrared laser diode. Benefiting from the acoustic filtering of the Helmholtz resonance, the noise level of QEPAS was reduced by >30%, making the QEPAS sensor immune to environmental noise. In addition, the photoacoustic signal amplitude was improved significantly by >1 order of magnitude. As a result, the detection signal-to-noise ratio was enhanced by >20 times, compared with a bare QTF.
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In this Letter, a side-excitation light-induced thermoelastic spectroscopy (SE-LITES) technique was developed for trace gas detection. A novel, to the best of our knowledge, custom quartz tuning fork (QTF) was used as a transducer for photon detection by the thermoelastic effect. The mechanical stress distribution on the QTF surface was analyzed to identify the optimum thermoelastic excitation approach. The electrode film on the QTF surface also works as a partially reflective layer to obtain a long optical absorption path inside the QTF body. With the long optical absorption length and the inner face excitation of the QTF, the thermoelastic effect was greatly enhanced. With an optimized modulation depth, a signal-to-noise ratio (SNR) improvement of more than one order of magnitude was achieved, compared to traditional LITES.
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In this Letter, a sensitive light-induced thermoelastic spectroscopy (LITES)-based trace gas sensor by exploiting a super tiny quartz tuning fork (QTF) was demonstrated. The prong length and width of this QTF are 3500â µm and 90â µm, respectively, which determines a resonant frequency of 6.5 kHz. The low resonant frequency is beneficial to increase the energy accumulation time in a LITES sensor. The geometric dimension of QTF on the micrometer scale is advantageous to obtain a great thermal expansion and thus can produce a strong piezoelectric signal. The temperature gradient distribution of the super tiny QTF was simulated based on the finite element analysis and is higher than that of the commercial QTF with 32.768 kHz. Acetylene (C2H2) was used as the analyte. Under the same conditions, the use of the super tiny QTF achieved a 1.64-times signal improvement compared with the commercial QTF. The system shows excellent long-term stability according to the Allan deviation analysis, and a minimum detection limit (MDL) would reach 190 ppb with an integration time of 220 s.
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Here, joint spatial weak measurements with higher-order Laguerre-Gaussian (LG) point states are investigated experimentally. From the intensity patterns of the final LG point states, two dimensional position operators ãXã and ãYã as well as high-order position operators ãXYã, ãX2 - Y2ã, ãX3ã, and ãY3ã are extracted simultaneously, from which both the complex weak values and joint weak values of two non-commuting observables can be obtained. The enhancement of joint weak values by the postselection state are analyzed. The simple relationship between the expectation values of position operators and the azimuthal and radial indexes of LG modes allows us to identify the mode indexes directly. A simple and robust scheme based on an optical window is demonstrated to monitor the LG mode indexes. These findings deepen the understanding of the weak measurement and provide an alternate and effective method for LG mode index monitoring.
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In this Letter, clamp-type quartz tuning fork enhanced photoacoustic spectroscopy (Clamp-type QEPAS) is proposed and realized through the design, realization, and testing of clamp-type quartz tuning forks (QTFs) for photoacoustic gas sensing. The clamp-type QTF provides a wavefront-shaped aperture with a diameter up to 1 mm, while keeping Q factors > 104. This novel, to the best of our knowledge, design results in a more than ten times increase in the area available for laser beam focusing for the QEPAS technique with respect to a standard QTF. The wavefront-shaped clamp-type prongs effectively improve the acoustic wave coupling efficiency. The possibility to implement a micro-resonator system for clamp-type QTF is also investigated. A signal-to-noise enhancement of â¼30 times has been obtained with a single-tube acoustic micro resonator length of 8 mm, â¼20% shorter than the dual-tube micro-resonator employed in a conventional QEPAS system.
Asunto(s)
Cuarzo , Cuarzo/química , Análisis Espectral/métodosRESUMEN
Spider silk is one of the hottest biomaterials researched currently, due to its excellent mechanical properties. This work reports a novel humidity sensing platform based on a spider silk-modified quartz tuning fork (SSM-QTF). Since spider silk is a kind of natural moisture-sensitive material, it does not demand additional sensitization. Quartz-enhanced conductance spectroscopy (QECS) was combined with the SSM-QTF to access humidity sensing sensitively. The results indicate that the resonance frequency of the SSM-QTF decreased monotonously with the ambient humidity. The detection sensitivity of the proposed SSM-QTF sensor was 12.7 ppm at 1 min. The SSM-QTF sensor showed good linearity of ~0.99. Using this sensor, we successfully measured the humidity of disposable medical masks for different periods of wearing time. The results showed that even a 20 min wearing time can lead to a >70% humidity in the mask enclosed space. It is suggested that a disposable medical mask should be changed <2 h.
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Cuarzo , Seda , Humedad , Cuarzo/química , Análisis Espectral/métodosRESUMEN
In this paper, a highly sensitive and integrated near-infrared CO2 sensor was developed based on quartz-enhanced photoacoustic spectroscopy (QEPAS). Unlike traditional QEPAS, a novel pilot line manufactured quartz tuning fork (QTF) with a resonance frequency f 0 of 28â¯kHz was employed as an acoustic wave transducer. A near-infrared DFB laser diode emitting at 2004â¯nm was employed as the excitation light source for CO2 detection. An integrated near-infrared QEPAS module was designed and manufactured. The QTF, acoustic micro resonator (AmR), gas cell, and laser fiber are integrated, resulting in a super compact acoustic detection module (ADM). Compared to a traditional 32â¯kHz QTF, the QEPAS signal amplitude increased by >â¯2 times by the integrated QEPAS module based on a 28â¯kHz QTF. At atmospheric pressure, a 5.4â¯ppm detection limit at a CO2 absorption line of 4991.25â¯cm-1 was achieved with an integration time of 1â¯s. The long-term performance and stability of the CO2 sensor system were investigated using Allan variance analysis. Finally, the minimum detection limit (MDL) was improved to 0.7â¯ppm when the integration time was 125â¯s. A portable CO2 sensor system based on QEPAS was developed for 24â¯h continuous monitoring of CO2 in the greenhouse located in Guangzhou city. The CO2 concentration variations were clearly observed during day and night. Photosynthesis and respiration plants can be further researched by the portable CO2 sensor system.
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A high-power near-infrared (NIR) quartz enhanced photoacoustic spectroscopy (QEPAS) sensor for part per billion (ppb) level acetylene (C2H2) detection was reported. A 1536 nm distributed feedback (DFB) diode laser was used as the excitation light source. Cooperated with the laser, a C-band 10 W erbium-doped fiber amplifier (EDFA) was employed to boost the optical excitation power to improve QEPAS detection sensitivity. A pilot line manufactured quartz tuning fork (QTF) with a resonance frequency of 28 kHz was used as the photoacoustic transducer. In the case of high excitation power, gas flow effect and temperature effect were found and studied. Benefitting from the low QTF resonance frequency, high excitation power, and vibrational-translational (V-T) relaxation promoter, a detection limit of â¼7 ppb was achieved for C2H2 detection, corresponding to a normalized noise equivalent absorption coefficient of 4.4×10-8cm-1 · W · Hz-1/2.
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In this paper, an on-beam quartz-enhanced photoacoustic spectroscopy (QEPAS) sensor based on a custom quartz tuning fork (QTF) acting as a photoacoustic transducer, was realized and tested. The QTF is characterized by a resonance frequency of 28 kHz, ~15% lower than that of a commercially available 32.7 kHz standard QTF. One-dimensional acoustic micro resonator (AmR) was designed and optimized by using stainless-steel capillaries. The 28 kHz QTF and AmRs are assembled in on-beam QEPAS configuration. The AmR geometrical parameters have been optimized in terms of length and internal diameter. The laser beam focus position and the AmR coupling distance were also adjusted to maximize the coupling efficiency. For comparison, QEPAS on-beam configurations based on a standard QTF and on the 28 kHz QTF were compared in terms of H2O and CO2 detection sensitivity. In order to better characterize the performance of the system, H2O, C2H2 and CO2 were detected for a long time and the long-term stability was analyzed by an Allan variance analysis. With the integration time of 1 s, the detection limits for H2O, C2H2 and CO2 are 1.2 ppm, 28.8 ppb and 2.4 ppm, respectively. The detection limits for H2O, C2H2 and CO2 can be further improved to 325 ppb, 10.3 ppb and 318 ppb by increasing the integration time to 521 s, 183 s and 116 s.
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A high-performance photonic spin Hall effect is demonstrated in an anisotropic epsilon-near-zero (ENZ) metamaterial based on the wave-vector-varying Pancharatnam-Berry phase. The giant out-of-plane anisotropy of ENZ metamaterial induces strong spin-orbit coupling. With a small incident angle, photons with opposite spins move along opposite transverse directions gradually. After transmitting through a submicrometer thick ENZ metamaterial, the spin photons are fully separated with a spin separation of 2.7 times beam waist and transmittance of 70.1%, allowing a figure of merit F up to 1.9. A practical ENZ metamaterial consisting of an Ag nanorod array is proposed, whose figure of merit is still up to 0.006. This high-performance photonic spin Hall effect provides an integrated and practical way for the development of spin-photonic devices.
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Radial-cavity quartz-enhanced photoacoustic spectroscopy (RC-QEPAS) was proposed for trace gas analysis. A radial cavity with (0,0,1) resonance mode was coupled with the quartz tuning fork (QTF) to greatly enhance the QEPAS signal and facilitate the optical alignment. The coupled resonance enhancement effects of the radial cavity and QTF were analyzed theoretically and researched experimentally. With an optimized radial cavity, the detection sensitivity of QEPAS was enhanced by >1 order of magnitude. The RC-QEPAS makes the acoustic detection module more compact and optical alignment comparable with a bare QFT, benefiting the usage of light sources with poor beam quality.
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Monolayer transition metal dichalcogenides have intrinsic spin-valley degrees of freedom, drawing broad interests due to their potential applications in information storage and processing. Here, we demonstrate the possibility of using cylindrical vector pumped beams, which are nonseparable in their polarization and spatial modes, to manipulate nonlinear valley-locked twisted-vortex emissions in monolayer tungsten disulfide (WS2). The second-harmonic (SH) photons from K and K' valleys are encoded with opposite optical vortices, thus allowing the SH beams to emerge as cylindrical vector beams with doubled topological orders compared to the fundamental beams. The conically refracted pumped beams allow us to generate the first-order SH cylindrical vector and full Poincaré beams via tuning the valley-locked emitted light field profiles. With fanshaped WS2 films breaking the axial symmetry of SH beams, the SH valley photons are routed to opposite directions. Our results pave the way to develop atomically thin nonlinear photonic devices and valleytronic nanodevices.
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An all-fiber integrated photodetector is proposed and demonstrated by assembling a graphene/palladium diselenide (PdSe2) Van der Waals heterostructure onto the endface of a standard optical fiber. A gold film is covered on the heterostructure working as an electrode and a mirror, which reflects back the unabsorbed residual light for further reusage. Owing to the low bandgap of PdSe2, the all-fiber photodetector shows a broadband photoresponse from 650 to 1550â nm with a high photoresponsivity of 6.68×104 AW-1, enabling a low light detection of 42.5 pW. And the fastest temporal response is about 660 µs. Taking advantage of heterostructures, the photodetector can work in self-powered mode with the on/off ratio about 82. These findings provide new strategies for integrating two-dimensional materials into optical fibers to realize integrated all-fiber devices with multi-function applications.