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| 1 | Broadband mid-infrared molecular spectroscopy based on passive coherent optical–optical modulated frequency combs显示文摘Mid-infrared dual-comb spectroscopy is of great interest owing to the strong spectroscopic features of trace gases,biological molecules,and solid matter with higher resolution,accuracy,and acquisition speed. However,the prerequisite of achieving high coherence of optical sources with the use of bulk sophisticated control systems prevents their widespread use in field applications. Here we generate a highly mutually coherent dual midinfrared comb spectrometer based on the optical–optical modulation of a continuous-wave (CW) interband or quantum cascade laser. Mutual coherence was passively achieved without post-data processes or active carrier envelope phase-locking processes. The center wavelength of the generated mid-infrared frequency combs can be flexibly tuned by adjusting the wavelength of the CW seeds. The parallel detection of multiple molecular species,including C_(2)H_(2),CH_(4),H_(2)CO,H_(2)S,COS,and H_(2)O,was achieved. This technique provides a stable and robust dual-comb spectrometer that will find nonlaboratory applications including open-path atmospheric gas sensing,industrial process monitoring,and combustion. | ZHONG ZUO CHENGLIN GU DAOWANG PENG XING ZOU YUANFENG DI LIAN ZHOU DAPING LUO YANG LIU WENXUE LI | 2021 | Photonics Research2021，9，7： | 3 |
| 2 | Doppler velocimeter based on dual-comb absorption spectroscopy显示文摘The determination of airflow parameters is essential to the research of critical information on environment monitoring,chemical kinetics,and aerodynamic and propulsion applications.During the past few decades,tunable diode laser absorption spectroscopy has become a common and efficient tool for the flow velocity measurement based on the Doppler shift of the absorption line.Dual-comb absorption spectroscopy(DCAS),as a state-of-theart Fourier-transform broadband spectroscopic technique,not only can detect multiple trace molecules in parallel but also can extract Doppler shifts to derive the flow velocity through the analysis of dozens of molecular absorption lines simultaneously with high precision.Here,we report a proof-of-principle demonstration of the velocity measurements of acetylene at various flow velocities by means of a high-resolution and broadband DCAS.Mode-resolved Doppler-shifted rotational-vibrational lines in the P branch of acetylene molecules are obtained.A model for multiline Doppler frequency determination is investigated and experimentally verified.The flow velocity measurements with a measuring uncertainty down to the submeter per second over the range from 8.7 m/s to 44.8 m/s at an effective time resolution of 1 s and a measuring uncertainty of 1.97 m/s at 0.1 s are demonstrated.With broadband mid-infrared frequency combs covering atmospheric transmission windows,the open-path measurement for monitoring diffusion of the weak pollutant source would be realized. | CHENGLIN GU XING ZOU ZHONG ZUO DAOWANG PENG YUANFENG DI YANG LIU DAPING LUO WENXUE LI | 2020 | Photonics Research2020，8，12： | 2 |
| 3 | A Phonetic-Semantic Pre-Training Model for Robust Speech Recognition显示文摘Robustness is a long-standing challenge for automatic speech recognition(ASR)as the applied environment of any ASR system faces much noisier speech samples than clean training corpora.However,it is impractical to annotate every types of noisy environments.In this work,we propose a novel phonetic-semantic pre-training(PSP)framework that allows a model to effectively improve the performance of ASR against practical noisy environments via seamlessly integrating pre-training,self-supervised learning,and fine-tuning.In particular,there are three fundamental stages in PSP.First,pre-train the phone-to-word transducer(PWT)to map the generated phone sequence to the target text using only unpaired text data;second,continue training the PWT on more complex data generated from an empirical phone-perturbation heuristic,in additional to self-supervised signals by recovering the tainted phones;and third,fine-tune the resultant PWT with real world speech data.We perform experiments on two real-life datasets collected from industrial scenarios and synthetic noisy datasets,which show that the PSP effectively improves the traditional ASR pipeline with relative character error rate(CER)reductions of 28.63%and 26.38%,respectively,in two real-life datasets.It also demonstrates its robustness against synthetic highly noisy speech datasets. | Xueyang Wu Rongzhong Lian Di Jiang Yuanfeng Song Weiwei Zhao Qian Xu Qiang Yang | 2022 | CAAI Artificial Intelligence Research2022，1，1： | 0 |
| 4 | Dual-comb spectroscopy from the ultraviolet to mid-infrared region based on high-order harmonic generation显示文摘Dual-comb spectroscopy(DCS)has revolutionized numerous spectroscopic applications due to its high spectral resolution and fast measurement speed.Substantial efforts have been made to obtain a coherent dual-comb source at various spectral regions through nonlinear frequency conversion,where the preservation of coherence has become a problem of great importance.In this study,we report the generation of coherent dual-comb sources covering from the ultraviolet to mid-infrared region based on high-order harmonic generation.Driven by high-repetition-rate femtosecond mid-infrared dual-comb pump pulses,up to ninth-order harmonic was generated from the ultraviolet to mid-infrared region using an aperiodically poled lithium niobate waveguide.To investigate the coherence property of the high-order harmonic generation,DCS was performed at every generated spectral region from 450 to 3600 nm.The measured dual-comb spectra with distinctive tooth-resolved structures show the well-preserved coherence without apparent degradation after the cascaded quadratic nonlinear processes.The subsequent methane absorption spectroscopy at multiple spectral regions of different harmonics was carried out to characterize the spectroscopic capability of the system.These results demonstrate the potential of our scheme to generate compact and coherent broadband optical frequency combs for simultaneous multi-target detections. | YUANFENG DI ZHONG ZUO DAOWANG PENG DAPING LUO CHENGLIN GU WENXUE LI | 2023 | Photonics Research2023，11，8： | 0 |
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