Off-plane quartz-enhanced photoacoustic spectroscopy.

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 ∼2 orders of magnitude. Furthermore, the radial and longitudinal resonance modes can be combined to further improve the sensor performance.

Two-dimensional beam scanning by tunable photonic spin Hall effect.

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.

Determinants and their spatial heterogeneity of carbon emissions in resource-based cities, China.

Global climate change associated with increased carbon emissions has become a global concern. Resource-based cities, by estimations, have emerged as major contributors to carbon emissions, accounting for approximately one-third of the national total. This underscores their pivotal role in the pursuit of carbon neutrality goals. Despite this, resource-based cities have long been neglected in current climate change mitigation policy discussions. Accordingly, using exploratory spatial data analysis and Geographical Weighted Regression method, this study investigates the determinants of carbon emissions and their spatial pattern in 113 resource-based cities in China. It can be concluded that: (1) The proportion of carbon emissions from resource-based cities in the national total has shown a marginal increase between 2003 and 2017, and the emissions from these cities have not yet reached their peak. (2) A relatively stable spatial pattern of "northeast high, southwest low" characterizes carbon emissions in resource-based cities, displaying significant spatial autocorrelation. (3) Population size, economic development level, carbon abatement technology, and the proportion of resource-based industries all contribute to the increase in carbon emissions in these cities, with carbon abatement technology playing a predominant role. (4) There is a spatial variation in the strength of the effects of the various influences.

Ppbv-level mid-infrared photoacoustic sensor for mouth alcohol test after consuming lychee fruits.

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 ∼9.3 µm with a power of 10 W. A detection limit of ∼18 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 ∼0.999. 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.

High-sensitivity humidity sensing of a U-shaped microfiber coated with porous methacryloxyethyl trimethyl ammonium chloride film.

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.

Correlation between TyG index and coronary atherosclerosis assessed by CCTA in elderly male patients: a cross-sectional study.

BACKGROUND: Age is a major risk factor associated with the complexity of coronary artery disease (CAD), and the prognosis of elderly patients with coronary heart disease is relatively poor. Metabolic disturbances are prevalent in the elderly population and contribute to CAD morbidity and mortality. This study aimed to investigate the relationship between the triglyceride-glucose (TyG) index and total coronary atherosclerotic burden assessed non-invasively by Coronary Computed Tomography Angiogram (CCTA) in the elderly population. METHODS: This retrospective cross-sectional study involved 427 patients who underwent CCTA. The patients were divided into two groups based on their Leiden score: ≥5 and < 5. Comparisons between groups were conducted using t-tests or Mann-Whitney U tests for continuous variables and chi-square tests for categorical variables. The correlation between TyG and Leiden score was assessed using Spearman's rank correlation coefficient. Univariable and multivariable logistic regression analyses were performed to assess the role of TyG in atherosclerosis risk, using clinical variables previously shown to independently predict a high Leiden score. RESULTS: The levels of age and HbA1c% were significantly higher in patients with Leiden score ≥ 5. Patients with Leiden score ≥ 5 showed no significant difference in TyG index compared to those with Leiden score < 5. Pearson correlation analysis showed that HbA1c% (r = 0.44, p < 0.01), age (r = 0.34, p < 0.01), and FBG (r = 0.15, p = 0.01) were positively correlated with Leiden score, while TyG index had no correlation with Leiden score (r = 0.05, p = 0.42). Multiple linear regression analysis showed that HbA1c% (ß = 2.92, 95%CI: 2.25-3.56, P < 0.01) was positively correlated with Leiden score, while TyG index had no correlation with Leiden score (ß = 0.73, 95%CI: -3.27-4.72, P < 0.01). HbA1c% was found to be an influential factor for obstructive CVD (ß = 1.86, 95%CI: 1.50-2.29, P < 0.01), while TyG index was not an independent risk factor for obstructive CVD (ß = 0.39, 95%CI: 0.12-1.32, P = 0.13). CONCLUSION: The TyG index did not show any significant correlation with the Leiden score and obstructive CVD as a risk factor in elderly male population. On the other hand, HbA1c% was identified as an influential factor for both the Leiden score and obstructive CVD.

Helmholtz-resonator quartz-enhanced photoacoustic spectroscopy.

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 1.39 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.

Quartz-Enhanced Photoacoustic Spectroscopy-Conductance Spectroscopy for Gas Mixture Analysis.

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.

Side-excitation light-induced thermoelastic spectroscopy.

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.

Black Arsenic-Phosphorus Nanosheets for Highly Responsive Photodetection and Dual-Wavelength Ultrafast Pulse Generation at Telecommunication Bands.

Black arsenic-phosphorus (b-AsP), an alloy containing black phosphorus and arsenic in the form of b-AsxP1-x, has a broadly tunable band gap changing with the chemical ratios of As and P. Although mid-infrared photodetectors and mode-locked or Q-switched pulse lasers based on b-AsP (mostly b-As0.83P0.17) are investigated, the potential of this family of materials for near-infrared photonic and optoelectronic applications at telecommunication bands is not fully explored. Here, we have verified a multifunctional fiber device based on b-As0.4P0.6 nanosheets for highly responsive photodetection and dual-wavelength ultrafast pulse generation at around 1550 nm. The fiber laser with a saturable absorber (SA) based on b-As0.4P0.6 nanosheets can output dual-wavelength mode-locking pulses with a larger bandwidth and spectral separation than those based on other two-dimensional (2D) materials. Remarkably, it is found that the b-As0.4P0.6-based photodetector can achieve a high responsivity of 10,200 A/W at 1550 nm and a peak responsivity of 2.29 × 105 A/W at 980 nm. Our work suggests that b-As0.4P0.6 shows great potential in ultrafast photonics, dual-comb spectroscopy, and infrared signal detection.

Joint spatial weak measurement with higher-order Laguerre-Gaussian point states.

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 〈X〉 and 〈Y〉 as well as high-order position operators 〈XY〉, 〈X2 - Y2〉, 〈X3〉, and 〈Y3〉 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.

Clamp-type quartz tuning fork enhanced photoacoustic spectroscopy.

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 ∼30 times has been obtained with a single-tube acoustic micro resonator length of 8 mm, ∼20% shorter than the dual-tube micro-resonator employed in a conventional QEPAS system.

Spider Silk-Improved Quartz-Enhanced Conductance Spectroscopy for Medical Mask Humidity Sensing.

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.

Integrated near-infrared QEPAS sensor based on a 28 kHz quartz tuning fork for online monitoring of CO2 in the greenhouse.

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 28 kHz was employed as an acoustic wave transducer. A near-infrared DFB laser diode emitting at 2004 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 32 kHz QTF, the QEPAS signal amplitude increased by > 2 times by the integrated QEPAS module based on a 28 kHz QTF. At atmospheric pressure, a 5.4 ppm detection limit at a CO2 absorption line of 4991.25 cm-1 was achieved with an integration time of 1 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 0.7 ppm when the integration time was 125 s. A portable CO2 sensor system based on QEPAS was developed for 24 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.

High-power near-infrared QEPAS sensor for ppb-level acetylene detection using a 28 kHz quartz tuning fork and 10 W EDFA.

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 ∼7 ppb was achieved for C2H2 detection, corresponding to a normalized noise equivalent absorption coefficient of 4.4×10-8cm-1 · W · Hz-1/2.

Ppb-level gas detection using on-beam quartz-enhanced photoacoustic spectroscopy based on a 28 kHz tuning fork.

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.

Ultrasensitive temperature sensor and mode converter based on a modal interferometer in a two-mode fiber.

This paper presents an ultrasensitive temperature sensor and tunable mode converter based on an isopropanol-sealed modal interferometer in a two-mode fiber. The modal interferometer consists of a tapered two-mode fiber (TTMF) sandwiched between two single-mode fibers. The sensor provides high-sensitivity temperature sensing by taking advantages of TTMF, isopropanol and the Vernier-like effect. The TTMF provides a uniform modal interferometer with LP01 and LP11 modes as well as strong evanescent field on its surface. The temperature sensitivity of the sensor can be improved due to the high thermo-optic coefficient of isopropanol. The Vernier-like effect based on the overlap of two interference spectra is applied to magnify the sensing capabilities with a sensitivity magnification factor of 58.5. The temperature sensor is implemented by inserting the modal interferometer into an isopropanol-sealed capillary. The experimental and calculated results show the transmission spectrum exhibit blue shift with increasing ambient temperature. Experimental results show that the isopropanol-sealed modal interferometer provides a temperature sensitivity up to -140.5 nm/°C. The interference spectrum has multiple dips at which the input LP01 mode is converted to the LP11 mode. This modal interferometer acts as a tunable multi-channel mode converter. The mode converter that can be tuned by varying temperature and mode switch is realized.

High-performance photonic spin Hall effect in anisotropic epsilon-near-zero metamaterials.

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.

Radial-cavity quartz-enhanced photoacoustic spectroscopy.

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.