- 标题
- 摘要
- 关键词
- 实验方案
- 产品
-
[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) - Broadband Multi-Species Trace Gas Detection by Up-Converting Mid-Infrared Supercontinuum Light into the Near-Infrared
摘要： Recent advancement in compact, stable, and broadband mid-infrared supercontinuum (SC) sources has provided attractive scientific and industrial applications in metrology, sensing, and communications [1]. The wide spectral coverage in the so-called molecular fingerprint region is the main advantage of such SC sources, opening up new opportunities for efficient multi-species trace gas detection at short time scale. Presently, there is a lack of sensitive, low-cost, uncooled MIR photodetectors. The alternative approach involves up-converting mid-infrared light into the near-infrared region via non-linear conversion, leveraging the benefits of sensitive and cost-effective CCD detectors [2]. Here, we present the development of a multi-species trace gas sensor utilizing a mid-infrared SC source in combination with a multipass absorption cell and an up-conversion-based spectrometer. The customized SC source (NKT Photonics) has a total power of 450 mW covering the 1.5 – 4.5 μm spectral window. The astigmatic Herriott multipass cell (AMAC-76, Aerodyne Research) provides an effective optical pathlength of 76 meters improving the detection sensitivity. Details of the up-conversion-based spectrometer (NLIR) have been recently published. [3]. Note that in the present upconversion system the intracavity laser at 1064 nm is generated by pumping the Nd:YVO4 gain medium at 808 nm instead of 880 nm. In order to enhance the long term stability for single species detection, the amplitude drift of the SC source is minimized by counterbalancing the SC intensity with a non-absorbing reference. Multispecies broadband absorbance spectra have been obtained for, amongst others, mixtures of ethane and acetaldehyde at ppm levels in nitrogen as shown in Fig. 1 (a). A non-negative least squares global fitting method has been applied to extract the concentration of individual sub-component. To check system linearity by different gas concentrations, the absorbance with various mixing ratios were measured at a pressure of 900 mar for 60 s. A linear fit of these measurements that agreed with the calculated ones is depicted in Fig. 1 (b) for ethane. The sensor is capable of detecting sub-ppmv gas concentrations (e.g. ~300 ppbv ethane) in a wide range of spectrum (over 600 cm-1) with a ~5 cm-1 spectral resolution. Broadening the spectrum to a wider range by using chirped crystals in the up-converter system and further experiments are under progress. More details and the results for the on-going experiments will be presented at the conference.
关键词： multi-species,mid-infrared supercontinuum,up-conversion,broadband,trace gas detection
更新于2025-09-16 10:30:52
-
Application of Near-Infrared Optical Feedback Cavity Enhanced Absorption Spectroscopy (OF-CEAS) to the Detection of Ammonia in Exhaled Human Breath
摘要： The qualitative and quantitative analysis to trace gas in exhaled human breath has become a promising technique in biomedical applications such as disease diagnosis and health status monitoring. This paper describes an application of a high spectral resolution optical feedback cavity enhanced absorption spectroscopy (OF-CEAS) for ammonia detection in exhaled human breath, and the main interference of gases such as CO2 and H2O are approximately eliminated at the same time. With appropriate optical feedback, a fibered distributed feedback (DFB) diode laser emitting at 1531.6 nm is locked to the resonance of a V-shaped cavity with a free spectral range (FSR) of 300 MHz and a finesse of 14,610. A minimum detectable absorption coefficient of αmin = 2.3 × 10?9 cm?1 is achieved in a single scan within 5 s, yielding a detection limit of 17 ppb for NH3 in breath gas at low pressure, and this stable system allows the detection limit down to 4.5 ppb when the spectra to be averaged over 16 laser scans. Different from typical CEAS with a static cavity, which is limited by the FSR in frequency space, the attainable spectral resolution of our experimental setup can be up to 0.002 cm?1 owing to the simultaneous laser frequency tuning and cavity dither. Hence, the absorption line profile is more accurate, which is most suitable for low-pressure trace gas detection. This work has great potential for accurate selectivity and high sensitivity applications in human breath analysis and atmosphere sciences.
关键词： trace gas detection,breath gas analysis,ammonia,optical feedback,cavity enhanced absorption spectroscopy
更新于2025-09-11 14:15:04
-
[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) - A 12.6 – 15 μm Mid-IR Source Based on Difference Frequency Generation in Orientation-Patterned GaAs
摘要： Tunable laser sources in the mid-infrared (mid-IR) spectral range have been of great interest for a variety of applications such as molecular spectroscopy and trace gas detection. Difference-frequency generation (DFG) based on nonlinear frequency conversion in nonlinear crystals has been an effective approach to realize tunable mid-IR laser sources [1]. Among nonlinear crystals, orientation-patterned (OP) GaAs has been highly attractive for mid-IR DFG laser sources due to its large nonlinear susceptibility, lack of birefringence, wide transparency range (0.9 – 17 μm), high thermal conductivity, and high laser-damage-threshold [2,3]. Here, we report the generation of broadly tunable mid-IR radiation across 12.65 – 15 μm based on the DFG approach using an OP-GaAs crystal.
关键词： mid-IR,difference-frequency generation,orientation-patterned GaAs,tunable laser sources,molecular spectroscopy,trace gas detection
更新于2025-09-11 14:15:04
-
[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) - Dual-Colour-Pump Broadband CARS in Single-Ring Gas-Filled Photonic Crystal Fibre
摘要： Selective detection and chemical analysis of trace gases at concentration levels of parts per million (ppm) and below is of critical importance in environmental monitoring and medicine. Spectroscopic techniques offer high gas-type selectivity and are widely used for measuring the concentration of specific molecular species. Raman spectroscopy provides two key advantages. First, the pump wavelength can be freely chosen, independently of the absorption lines of the gas. Second, the highest Raman frequency shift of any gas is the vibrational transition of H2 at 125 THz, which means that all known Raman active molecules can be detected with one spectrometer. We report coherent anti-Stokes Raman spectroscopy (CARS) in single-ring hollow-core photonic crystal fibre (SR-PCF) using a dual-colour pump. The long collinear path-length offered by SR-PCF strongly enhances the efficiency of the Raman interactions, and furthermore the gas-filled SR-PCF has a zero dispersion wavelength which is pressure tuneable. By selecting an appropriate pressure, the dispersion can be arranged to be anomalous in the visible and at the same time normal in the ultraviolet. Under these circumstances, by fine-tuning the pressure to minimize dephasing, the Raman coherence prepared by seeded pumping in the visible can be used for phase-matched generation of an anti-Stokes signal from a second pump in the ultraviolet. This spectrally separates the 'preparation' pump from the 'read-out' pump. The low dephasing rate in the ultraviolet permits efficient generation, along the whole fibre length, of anti-Stokes signals from all known Raman-active gas molecules, which is a significant advantage compared to other spectroscopic techniques. The dual-colour pump scheme allows the main detection limit of CARS imposed by the non-resonant background (NRB) to be overcome. It exploits the fact that the NRB is a quasi-instantaneous effect, present only when pump and seed pulses overlap. Although this is also a requirement of Raman excitation, the resulting coherence wave has a lifetime of nanoseconds before it relaxes through intermolecular collisions. Therefore, by appropriately delaying the read-out pump pulse, it is possible to suppress the NRB. Figure 1(a) shows the CARS spectrum for two trace gases, H2 (500 ppm) and CH4 (600 ppm), mixed with the buffer gas N2, measured when the read-out pump overlaps with the Stokes seed. Figure 1 (b) shows the CARS spectrum for 20 ppm of H2 and 350 ppm of CH4, measured when the pump was delayed by 2 ns with respect to the Stokes seed. As can be seen from Fig.1, the dual-colour-pump CARS scheme in SR-PCF reduces the NRB by 120 dB, improving the detection limit by 15 dB and allowing detection of trace gas concentrations as low as 20 ppm with only 20 kW of peak pump power. This novel dual-colour-pump CARS approach has great potential in environmental monitoring and medical applications, offering high sensitivity, short acquisition times (several seconds) and simultaneous multi-species sensing.
关键词： Raman spectroscopy,photonic crystal fibre,dual-colour pump,CARS,trace gas detection
更新于2025-09-11 14:15:04
-
Parts-per-billion-level detection of hydrogen sulfide based on near-infrared all-optical photoacoustic spectroscopy
摘要： A highly sensitive trace hydrogen sulfide (H2S) gas sensing scheme based on all-optical photoacoustic spectroscopy is demonstrated. A high-power erbium-doped fiber amplified near-infrared laser is used as a light source for acoustic excitation. Meanwhile, the second-harmonic photoacoustic signal is measured by a fiber-optic cantilever microphone which is equipped with a white-light interferometric readout. For sensitivity improvement, the demodulated digital photoacoustic signal is processed by a virtual lock-in amplifier. The continuous H2S measurement experiment shows the ability of real-time response. A detection limit is achieved to be 33 ppb with a 10 s measurement time at the wavelength of 1576.29 nm. With both the excitation light and the probe light being transmitted by optical fibers, the designed sensing system has the advantages of remote detection and immunity to electromagnetic interference.
关键词： Trace gas detection,Photoacoustic spectroscopy,Fiber-optic sensing,Cantilever microphone,Near-infrared laser
更新于2025-09-10 09:29:36