The Generation And Application Of New Optical-optical Modulated Dual-comb Spectroscopy

Dual-comb spectroscopy(DCS),compared to the traditional spectral measurement techniques,is a revolutionary precise spectral measurement technique with the capacities of high frequency accuracy,high spectral resolution and rapid measurement speed.Thus,it is of great significance in many fields,such as the combustion diagnosis,environmental monitoring,and biomedicine.Today,the key of restricting the pratical development of DCS is to achieve the highly coherent and stabilitity dual-comb sources.However,traditional DCS demand to adopt bulk sophisticated control systems and operate in a well-maintained labortary environment,which prevents their widespread use in field applications.Passive coherent DCS has become one of the trends of the development of DCS for its inherent frequency stability,which avoids the locking process of the carrier envelop phase(CEP)and can maintain well stability.The traditional schemes for the generation of passive coherent DCS have many limitations on the optical characteristics including the spectral bandwidth,the operating wavelength,and the stability.In this thesis,the concept of optical-optical modulated OFC(OMFC)is firstly proposed.The near-infrared and mid-infrared DCS are achieved and then developed to achieve the precise spectral measurement of multiple molecules.Based on the mid-infrared system,the integrated design is performed to achieve the mobile dual-comb spectrometer.After that,the measurement of combustion exhaust in a non-laboratory environment is performed to analyze the component and concentration.These results promote the DCS into the future particle applications in the outdoor environment.The details and innovations are summarized as follows:1.The concept of OMFC is proposed.Based on the phase characteristics of optical parametric amplification(OPA)process,the concept of OMFC is presented.The generation of broad OMFC is achieved by the nonlinear modulation and power amplification of a narrow linewidth continuous-wave(CW)laser.Considering the theoretical study of DCS,the basic architecture and scheme of optical-optical modulated DCS are established.2.The near-infrared optical-optical modulated dual-comb spectrometer is obtained and the absorption lines of many molecules are precisely measured.Based on the concept of OMFC,the studies on the mature near-infrared DCS are carried out firstly.The 1550nm OMFC system consists of a home-made low-noise high-power Yb-doped fiber laser as the pump source,a commercial narrow-linewidth CW diode centered at 1550nm as the signal,and an ultrafast optical-optical modulator using periodically polarized lithium niobite crystals as the nonlinear media.Thus,the highly coherent near-infrared DCS is obtained.The coherent time reach up to 100 s and the relative linewidth of radio-frequency comb teeth is merely about 10 mHz,indicating the responding optical frequency resolution of 3.3 kHz.The scheme avoids the active control of the CEP and can achieve the long-term operation with 24 h.The absorption intensity and phase spectrum of many gases are measured.These results agree well with that from the HITRAN database with a resolution of 108 MHz and a measurement speed of ms level,which effectively indicates the ability of the dual-comb spectrometer for the precise spectral measurement.3.The mid-infrared optical-optical modulated dual-comb spectrometer is obtained and then the test of the combustion chamber exhaust is carried out.Based on the concept of the OMFC,the time and frequency evolution of the generation of mid-infrared OMFC is theoretically analyzed,which demonstrates the potential to achieve the generation of high-repetition rate ultrashort mid-infrared pulses.In the end,the mid-infrared pulses with a nearly Flourier transform-limited pulse duration of 84 fs(7.3 cycles)and a repetition rate of 160 MHz are obtained at a pump energy of nJ level in the experiment.These results show a well agreement with the numerical simulations.Besides,the scheme can achieve well spectral tunability.The direct output spectral range can reach up to server hundred nanometer and the average power is over several hundred milliwatt.After that,the mid-infrared optical-optical dual-comb spectrometer is established to achieve the parallel measurement of the absorption lines of multiple gases,including C2H2,CH4,H2CO,H2S,COS and H2O.Furthermore,the intergrated design of the mid-infrared DCS is carried out to obtain a mobile dual-comb spectrometer.Based on the system,the measurement of combustion exhaust in a noisy environment is peformed to analyze their component and concentration,which demonstrates the capability of achieving stable operation with the outstanding performance of the mobile dual-comb spectrometer.4.A octave-spaning mid-infrared OFC source is achieved.Based on the theory of mid-infrared coherent synthesis technique,the mid-infrared source with a pulse duration of 105 fs(8.5 cycles)and a spectral coverage spanning 3.4 to 4.2 ?m is obtained,which demonstrates the potential to achieve the broadband mid-infrared OMFC based on the coherent synthesis of multiple branches.On the other hand,the optimization of mid-infrared OMFC is performed based on the cascade parametric process and supercontinuum technique.In the end,a mid-infrared source with an octave spectral range from 1.8 to 4.2 ?m is obtained,which covers the absorption spectral range of multiple gases.