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A laser frequency-locked hollow waveguide (HWG) gas sensor is demonstrated for simultaneous measurements of three isotopologues (12CO2, 13CO2, and 18OC16O) using wavelength modulation spectroscopy with a 2.73 μm distributed feedback laser. The first harmonic (1f) signal at the sampling point where the peak of the second harmonic (2f) signal was located was employed as the locking point to lock the laser frequency to the transition center of 13CO2, while the absorption lines of 12CO2 and 18OC16O were being scanned. Continuous measurements of the three isotopologues of 4.7% CO2 samples over 103 min under free running and frequency locking conditions were performed. The measurement accuracy and precision of the three isotopologues achieved under the frequency locking condition were at least 3 times and 1.3 times better than those obtained under the free running condition, respectively. The Allan variance plot of the developed laser-locked HWG gas sensor shows a detection limit of 0.72‰ for both δ13C and δ18O under the frequency locking condition with a long stability time of 766 s. This study demonstrated the high potential of a novel human breath diagnostic sensor for medical diagnostic with high accuracy, precision, and sensitivity and without frequently repeated calibration.

Novel cross-coupled dual-band bandpass filters (BPFs) with compact size are proposed based on dual-mode isosceles right-angled triangular (IRAT) resonators. The dominant mode in the IRAT resonator is the TM100Z mode. By introducing posts in the resonators, an LC resonant unit is formed, which resonates at a lower frequency than the TM100Z mode. In the design of novel dual-band filters, the LC mode constitutes the first passband while the TM100Z mode produces the second passband. As cross-coupling is applied, two and eight transmission zeros (TZs) are produced in the responses of third-order and fourth-order dual-band BPFs, respectively. Two third-order cross-coupled dual-band BPFs with altered passbands and one fourth-order cross-coupled dual-band BPF are fabricated and measured. The measured results agree very well with the simulated results, demonstrating attractive advantages of the proposed BPFs such as compact size and decent performance.

Yb3+-doped YMgB5O10 (Yb:YMB) crystals with better crystalline quality were grown successfully using the optimized flux of Li2O–B2O3–LiF instead of the traditional K2O3–MoO3 flux by the top-seeded solution growth method. The systematic investigation of the crystal growth, structure characteristics, polarized absorption and emission spectra, fluorescence decay curve and laser properties of the Yb:YMB crystal was reported for the first time. The main spectroscopic and laser parameters, such as the absorption coefficients and cross-sections, energy level schema and barycenter plot, radiative and fluorescence lifetime, emission and gain cross-sections, minimum inversion fraction, pump saturation intensity and minimum absorbed pump intensity, have been calculated and analysed in detail. The broad absorption band (FWHM, 18.4 nm, E//Z) at around 936 nm matches very well with the emission wavelength of InGaAs laser diodes. The intense spectra anisotropy and multi-wavelength emission characteristics make it possible to realize the multi-wavelength laser operation at about 1 μm. The dual-wavelength Yb:YMB laser working at 1036 and 1062 nm with a maximum output power of 3.02 W and a slope efficiency of 46.9% was achieved, which may be a potential light source for THz generation with a large frequency difference of 7.1 THz. The results reveal that Yb:YMB is a promising multi-wavelength laser crystal.

Due to the inherent hysteresis characteristics of the smart material, the positioning accuracy of the piezo-driven manipulator was always decreased. Especially in multi-degrees-of-freedom (MDOFs) compliant manipulators driven by multismart actuators, the cross-coupled hysteresis among MDOFs decreased the positioning accuracy of such compliant platforms significantly. In this paper, the hysteresis feature identification and coupled hysteresis compensation of a piezo-driven XY manipulator was investigated. To establish the hysteresis characteristics of the piezo-driven manipulator, a modified Bouc–Wen model has been proposed, and a Genetic Algorithm-based Particle Swarm Optimization (GA-PSO) was adopted to recognize the parameters of the model. To improve the output performances of the manipulator, the decoupling controller of the XY micromanipulator was designed, and the driven voltages were modified using the estimated coupling displacements. The experiments validated that the modified Bouc–Wen model featured the ability to present the hysteresis process effectively, and the maximum prediction errors are 0.19 μm and 0.16 μm in the two directions separately. The coupled hysteresis displacement before and after implementing the decoupling controller in the X-direction was reduced from 0.56 μm to 0.15 μm, and the coupling effect is reduced by 73.2%, while in the Y-direction, the coupling effect was also decreased by 72.9%.

Tunable diode laser absorption spectroscopy (TDLAS) based on a multipass cell (MPC) is a powerful analytical tool and is widely applied to air quality monitoring, industrial process control, and medical diagnostics. However, the conventional MPC as a core component in TDLAS devices has a large size, low utilization efficiency of the mirror surfaces, and tight optical alignment tolerances. In this paper, we design and fabricate a mini-MPC with an optical absorption path length of 4.2 m and dimensions of 4 × 4 × 6 cm3 (open cavity), which, to our best knowledge, is the current smallest MPC in terms of the same optical path length. The mini-MPC generates a seven-nonintersecting-circle dense spot pattern on two 25.4 mm spherical mirror surfaces, providing a high fill factor of 21 cm-2. A fiber-coupled collimator and an InGaAs photodetector are integrated into the mini-MPC via a high-resolution three-dimensional printed frame, hence removing the requirement of active optical alignment. Using a 1.65 μm distributed-feedback laser, the performance of this mini-MPC for methane detection was evaluated in terms of linearity, flow response time, stability, minimum detectable limit, and measurement precision. Continuous measurements of methane near a sewer and in the atmosphere were performed to demonstrate the stability and robustness of the highly integrated mini-MPC-based gas sensor. Our analysis shows that a methane minimum detectable limit of 117 ppbv is achieved, paving the way toward a sensitive, low-cost, and miniature trace gas sensor inherently suitable for large-scale deployment of distributed sensor networks and for handheld mobile devices.

International audience; Sub-100 fs pulse generation from a passively mode-locked Tm,Ho-codoped cubic multicomponent disordered garnet laser at ∼2 µm is demonstrated. A single-walled carbon nanotube saturable absorber is implemented to initiate and stabilize the soliton mode-locking. The Tm,Ho:LCLNGG (lanthanum calcium lithium niobium gallium garnet) laser generated pulses as short as 63 fs at a central wavelength of 2072.7 nm with an average output power of 63 mW at a pulse repetition rate of ∼102.5 MHz. Higher average output power of 121 mW was obtained at the expense of longer pulse duration (96 fs) at 2067.6 nm using higher output coupling. To the best of our knowledge, this is the first report on mode-locked operation of the Tm,Ho:LCLNGG crystal.

We report on the first sub-100 fs mode-locked laser operation of a Tm3+-doped disordered calcium lithium tantalum gallium garnet (Tm:CLTGG) crystal. Soliton mode-locking was initiated and stabilized by a transmission-type single-walled carbon nanotube saturable absorber. Pulses as short as 69 fs were achieved at a central wavelength of 2010.4 nm with an average power of 28 mW at a pulse repetition rate of ∼87.7 MHz. In the sub-100 fs regime, the maximum average output power amounted to 103 mW.

We report on the first passively mode-locked femtosecond-laser operation of a disordered Yb:Ca3Gd2(BO3)4 crystal using a SEmiconductor Saturable Absorber Mirror (SESAM). Pumping with a single-transverse mode fiber-coupled laser diode at 976 nm, nearly Fourier-transform-limited pulses as short as 96 fs are generated at 1045 nm with an average output power of 205 mW and a pulse repetition rate of ~67.3 MHz. In the continuous-wave regime, high slope efficiency up to 59.2% and low laser thresholds down to 25 mW are obtained. Continuous wavelength tuning between 1006–1074 nm (a tuning range of 68 nm) is demonstrated. Yb:Ca3Gd2(BO3)4 crystals are promising for the development of ultrafast lasers at ~1 μm.

A monoclinic 0.86 at.% Ho3+:MgWO4 crystal is grown by the Top-Seeded-Solution Growth method. Its spectroscopic properties are studied with polarized light for E || a, b, c. The Ho3+ ion transition probabilities are determined within the modified Judd-Ofelt theory (mJ-O) accounting for the configuration interaction. The intensity parameters are Ω2 = 21.09, Ω4 = 4.42, Ω6 = 2.28 [10–20 cm2] and α = 0.053 [10-4 cm]. The calculated radiative lifetime of the 5I7 state is 6.18 ms. The Stark splitting of the 5I7 and 5I8 multiplets is determined with low-temperature spectroscopy. The absorption, stimulated-emission (SE) and gain cross-sections for the 5I8 ↔ 5I7 transition are derived. Ho3+:MgWO4 features a large Stark splitting of the ground-state (380 cm-1), high maximum σSE of 1.82 × 10–20 cm2 at 2.083 μm, broad gain spectra and high luminescence quantum yield making it suitable for efficient continuous-wave and mode-locked lasers at ∼2.1 μm. First laser operation of Ho3+:MgWO4 crystal is demonstrated at 2.104 μm reaching a slope efficiency of 72%.

The development of a fast in situ optical sensor based on a continuous-wave quantum cascade laser operating at 8 μm for the measurement of environmental gaseous nitrous acid (HONO) is reported. A strong absorption line at 1252.2109 cm–1 is found to be free of interferences and used for the first time for ambient HONO detection. Loss of HONO on the wall of the gas sample absorption cell is evaluated. The resulting 1-s detection limit for HONO is 110 pptv with a folded path length of 172 m. Continuous monitoring of HONO and NO2 mixing ratios variations along with the basic meteorological parameters was performed during a field campaign of several days. Typical photochemical reactions of HONO have been observed on sunny and snowy days. Atmospheric HONO mixing ratios observed in this study indicate that direct emission from traffic exhausts and local heterogeneous reactions is potentially important sources of HONO.

A novel solid-solution garnet Yb3+ doped Y3Al5O12 Mn3Al2(SiO4)3 (Yb:YAG-MnASG) has been designed and grown for the first time. The polycrystalline materials, crystal growth, crystal structures, absorption and emission spectra, energy level schema, fluorescence lifetime and laser performance parameters were investigated in detail. Owing to the inhomogeneity in the local environment of Yb3+ caused by the cationic substitutions of Mn2+ for Y3+, Si4+ for Al3+ and high crystal-field strengths caused by distorted host sites, both of the absorption and emission spectral bandwidth of Yb:YAG-MnASG crystal are broadened compared with Yb:YAG. The maximal full width at half maximum (FWHM) of absorption spectra around 940 nm and emission spectra around 1030 nm for Yb:YAG-MnASG crystal are almost 1.2 and 2.5 times larger than those of Yb:YAG crystal, respectively. The results reveal that the novel solid-solution garnet Yb:YAG-MnASG is an excellent candidate for ultrafast pulse laser crystal.

Kerr-lens mode-locked solid-state laser operation at ∼ 2 µ m is investigated. Using a T m 3 + -doped ( L u , S c ) 2 O 3 “mixed” sesquioxide ceramic as a gain medium, pulses as short as 58 fs are generated at ∼ 2081 n m via soft-aperture Kerr-lens mode locking. The average output power amounts to 220 mW at a pulse repetition rate of 84.8 MHz. The emitted spectrum at the long-wavelength wing extends to > 2.2 µ m which is attributed to vibronic transitions of the T m 3 + ions. The latter is found to be essential for generating pulses with durations in the 50 fs range.

A transportable laser heterodyne radiometer (LHR) based on an external cavity quantum cascade laser, operating in the mid-infrared (mid-IR) around 8 µm, was developed for ground-based remote sensing of multiple greenhouse gases. A newly available novel flexible mid-IR polycrystalline fiber was first exploited to couple solar radiation, real-time captured using a portable sun-tracker, to the LHR receiver. Compared to free space coupling of sunlight, the technique usually used nowadays in the mid-IR, such fiber coupling configuration makes the LHR system readily more stable, simpler, and robust. Operation of the LHR with quasi-shot-noise limited performance was analyzed and experimentally achieved by optimizing local oscillator power. To the best of our knowledge, no such performance approaching the fundamental limit has been reported for a transportable LHR operating at a long mid-IR wavelength around 8 µm. C H 4 and N 2 O were simultaneously measured in the atmospheric column using the developed mid-IR LHR. The experimental LHR spectrum of C H 4 and N 2 O was compared and is in good agreement with a referenced Fourier-transform infrared spectrum from the Total Carbon Column Observing Network observation site and with a simulation spectrum from atmospheric transmission modeling.

Cabozantinib is a potent inhibitor of tyrosine kinase receptor that plays key role in tumor pathogenesis. Cabozantinib has been approved by U. S. Food and Drug Administration for the treatment of cancer. The present work was aimed to explore the in vitro metabolism of cabozantinib using liver microsomes and hepatocytes from animal species and humans through ultra-high performance liquid chromatography coupled to quadrupole/orbitrap high resolution mass spectrometer. The metabolites were characterized by their elemental compositions, MS and MS/MS spectra. As a result, a total of 26 metabolites were identified, and 15 metabolites were newly reported. Among these metabolites, M12 (oxidative defluorination), M19 and M22 (demethylation), M21 (hydroxylation) and M26 (N-oxygenation) were the major metabolites in all species. Our data revealed that cabozantinib was metabolized via the following pathways: oxidative defluorination, hydroxylation, amide hydrolysis, O-dealkylation, N-oxygenation, demethylation and glucuronidation. Human recombinant cytochrome P450 (CYP) enzyme analysis revealed that metabolism of cabozantinib was mainly catalyzed by CYP3A4, while other CYP enzymes played negligible role. The current study provided valuable metabolic data of cabozantinib from different animal species and humans, which would aid in safety and efficacy assessment.

Yb 3+ (Yb)-doped monoclinic oxoborates Ca 4 REO(BO 3 ) 3 where RE stands for Gd or Y (denoted as GdCOB and YCOB, respectively) feature the advantages of extremely flat and smooth gain profile due to the significant inhomogeneous broadening related to their disordered structure, large ground state splitting of >1000 cm -1 , good thermo-optic properties as well as polarized emission due to the natural birefringence (acentric monoclinic symmetry), which makes them attractive for the development of tunable and sub-100-fs solid-state lasers in the 1-μm spectral region [1] - [3] and self-frequency doubling. In mixed Yb:Ca 4 Gd x Y 1-x O(BO 3 ) 3 (shortly Yb:GdYCOB) crystal with a partial substitution of Y 3+ by Gd 3+ ions is expected to provide additional broadening of the spectral bands due to the compositional disorder [4] , [5] . Here, we report on a Kerr-lens mode-locked (KLM) operation of Yb:GdYCOB laser generating pulses as short as 43 fs with an average power of 84 mW at 1036.5 nm and a pulse repetition rate of ~70 MHz.

Thulium (Tm 3+ )- and holmium (Ho 3+ )- codoped tetragonal calcium rare-earth aluminates CaLnAlO 4 where Ln stands for Gd and Y (denoted as CALGO and CALYO, respectively) feature the advantages of broad and smooth gain spectra due to the significant inhomogeneous broadening in the K 2 NiF 4 -type disordered structure, good thermal and thermo-optical properties of the host crystals as well as polarized emission due to the natural birefringence, which make them attractive for the development of tunable and sub-100 fs solid-state lasers in the 2-μm spectral region [1] - [4] . While the isostructural host CaLuAlO 4 was never been successfully grown, mixed Tm,Ho:Ca(Gd 1-x Lu x )AlO 4 (shortly Tm,Ho:CALGLO) crystals with a partial substitution of Gd 3+ by Lu 3+ are expected to provide additional broadening of the spectral bands due to the compositional disorder. Here, we report on a semiconductor saturable-absorber mirror (SESAM) mode-locked (ML) Tm,Ho:CALGLO crystalline laser generating pulses as short as 47 fs with an average power of 121 mW at 2033 nm.

Financial inclusion has become an important development strategy in many countries, and related research is increasing. Financial inclusion in China has had significant progress recently. It has gradually formed a unique and sustainable development path with supporting policies and regulations as well as rapid development and application of digital technology. While challenges remain, the experience of Chinese financial inclusion provides valuable lessons and research directions for policymakers and researchers.

Laser heterodyne spectroscopic measurement technique[1] has been proved to be a powerful and effective remote sensing tool for measurements of greenhouse gases in the atmospheric column[2-6]. In the present work, we report the development of a portable all-fiber coupled dual-channel laser heterodyne radiometer (LHR) and its field deployment. Two DFB lasers operating at 1650.9 nm and 1603.6 nm are used for the remote measurements of column CH4 and CO2, respectively. A fiber optic switch is used to modulate and split the collected sunlight into two channels for simultaneous measurements of both target greenhouse gases. Custom-made preamplifiers combined with digital lock-in amplifiers are used to extract the laser heterodyne signals. The spectral resolution of the instrument is about 0.00442 cm-1, and the signal-to-noise ratio of the measured spectrum of about 250 is achieved with 0.8 s average time per sampling datum. The developed LHR instrument was successfully deployed to a field atmospheric observation experiment (in Dachaidan district, Qinghai province, China).The experimental detail including the LHR instrument integration, dual-channel measurement results of column CH4 and CO2 and preliminary data inversion results will be presented and discussed.Acknowledgments. The project was supported by the national key R&D program of China (2017YFC0209705). The authors thank the financial supports from the CPER CLIMIBIO program, the Labex CaPPA project (ANR-10-LABX005).References[1] D. Weidmann, T. Tsai, N. A. Macleod, G. Wysocki, Opt. Lett. 36 (2011) 1951-1953.[2] E. L. Wilson, A. J. DiGregorio, G. Villanueva, C. E. Grunberg, et al., Appl. Phys. B 125 (2019) 211-219.[3] D. S. Bomse, J. E. Tso, M. M. Flors, J. H. Miller, Appl. Opt. 59 (2020) B10-B17.[4] J. Wang, G. Wang, T. Tan, G. Zhu, C. Sun, Z. Cao, W. Chen, X. Gao, Opt. Express 27 (2019) 9610-9619[5] A. Rodin, A. Klimchuk, A. Nadezhdinskiy, D. Churbanov, et al., Opt. Express 22 (2014) 13825-13834.[6] E. L. Wilson, M. L. McLinden, J. H. Miller, H. R. Melroy, et al., Appl. Phys. B 114 (2014) 385-393.

Tunable diode laser absorption spectroscopy (TDLAS) based on multi-pass cell (MPC) [1-4] is a powerful analytical tool for field applications in air quality monitoring, industrial process control and medical diagnostics. However, the conventional MPC as a core component in TDLAS devices has a large size, low utilization efficiency of the mirror surfaces and tight optical alignment tolerances [5]. Design of miniaturized long-path MPC for the development of handheld portable high sensitivity sensing devices is one of the mainstream trends nowadays. In this work, we designed and fabricated a mini-MPC with an effective optical absorption path length of 4.2 m and dimensions of 4×4×6 cm3, which to our best knowledge is the current smallest MPC in terms of the same optical path length. The mini-MPC generates a seven-nonintersecting-circle dense spot pattern on two 25.4 mm spherical mirror surfaces providing a high fill factor of 21 cm-2. A fiber-coupled collimator and an InGaAs photodetector are integrated into the mini-MPC via a high-resolution 3D-printed frame, hence removing the requirement of active optical alignment. Using a 1.65 μm distributed-feedback laser, the performance of this mini-MPC for methane detection was evaluated in terms of linearity, flow response time, stability, minimum detectable limit and measurement precision. Continuous measurements of methane near a sewer and in the atmosphere were performed to demonstrate the stability and robustness of the highly integrated mini-MPC based gas sensor. This work paves the way towards a sensitive, low-cost, miniature trace gas sensor inherently suitable for large-scale deployment of distributed sensor networks and for handheld mobile devices.AcknowledgmentsThe project is sponsored by National Key R&D Program of China (2017YFA0304203), National Natural Science Foundation of China (NSFC) (61622503, 61575113, 61805132, 11434007), Outstanding Innovative Teams of Higher Learning Institutions of Shanxi, Foundation for Selected Young Scientists Studying Abroad, Sanjin Scholar (2017QNSJXZ-04) and Shanxi “1331KSC”. Frank K. Tittel acknowledges support by the Robert Welch Foundation (Grant #C0586).References[1] L. Dong; F. K. Tittel; C. Li; N. P. Sanchez; H. Wu; C. Zheng, Y. Yu, A. Sampaolo, R. J. Griffin, Opt. Express 24 (2016) A528.[2] K. Liu, L. Wang, T. Tan, G. S. Wang, W. J. Zhang, W. D. Chen, X. M. Gao, Sensor. Actuat. B-Chem. 220 (2015) 1000.[3] R. Cui, L. Dong, H. Wu, S. Li, L. Zhang, W. Ma, W. Yin, L. Xiao, S. Jia, F. K. Tittel, Opt. Express 26 (2018) 24318.[4] C. T. Zheng, W. L. Ye, J. Q. Huang, T. S. Cao, M. Lv, J. M. Dang, Y. D Wang, Sensor. Actuat. B-Chem. 190 (2014) 249.[5] P. Weibring, D. Richter, A. Fried, J. G. Walega, C. Dyroff, Appl. Phys. B 85 (2006) 207.

Monoclinic ytterbium-lithium codoped zinc monotungstate crystal (Yb3+,Li+:ZnWO4) is a promising material for laser opertation at ~1.06 μm. Absorption, σabs, and stimulated-emission, σSE, cross-sections are determined for light polarized along the optical indicatrix axes, E || Np, Nm and Ng. At room temperature, the maximum σSE amounts to 2.81 × 10−20 cm2 at 1055.6 nm (for E || Np) and the gain bandwidth reaches ~22 nm (for E || Ng). The radiative lifetime of the upper laser level is 0.37 ms. The Stark splitting of Yb3+ multiplets is resolved with low-temperature (6 K) spectroscopy revealing a relatively large total splitting of the ground-state, ΔE(2F7/2) = 804 cm−1, being remarkably high as compared to other Yb3+-doped tungstate crystals. A notable inhomogeneous broadening of the zero-phonon line is detected at 6 K. A continuous-wave diode-pumped 1.8 at.% Yb3+,Li+:ZnWO4 laser generated a maximum output power of 2.90 W at ~1059 nm with a slope efficiency of 57.9% and a linearly polarized output (E || Np). Yb3+,Li+:ZnWO4 is attractive for broadly tunable and mode-locked oscillators.

We report on the growth, structure refinement, optical spectroscopy, continuous wave and femtosecond mode-locked laser operation of a Tm3+,Ho3+-codoped disordered calcium niobium gallium garnet (CNGG) crystal. The 2.64 at.% Tm, 0.55 at.% Ho:CNGG is grown by the Czochralski method. Its cubic structure, sp. gr. I a 3 ¯ d - O10h, a = 12.4952(1) A, is refined by the Rietveld method revealing a random distribution of Ga3+ and Nb5+ cations over octahedral and tetrahedral sites. The Ho3+ transition probabilities are determined within the Judd-Ofelt theory accounting for an intermediate configuration interaction (ICI). For the 5I7 → 5I8 Ho3+ transition, the maximum stimulated-emission cross-section σSE is 0.47 × 10−20 cm2 at 2080.7 nm. The gain bandwidth of Tm,Ho:CNGG at ∼2 μm is > 150 nm and the thermal equilibrium decay time - 6.80 ms. The Tm3+ ↔ Ho3+ energy transfer parameters are determined. A diode-pumped Tm,Ho:CNGG microchip laser generated 413 mW at 2088.4 nm with a slope efficiency of 15.9%. A continuous wavelength tuning between 1940.3 and 2144.6 nm is demonstrated. Ultrashort pulses as short as 73 fs are achieved at 2061 nm from a Tm,Ho:CNGG laser mode-locked by a GaSb semiconductor saturable absorber mirror at a repetition rate of 89.3 MHz.

This publisher’s note corrects the authors’ affiliations in Photon. Res. 9, 357 (2021)PRHEIZ2327-912510.1364/PRJ.413276.

We report on a purely Kerr-lens mode-locked Tm:(Lu,Sc)2O3 ceramic laser emitting at 2083 nm. Nearly Fourier-transform-limited 58-fs pulses are generated with an average output power of 220 mW at a repetition rate of 84.8 MHz.

We report on a power-scalable sub-100-fs laser in the 2-μm spectral range using a Tm3+-doped ‘mixed’ (Lu,Sc)2O3 sesquioxide ceramic as an active medium. Pulses as short as 58 fs at 2076 nm with an average output power of 114 mW at a pulse repetition rate of approximately 82.9 MHz are generated by employing single-walled carbon nanotubes as a saturable absorber. A higher average power of 350 mW at 2075 nm is obtained at the expense of the pulse duration (65 fs). A maximum average power of 486 mW is achieved for a pulse duration of 98 fs and an optical conversion efficiency of 22.3%, representing the highest value ever reported from sub-100-fs mode-locked Tm lasers.

The combination of broadband light sources together with optical cavities has become a valuable atmospheric approach, uniting the selectivity of broad spectra with the sensitivity produced by optical cavities. Concentrations of key atmospheric gases as well as the optical properties of particles are now routinely measured with instruments based on this approach. This chapter gives an introduction to optical cavities and an overview of ringdown, cavity-enhanced, and phase shift measurements using optical cavities with broadband light sources and detectors. Instrument design, calibration approaches, and performance characterization are described. Example applications are presented in a range of measurement environments for NO2, NO3, and N2O5, HONO, glyoxal and methylglyoxal, halogens and their oxides, and several other species of atmospheric importance.

We report on the development of a novel laser crystal with broadband emission properties at ∼2 µm – a Tm3+,Li+-codoped calcium tantalum gallium garnet (Tm:CLTGG). The crystal is grown by the Czochralski method. Its structure (cubic, sp. gr. I a 3 ¯ d , a = 12.5158(0) Å) is refined by the Rietveld method. Tm:CLTGG exhibits a relatively high thermal conductivity of 4.33 Wm-1K-1. Raman spectroscopy confirms a weak concentration of vacancies due to the charge compensation provided by Li+ codoping. The transition probabilities of Tm3+ ions are determined using the modified Judd-Ofelt theory yielding the intensity parameters Ω2 = 5.185, Ω4 = 0.650, Ω6 = 1.068 [10−20 cm2] and α = 0.171 [10−4 cm]. The crystal-field splitting of the Tm3+ multiplets is revealed at 10 K. The first diode-pumped Tm:CLTGG laser generates 1.08 W at ∼2 µm with a slope efficiency of 23.8%. The Tm3+ ions in CLTGG exhibit significant inhomogeneous spectral broadening due to the structure disorder (a random distribution of Ta5+ and Ga3+ cations over octahedral and tetrahedral lattice sites) leading to smooth and broad gain profiles (bandwidth: 130 nm) extending well above 2 µm and rendering Tm:CLTGG suitable for femtosecond pulse generation.

We report on sub-50 fs pulse generation from a passively mode-locked (ML) Tm,Ho-codoped crystalline laser operating in a 2 µm spectral region. A T m , H o : C a ( G d , L u ) A l O 4 laser delivers pulses as short as 46 fs at 2033 nm with an average power of 121 mW at a pulse repetition rate of ∼ 78 M H z employing a semiconductor saturable absorber mirror as a saturable absorber. To the best of our knowledge, this result represents the shortest pulses ever generated from a Tm- and/or Ho-based solid-state laser. Polarization switching in the anisotropic gain material is observed in the ML regime without any polarization selection elements which is essential for the shortest pulses.

In this paper, a miniaturized dual-mode dual-band bandpass filter (BPF) with controllable frequency ratio based on patch-loaded substrate integrated waveguide (PSIW) cavity is proposed. In order to realize the dual-band bandpass filter, two metallized blind vias are introduced along the symmetrical plane to provide an additional mode nominated as LC mode. By utilizing the additional mode and TEM 001 mode in PSIW cavity, dual-band bandpass response is achieved. Moreover, the introduced blind vias can make frequency shifting of LC mode while not affect TEM 001 mode. As a result, the frequency ratio of the two passbands can be controlled. For demonstration, a dual-band filter operating at 1.09 and 3.58 GHz is designed, fabricated and measured. The insertion losses are measured to be 1.24 dB and 2.23 dB with the measured return losses better than 17 dB.

In this paper, we propose a novel convolutional neural network called LightCNN to realize moving maritime targets detection in complex sea environment, which can not only accomplish the detection on targets in short time but also ensure the high detection probability. The proposed network LightCNN has totally five layers with only one convolutional layer. It can automatically extract features from time-frequency images to detect target. Experimental results on the IPIX and CSIR datasets verify that the LightCNN can achieve high detection probability and real-time processing, satisfying the requirement in practical applications in radar field.

Measurement of ambient aerosol and nitrogen dioxide (NO2) is important as they are major pollutants from the burning of fossil fuel and biomass. In the present work, a differential photoacoustic spectrometer (D-PAS) was developed for simultaneous, online measurements of aerosol optical absorption and NO2 concentration. A novel photoacoustic resonator was designed and employed in the D-PAS for controlling a large flow rate, improving response time, and keeping the flow noise at a low level. The detection limits of 1.0 Mm−1 and 0.87 ppb for aerosol absorption and NO2 concentration measurements were achieved with a lock-in amplifier time constant of 1 s. The D-PAS accuracy was demonstrated by performing a long-time, continuous measurement of aerosol, and NO2 in ambient air. The measured results of NO2 are consistent with the NOx analyzer and environmental monitoring station results.

The behavior of directly linearly polarized emission was investigated in an isotropic Nd:YAG laser with a weakly anisotropic Fabry-Perot cavity. In order to explore the polarization mechanism, the intracavity eigenmodes were analyzed theoretically. A theoretical model was developed and shown to be suitable for describing the orientation-dependent beam profiles of the polarizer-specific features observed in experiments. This model indicates that the linear polarization emission results from the coherently combined state of intracavity eigenmodes as opposed to an intrinsic polarization state. The coherent combination is attributed to the frequency degeneracy and spontaneous phase locking of polarized eigenmodes. For the first time, the polarization coupling mechanism based on the coherent combination of eigenmodes in an isotropic solid-state laser was demonstrated. Moreover, this study also contributes an effective method to judge different types of linear polarization states.

A vernier caliper time-to-digital converter (VC-TDC) based on field programmable gate array (FPGA) is proposed in this paper. The VC-TDC consists of a central carry chain and (N-1) auxiliary carry chains. Multichain interpolation method is applied on auxiliary carry chains to get an interpolated chain, which can improve the resolution of VC-TDC without artificially destroying taps of carry chains. To reduce the nonlinearity of multichain interpolated TDC, a twice downsampling method is proposed to downsample central chain and interpolated chain to obtain main scale and vernier scale of VC-TDC. The main scale can greatly reduce the multichain mapping time, and the vernier scale can provide high resolution and high linearity. To evaluate the performance of VC-TDC, 7 auxiliary carry chains and 13 auxiliary carry chains were implemented on Xilinx’s 40nm virtex-6 FPGA. The VC-TDC can achieve resolution of 10ps, maximum RMS precision of 5.5ps, DNL within [-0.07, 0.07], INL within [-0.13, 0.03]. The consistency between experimental results and theoretical analysis shows that the proposed VC-TDC is an effective method to achieve ultralow nonlinearity and high RMS resolution.

Target tracking in sea clutter is always a challenging problem due to the weak target returns, especially in terrible sea conditions. Since the radar returns are frequently submerged by strong clutter, conventional tracking algorithms, which only use the dynamic characteristics of the target like position, speed, etc., failed to achieve satisfying tracking performance. Hence, additional features could be introduced in order to distinguish target and clutter effectively. Specifically, this paper introduces three features in the time domain, frequency domain, and time-frequency domain respectively, and combines them into the conventional Gaussian Mixture Probability Hypothesis Density (GM-PHD) multi-target tracking algorithm. Moreover, we utilize Multiple Hypothesis Tracking (MHT) to manage the track for further improving the tracking results. The experimental results on the CSIR public set verity the effectiveness of the proposed method.

Victim refers to a person whose personal right, property right or other legitimate rights and interests have been infringed upon by criminal acts. There must be a victim or victims in a crime. Before the state and the law were established, the victim has a wide range of rights to punishment onto the offender.

Since human society abandoned blood feud and relief by private force, and entered the era of national criminal procedure, the continuous differentiation of powers and expansion of rights in the realm of criminal procedure has become the main thread of the evolution of the procedural regime.

In criminal proceedings, there are three fundamental litigation functions, including trial, prosecution and defense which are performed by the court, the procuratorial organ and the defendant, respectively, and none of them is allowed to carry out more than one roles.

Real-time measuring of CO2 isotopes (13CO2, 12CO2, and 18OC16O) in exhaled breath using a mid-infrared hollow waveguide gas sensor incorporating a 2.73 μm distributed feedback laser was proposed and demonstrated for the first time based on calibration-free wavelength modulation spectroscopy. The measurement precisions for δ13C and δ18O were, respectively, 0.26 and 0.57‰ for an integration time of 131 s by Allan variance analysis. These measurement precisions achieved in the present work were at least 3.5 times better than those reported using direct absorption spectroscopy and 1.3 times better than those obtained by calibration-needed wavelength modulation absorption spectroscopy. Continuous measurement of three isotopes in the breathing cycle was performed. Alveolar gas from the expirogram was identified, and the 13C/12C and 18O/16O ratios were found to be almost constant during the alveolar plateau, which enables optimization of breath sampling and provides accurate information on metabolic processes. The 13C/12C and 18O/16O isotope ratios at the alveolar plateau of five breath cycles were averaged, yielding δ13C and δ18O values of (-24.3 ± 3.4) and (-30.7 ± 2.6) ‰, respectively. This study demonstrates the feasibility of real-time analysis of 13C- and 18O-isotopes of human breath CO2 in clinical applications and shows its potential for diagnosing respiratory-related diseases with high sensitivity, selectivity, and specificity.

In this article, a compact dual-laser sensor based on an off-axis integrated-cavity output spectroscopy and time-division multiplexing method is reported. A complete dual-channel optical structure is developed and integrated on an optical cavity, which allows two distributed feedback (DFB) lasers operating at wavelengths of 1603 nm and 1651 nm to measure the concentration of CO2 and CH4, simultaneously. Performances of the dual-laser sensor are experimentally evaluated by using standard air (with a mixture of CO2 and CH4). The limit of detection (LoD) is 0.271 ppm and 1.743 ppb at a 20 s for CO2 and CH4, respectively, and the noise equivalent absorption sensitivities are 2.68 × 10−10 cm−1 Hz−1/2 and 3.88 × 10−10 cm−1 Hz−1/2, respectively. Together with a commercial instrument, the dual-laser sensor is used to measure CO2 and CH4 concentration over 120 h and verify the regular operation of the sensor for the detection of ambient air. Furthermore, a first-order exponential moving average algorithm is implemented as an effective digital filtering method to estimate the gas concentration.

[EN]Surface channel waveguides (WGs) based on a half-ring (40–60-µm-diameter) depressed-index cladding (type III) geometry are fabricated in monoclinic Tm3+:MgWO4 by femtosecond (fs) laser writing at a repetition rate of 1 kHz. The WGs are characterized by confocal laser microscopy and 𝜇-Raman spectroscopy. A Tm3+:MgWO4 WG laser generates 320 mW at ∼2.02µm with a slope efficiency of 64.4%. The WG emits a transverse single-mode and linear polarization (𝐸||𝑁𝑚). A remarkable low loss of, Ministerio de Economía y Competitividad (FIS2017-87970-R, MAT2016-75716-C2-1-R (AEI/FEDER, UE)); Agència de Gestió d’Ajuts Universitaris i de Recerca (2017SGR755); Consejería de Educación, Junta de Castilla y León (SA287P18); National Natural Science Foundation of China (51761135115, 61575199, 61850410533, 61875199, 61975208); Ministry of Science and Higher Education of the Russian Federation (Goszadanie 2019-1080); Deutsche Forschungsgemeinschaft (PE 607/14-1).

Measurements of vertical concentration profiles of greenhouse gases (GHGs) is extremely important for our understanding of regional air quality and global climate change trends. In this context, laser heterodyne radiometer (LHR) technique has been developed [1-5] for ground-based remote measurements of GHGs in the atmospheric column.Solar radiation undergoing absorption by multi-species in the atmosphere is coupled into a LHR instrument where the sunlight is mixed with a local oscillator (LO), being usually a tunable laser source, in a fast photodetector. Beating note at radio frequency (RF) resulted from this photomixing contains absorption information of the LO-targeted molecules. Scanning the LO frequency across the target molecular absorption lines allows one to extract the corresponding absorption features from the total absorption of the solar radiation by all molecules in the atmospheric column. Near-IR (~1.5 µm) and mid-IR (~8 µm) [6] LHRs have been recently developed in the present work. Field campaigns have been performed on the roof of the platform of IRENE in Dunkerque (51.05°N/2.34°E).The developed LHR instruments as well as the preliminary results of their applications to the measurements of CH4, N2O, CO2 (including 13CO2/12CO2), H2O vapor (and its isotopologue HDO) in the atmospheric column will be presented and discussed.Acknowledgments The authors thank the financial supports from the LABEX CaPPA project (ANR-10-LABX005), the MABCaM (ANR-16-CE04-0009) and the MULTIPAS (ANR-16-CE04-0012) contracts, as well as the CPER CLIMIBIO program. S. F. thanks the program Labex CaPPA and the "Pôle Métropolitain de la Côte d’Opale" (PMCO) for the PhD fellowship support.References [1] R. T. Menzies, and R. K. Seals, Science 197 (1977) 1275-1277[2] D. Weidmann, T. Tsai, N. A. Macleod, and G. Wysocki, Opt. Lett. 36 (2011) 1951-1953[3] E. L. Wilson, M. L. McLinden, and J. H. Miller, Appl. Phys. B 114 (2014) 385-393[4] A. Rodin, A. Klimchuk, A. Nadezhdinskiy, D. Churbanov, and M. Spiridonov, Opt. Express 22 (2014) 13825-13834[5] J. Wang, G. Wang, T. Tan, G. Zhu, C. Sun, Z. CAO, W. Chen, and X. Gao, Opt. Express 27 (2019) 9600-9619[6] F. Shen, P. Jeseck, Y. Te, T. Tan, X. Gao, E. Fertein, and W. Chen, Geophys. Res. Abstracts, 20 (2018) EGU2018-79

The use of high reflectivity dielectric mirrors to form a high finesse optical cavity allows one to achieve long optical path lengths of up to several kilometres for high-sensitivity spectroscopy applications [1]. However, the high reflectivity of a dielectric mirror is achieved via constructive interference of the Fresnel reflection at the interfaces produced by multilayer coatings of alternate high and low refractive index materials. This wavelength-dependent coating limits the bandwidth of the mirror's high reflectivity to only a few percent of the designed central wavelength [2].In this paper, we report on the development of a novel optical cavity based on prism used as cavity reflector through total internal reflection combined with Brewster angle incidence [3], which offers a high-finesse optical cavity operating in a broadband wavelength region from 400 to longer than 1600 nm. Cavity Enhanced Absorption Spectroscopy (CEAS) of NO2, NO3, and H2O vapor was applied to determine the achieved prism reflectivity over a broad spectral range from 400 nm to 1600 nm.Experimental details and preliminary results will be presented. The developed prism-based cavity is specifically adapted for the needs of broadband measurement of multi-molecular absorber or/and wavelength-dependent extinction coefficient of aerosols over a broad spectral region.Acknowledgments. This work is supported by the French national research agency (ANR) under the CaPPA (ANR-10-LABX-005), the MABCaM (ANR-16-CE04-0009) and the MULTIPAS (ANR-16-CE04-0012) contracts. The authors thank the financial support from the CPER CLIMIBIO program.REFERENCES[1] S. S. Brown, "Absorption spectroscopy in high-finesse cavities for atmospheric studies", Chem. Rev. 103 (2003) 5219-5238.[2] G.R. Fowles, Introduction to Modern Optics, 2nd ed. (Rinehart and Winston, 1975), p. 328.[3] B. Lee, K. Lehmann, J. Taylor and A. Yalin, "A high-finesse broadband optical cavity using calcium fluoride prism retroreflectors", Opt. Express 22 (2014) 11583-11591.

Tm,Ho co-doped disordered calcium niobium gallium garnet (CNGG) crystals are investigated as a novel gain medium for mode-locked lasers near 2 μm. With a GaSb-based semiconductor saturable absorber mirror (SESAM) and chirped mirrors for dispersion compensation such a laser is mode-locked at a repetition rate of 89.3 MHz. For a 5% output coupler, a maximum average output power of 157 mW is obtained with a pulse duration of 170 fs (28-nm broad spectrum centered at 2.075 μm, leading to a time-bandwidth product of 0.331). With a 0.5% output coupler, 73-fs pulses are generated at 2.061 μm with a spectral width of 62 nm (time-bandwidth product of 0.320) and an average output power of 36 mW.

A proof-of-concept gas sensor based on innovative photoacoustic spectrophone was introduced for purpose of developing a low cost and simple configuration photoacoustic spectroscopy gas sensor and demonstrated, in which the photoacoustic signal was detected with a low cost polyvinylidene fluoride (PVDF) film being used as transducer, instead of using conventional microphone or quartz tuning fork. In such a PVDF-based photoacoustic spectroscopy (PVDF-PAS) approach, the PVDF film plays a role both as a cantilever used in cantilever-enhanced photoacoustic spectroscopy and as a piezoelectric quartz tuning fork used in quartz-enhanced photo-acoustic spectroscopy. Feasibility of the introduced PVDF-PAS for trace gas sensing was demonstrated by measuring H2O vapor with a minimum detection limit of 40 ppmv using a lock-in time constant of 30 ms, this corresponding to a normalized noise equivalent absorption coefficient (NNEA) of 2.4 × 10−7 cm-1W/Hz1/2. The use of polyvinylidene fluoride film as transducer for photoacoustic signal sensing offers good flexibility, water resistance, chemical stability and low cost for applications under harsh or/and specific environmental conditions.

In the context of climate change mitigation, reuse of carbon dioxide (CO2) represents an alternative with important applications in chemical industry and power generation. For this purpose, CO2 must be purified. Combustion processes lead to high amounts of CO2 but still with impurities and also accompanied by toxic gases (mainly NO and CO). A catalytic reduction process of NO (to N2) while oxidizing CO into CO2 is a promising method to purify the CO2. However, nitrous oxide (N2O) with a global warming potential of 300 times greater than CO2 may be a by-product from this process. It is therefore necessary to optimize the chemical reaction conditions to minimize N2O production. A room-temperature continuous-wave (CW) external cavity quantum cascade laser (EC-QCL)-based optical sensor was developed for real-time monitoring N2O production during the whole catalytic reaction process. A well-isolated N2O absorption line, located at 1261.0598 cm−1, of the ν1 fundamental vibrational band was selected for sensitive and selective measurement of N2O concentration by direct absorption spectroscopy. Using a modified-Herriot multi-pass cell with an effective path-length of 50 m, the limit of detection (1σ) of 32.3 ppbv was obtained in 12 s with 1.1% relative uncertainty in measurement precision. N2O productions through the catalytic reduction of NO by CO over Pt/SiO2 catalyst under different temperatures were investigated. High N2O production of up to ∼6.1 ppmv at 190 °C was observed. The optimal reaction conditions for zero N2O production were found at a temperature higher than 340 °C where 47% of NO was converted to N2.

Tm3+:Na2La4(WO4)7, a disordered tetragonal scheelite-type tungstate crystal, is grown by the Czochralski method. The polarized absorption, stimulated-emission and gain cross-section spectra are determined. The maximum σSE is 1.62 × 10–20 cm2 at 1788.6 nm for σ-polarization. The Judd-Ofelt parameters for Tm3+ are Ω2 = 10.321, Ω4 = 0.183 and Ω6 = 2.122 [10–20 cm2]. The radiative lifetime of the 3F4 state is 1.63 ms. Raman spectroscopy reveals a maximum phonon energy of 923 cm−1. Laser operation under diode-pumping is achieved with both a-cut and c-cut Tm:Na2La4(WO4)7 crystals, reaching a maximum output power for the a-cut of 715 mW at ~ 1937 nm with a slope efficiency of 34%. Microchip laser operation using the c-cut crystal yields a slope efficiency of 41%. The Tm:Na2La4(WO4)7 crystal is promising for mode-locked lasers due to its broadband emission.

Tm3+-doped monoclinic magnesium monotungstate (MgWO4) is a promising material for lasers emitting at above 2 μm. Stark splitting of 3H6 to 1G4 Tm3+ multiplets in MgWO4 is determined using low-temperature spectroscopy, calculated within crystal-field theory modified for the case of an intermediate configuration interaction (ICI) and analyzed in terms of the barycenter plot. Tm3+:MgWO4 features a large Stark splitting of the ground-state (3H6), 633 cm−1, and high transition cross-sections for polarized light due to its low-symmetry structure. A unique feature of Tm3+:MgWO4 to provide a naturally polarized emission at >2 μm, as well as its suitability for broadly tunable and mode-locked lasers in this spectral range are argued. The first tunable and vibronic Tm3+:MgWO4 lasers are demonstrated, yielding a continuous tuning from 1897 to 2062 nm in the former case. A vibronic laser operated at even longer wavelengths up to 2093 nm due to electron-phonon coupling with low-energy phonons of the crystalline host. Moreover, the optical indicatrix axes of high-refractive-index biaxial MgWO4 are assigned.

A compact laser-based absorption sensor system associated with a 152-m path length absorption cell for simultaneous second harmonic (2f) detection of atmospheric nitrous oxide (N2O), methane (CH4), and water vapor (H2O) is presented. An 8 μm external cavity quantum cascade laser (EC-QCL) was used as an excitation source to simultaneously target three neighboring absorption lines, N2O at 1255.424 cm−1, CH4 at 1255.000 cm−1, and H2O at 1254.732 cm−1. Minimum detection limits (1σ) of 0.9 ppb for N2O, 4.8 ppb for CH4 and 31 ppm for H2O were achieved with a 1-s integration time at an optimum pressure of 50 Torr. Both laboratory and atmospheric environmental mixing ratios of these three gases associated with basic meteorological parameters were recorded and the corresponding emission sources were analyzed. In particular, the N2O emission was studied during extended time periods including rainy intervals.