All-Fiber Tunable Pulsed 1.7 μm Fiber Lasers Based on Stimulated Raman Scattering of Hydrogen Molecules in Hollow-Core Fibers

Fiber lasers that operate at 1.7 μm have important applications in many fields, such as biological imaging, medical treatment, etc. Fiber gas Raman lasers (FGRLs) based on gas stimulated Raman scattering (SRS) in hollow-core photonic crystal fibers (HC-PCFs) provide an elegant way to realize efficient 1.7 μm fiber laser output. Here, we report the first all-fiber structure tunable pulsed 1.7 μm FGRLs by fusion splicing a hydrogen-filled HC-PCF with solid-core fibers. Pumping with a homemade tunable pulsed 1.5 μm fiber amplifier, efficient 1693~1705 nm Stokes waves are obtained by hydrogen molecules via SRS. The maximum average output Stokes power is 1.63 W with an inside optical–optical conversion efficiency of 58%. This work improves the compactness and stability of 1.7 μm FGRLs, which is of great significance to their applications.     

Characteristics of several NIR tuneable diode lasers for spectroscopic based gas sensing: a comparison

Tuneable laser diodes were characterized and compared for use as tuneable sources in gas absorption spectroscopy. Specifically, the characteristics of monolithic widely tuneable single frequency lasers, such as sampled grating distributed Bragg reflector laser and modulated grating Y-branch laser diodes, recently developed for optical communications, with operating wavelengths in the 1,520 nm相似文献   

1．5μm波段连续单频光纤激光器的研究进展

连续单频光纤激光器在光纤通信、光纤传感、引力波探测、激光雷达、非线性频率转换、光谱学等领域有着广泛的应用前景,发展十分迅速．近20年来,1．5μm波段连续单频光纤激光性能不断提高,如激光线宽从兆赫兹到千赫兹、功率从毫瓦到近百瓦量级,但激光器的噪声抑制、放大线宽展宽、输出功率等仍有待进一步研究．本文回顾了获得1．5μm波段连续单频激光输出的关键技术,总结了本课题组基于磷酸盐玻璃光纤短腔Bragg反射（DBR）结构实现1．5μm波段连续单频光纤激光性能,以及单频激光功率放大的研究进展．     

Preliminary results of heterodyne detection with quantum-cascade lasers in the 9 μm region

In this paper, we describe recent results in mid-infrared heterodyne detection using quantum-cascade (QC) lasers as local oscillator (LO). In the 9 μm range, the heterodyne detection technique was first developed with CO₂ lasers and then with Pb-salt diode lasers. Quantum-cascade lasers are promising high quality tunable mid-infrared sources. We developed a quantum-cascade laser based heterodyne spectrometer. Atmospheric absorption spectra of ozone are presented.     

便携式微型液相色谱仪的研制

该工作报道了一种自行设计研制的便携式微型液相色谱仪(portable micro liquid chromatograph, p-μLC)。p-μLC集成了二元大推力注射泵作为流动相驱动装置、毛细管整体柱为分离介质和紫外-可见/荧光两用流通池为在线检测单元。自行设计研制的二元大推力注射泵可以实现等度/梯度洗脱和流动相再装填功能,可控流速范围在0.025 μL/min到5.6 mL/min之间;自制的甲基丙烯酸酯C-18有机聚合物毛细管整体微柱可实现自有机小分子至生物大分子的分离;自行研制的光纤式紫外-可见/荧光两用流通池,可以通过光纤导入来自光源的紫外光和可见光,并采集透射光和与入射光反方向射出的荧光信号,流通池内使用自聚焦透镜和全反射光导毛细管等器件提高通光效率和吸收光程;两用流通池通过光纤分别连接由大功率发光二极管/脉冲氙灯光源和微型光栅光谱仪所组成的检测装置进行在线吸收和荧光光谱检测,检测波长范围为220~700 nm。p-μLC采用整体手提箱式结构,流路模块、检测模块等位于下主箱体中,采集、控制模块等位于上盖中,全重不超过8 kg。仪器由装载了自编控制采集软件的内置平板电脑进行控制和数据采集。使用自行制备的甲基丙烯酸酯C-18有机聚合物毛细管整体柱,在等度洗脱模式下,在p-μLC上分离了烷基苯化合物混合样品,其分离检测效果可以与商品化大型HPLC仪器相媲美。     

Preliminary results of heterodyne detection with quantum-cascade lasers in the 9 microm region

In this paper, we describe recent results in mid-infrared heterodyne detection using quantum-cascade (QC) lasers as local oscillator (LO). In the 9 microm range, the heterodyne detection technique was first developed with CO(2) lasers and then with Pb-salt diode lasers. Quantum-cascade lasers are promising high quality tunable mid-infrared sources. We developed a quantum-cascade laser based heterodyne spectrometer. Atmospheric absorption spectra of ozone are presented.     

New improvements in methane detection using a Helmholtz resonant photoacoustic laser sensor: a comparison between near-IR diode lasers and mid-IR quantum cascade lasers

Atmospheric methane was detected by combining a photoacoustic (PA) sensor with several lasers emitting in both the near- and mid-infrared spectral ranges to check the achievable detection limits. The PA spectrometer is based on differential Helmholtz resonance. Near-infrared telecommunication-type laser diodes of increasing power, from Sensors Unlimited Inc. and Anritsu, were first used to scan the 2 nu(3) band of CH(4) near 1.65 microm. The best achieved detection limit is 0.15 ppm of methane at atmospheric pressure and with a 1s integration time. The PA sensor was then operated in conjunction with a quantum cascade laser from Alpes Lasers emitting near 7.9 microm on the nu(4) band of CH(4). The achieved detection limit is then of 3 ppb. The dramatic improvement in the detection limit obtained with the QC laser is due to the stronger optical power as well as to the capability of reaching the fundamental bands of methane lying in the mid-infrared spectral range.     

共掺稀土离子对Er~(3+)激活中红外激光晶体光谱性能的影响

Er3+掺杂的晶体能够产生2.7~3.0μm波段中红外激光,在激光医疗、光通讯、环境探测和光电对抗等领域具有重要的应用。基于本课题组近年来开展的Er3+激活中红外激光晶体的相关工作,本文综述了共掺稀土离子对Er3+激活晶体光谱性能的影响:包括敏化离子Cr3+、Yb3+等的敏化作用增强了Er3+的特征吸收峰;退激活离子Pr3+、Ho3+等的退激活效应抑制了自终态瓶颈效应;以及共掺Nd3+所起的敏化和退激活双重作用,并对中红外激光的研究趋势和前景进行了展望。     

Spectroscopic gas analyzers based on indium-phosphide,antimonide and lead-salt diode-lasers

Currently available semiconductor lasers for spectroscopy in the near- and mid-infrared region based on direct band-to-band transitions as gallium-arsenide, indium-phosphide, antimonides and lead-salt containing compounds will be discussed together with the main features of different tunable diode-laser absorption spectrometers for trace gas analysis. Measurements of atmospheric carbon dioxide with a room-temperature 2 microm indium-phosphide laser, applications of antimonide lasers for methane and formaldehyde sensing in the 3-4 microm range and a fast chemical sensor for methane flux measurements based on lead-salt diode-lasers operating near 7.8 microm will be presented.     

Novel Helmholtz-based photoacoustic sensor for trace gas detection at ppm level using GaInAsSb/GaAlAsSb DFB lasers

A new and compact photoacoustic sensor for trace gas detection in the 2-2.5 microm atmospheric window is reported. Both the development of antimonide-based DFB lasers with singlemode emission in this spectral range and a novel design of photoacoustic cell adapted to the characteristics of these lasers are discussed. The laser fabrication was made in two steps. The structure was firstly grown by molecular beam epitaxy then a metallic DFB grating was processed. The photoacoustic cell is based on a Helmholtz resonator that was designed in order to fully benefit from the highly divergent emission of the antimonide laser. An optimized modulation scheme based on wavelength modulation of the laser source combined with second harmonic detection has been implemented for efficient suppression of wall noise. Using a 2211 nm laser, sub-ppm detection limit has been demonstrated for ammonia.     

Molecular two-photon spectroscopy with two synchronized tunable dye lasers

Two tunable dye lasers, with differing wavelength and polarization, were synchronized to produce a two-photon spectrum in gas phase benzene. Simultaneous absorption of two photons from one laser beam was precluded by choosing appropriate wavelengths. All possible ratios have been measured for a totally-symmetric two-photon transition demonstrating a strong analogy between two-photon absorption and Raman scattering.     

High precision measurements of atmospheric nitrous oxide and methane using thermoelectrically cooled mid-infrared quantum cascade lasers and detectors

A compact, fast response, mid-infrared absorption spectrometer using thermoelectrically (TE) cooled pulsed quantum cascade (QC) lasers and TE detectors has been developed to demonstrate the applicability of QC lasers for high precision measurements of nitrous oxide and methane in the earth's atmosphere. Reduced pressure extractive sampling with a 56 m path length, 0.5 l volume, multiple pass absorption cell allows a time response of <0.1s which is suitable for eddy correlation flux measurements for these gases. Precision of 0.3 ppb (rms, 1s averaging time) or 0.1% of the ambient concentration for N(2)O (4 ppb or 0.2% of ambient for CH(4)), has been demonstrated using QC lasers at 4.5 microm (7.9 microm for CH(4)), corresponding to an absorbance precision of 4 x 10(-5) Hz(-1/2) (8 x 10(-5) Hz(-1/2) for CH(4)). Stabilization of the temperature of the optical bench and the pulse electronics results in a minimum Allan variance corresponding to 0.06 ppb for N(2)O with an averaging time of 100 s (0.7 ppb with an averaging time of 200 s for CH(4)). The instrument is capable of long-term, unattended, continuous operation without cryogenic cooling of either laser or detector.     

Generation of High Peak Power Mode-Locked Green Pulses Based on WS2 and EOM: Experiment and Theory

Based on an as-prepared high-quality WS₂ film and an electro-optic modulator (EOM), a dual-loss-modulated low repetition rate mode-locking laser at 0.53 μm with high peak power is presented for the first time. The laser characteristics versus the pump power are investigated experimentally and theoretically. At a pump power of 10.67 W, the shortest pulse duration of 305 ps can be measured, corresponding to the highest peak power of 931 kW, which is much higher than those of the single passive modulated lasers with WS₂-SA. A simple rate equation simulation was used to describe this dual-loss-modulated mode-locking green laser based on WS₂ and EOM. The results of the numerical simulation are basically in accordance with the experimental values.     

Investigation of Nonlinear Optical Modulation Characteristics of MXene VCrC for Pulsed Lasers

We report the surface morphology and the nonlinear absorption characteristics of MXene VCrC nanosheets prepared by the liquid-phase exfoliation method. The self-made MXene VCrC was applied as a saturable absorber in the Tm:YAP laser experiments, performing excellent Q-switching optical modulation characteristics in infrared range. With this absorber, a stable passively Q-switched 2 μm laser was achieved. Under an incident pump power of 3.52 W, a maximum output power of 280 mW was obtained with a T = 3% output coupler at a repetition frequency of 49 kHz. The corresponding pulse energy and peak power were 5.7 μJ and 6.6 W, respectively. The shortest pulse duration was 658 ns at the repetition rate of 63 kHz with a T = 1% output coupler.     

Highly Stable Passively Q-Switched Erbium-Doped All-Fiber Laser Based on Niobium Diselenide Saturable Absorber

A saturable absorber (SA) based on niobium diselenide (NbSe₂), which is a layered transition metal dichalcogenide (TMD) in the VB group, is fabricated by the optically driven deposition method, and the related nonlinear optical properties are characterized. The modulation depth, saturable intensity, and nonsaturable loss of the as-prepared NbSe₂ nanosheet-based SA are measured to be 16.2%, 0.76 MW/cm², and 14%, respectively. By using the as-fabricated NbSe₂ SA, a highly stable, passively Q-switched, erbium-doped, all-fiber laser is realized. The obtained shortest pulse width is 1.49 μs, with a pulse energy of 48.33 nJ at a center wavelength of 1560.38 nm. As far as we know, this is the shortest pulse duration ever obtained by an NbSe₂ SA in a Q-switched fiber laser.     

Characterization of InAlAs/InGaAs/InP mid-infrared quantum cascade lasers

A mid-infrared laser characterization system, including a GPIB programmable I-P and I-V set-up based on direct waveform measurement with extraordinary wide pulse duration and duty cycle tuning range, in conjunction with a Fourier transform infrared spectroscopy system adapted with double modulation technique, has been developed. Based on this characterization system, the characteristics of gas source MBE grown InAlAs/InGaAs/InP quantum cascade lasers (QCL), especially their thermal property, have been evaluated. The results show that in the combination of I-P, I-V and spectral measurements at various driving pulse parameters, the thermal resistance, lasing conditions as well as spectral characteristics of the mid-infrared QCL could be deduced. This characterization system is also a useful tool for the evaluation of other types of diode lasers in the mid-infrared band.     

A Novel Glass Fiber Coated with Sol–Gel Poly-Diphenylsiloxane Sorbent for the On-Line Determination of Toxic Metals Using Flow Injection Column Preconcentration Platform Coupled with Flame Atomic Absorption Spectrometry

A novel simple and sensitive, time-based flow injection solid phase extraction system was developed for the automated determination of metals at low concentration. The potential of the proposed scheme, coupled with flame atomic absorption spectrometry (FAAS), was demonstrated for trace lead and chromium(VI) determination in environmental water samples. The method, which was based on a new sorptive extraction system, consisted of a microcolumn packed with glass fiber coated with sol–gel poly (diphenylsiloxane) (sol–gel PDPS), which is presented here for the first time. The analytical procedure involves the on-line chelate complex formation of target species with ammonium pyrrolidine dithiocarbamate (APDC), retention onto the hydrophobic sol–gel sorbent coated surface of glass fibers, and finally elution with methyl isobutyl ketone prior to atomization. All main chemical and hydrodynamic factors, which affect the complex formation, retention, and elution of the metal, were optimized thoroughly. Furthermore, the tolerance to potential interfering ions appearing in environmental samples was also explored. Enhancement factors of 215 and 70, detection limits (3 s) of 1.1 μg·L⁻¹ and 1.2 μg·L⁻¹, and relative standard deviations (RSD) of 3.0% (at 20.0 μg·L⁻¹) and 3.2% (at 20.0 μg·L⁻¹) were obtained for lead and chromium(VI), respec tively, for 120 s preconcentration time. The trueness of the developed method was estimated by analyzing certified reference materials and spiked environmental water samples.     

Fourier transform Raman spectroscopy: A comparison of Nd:YAG and lower-frequency sources

Fourier transform Raman instruments invariably incorporate Nd:YAG solid state lasers operating at 1064 nm. Recently, new lasers have appeared which are likely to be of appropriate power and linewidth for Raman spectroscopy and to be very economical. They emit at various wavelengths between the deep red and one micron wavelength. We have investigated whether sources in this domain are as satisfactory as Nd:YAG ones and conclude that where samples display even the slightest fluorescence with 1064 nm excitation this will be worse if shorter wavelength sources are used and unacceptably so if the source is of shorter wavelength than 900 nm. Thus as a routine analytical tool new improved sources are essential and many of the newer sources are unlikely to be satisfactory.     

Fabrication of an Anti-Reflective Microstructure on ZnS by Femtosecond Laser Bessel Beams

As an important mid-infrared to far-infrared optical window, ZnS is extremely important to improve spectral transmission performance, especially in the military field. However, on account of the Fresnel reflection at the interface between the air and the high-strength substrate, surface optical loss occurs in the ZnS optical window. In this study, the concave antireflective sub-wavelength structures (ASS) on ZnS have been experimentally investigated to obtain high transmittance in the far-infrared spectral range from 6 μm to 10 μm. We proposed a simple method to fabricate microhole array ASS by femtosecond Bessel beam, which further increased the depth of the microholes and suppressed the thermal effects effectively, including the crack and recast layer of the microhole. The influence of different Gaussian and Bessel beam parameters on the microhole morphology were explored, and three ASS structures with different periods were prepared by the optimized Bessel parameters. Ultimately, the average transmittance of the sample with the ASS microhole array period of 2.6 μm increased by 4.1% in the 6 μm to 10 μm waveband, and the transmittance was increased by 5.7% at wavelength of 7.2 μm.     

Ultra-sensitive mid-infrared evanescent field sensors combining thin-film strip waveguides with quantum cascade lasers

We demonstrate ultra-sensitive chemical sensing in the mid-infrared spectral regime with a combination of quantum cascade lasers (QCLs) with GaAs/Al(0.2)Ga(0.8)As strip waveguides fabricated via metal-organic vapor-phase epitaxy (MOVPE) and reactive ion etching (RIE) using evanescent field absorption spectroscopy. These strip waveguides have been designed with a width of 200 μm, thereby facilitating 2-D confinement and mode-matched propagation of mid-infrared radiation emitted from a distributed feedback (DFB) QCL at a wavelength of 10.3 μm. Acetic anhydride was detected with a limit of detection (LOD) of 18 pL (19.4 ng) deposited at the waveguide surface by overlapping of the vibrational absorption of the methyl group with the emission frequency of the QCL. The obtained results indicate a remarkable enhancement in sensitivity by three orders of magnitude compared to previously reported multimode planar silver halide waveguides. Further reduction of the waveguide strip width to 50 μm resulted in an additional sensitivity enhancement yielding a calculated LOD of 0.05 pL for the exemplary analyte acetic anhydride, which is among the most sensitive evanescent field absorption measurements with a miniaturized mid-infrared sensor system reported to date.