| Due to ultra-short pulse width,ultra-high repetition rate and ultra-wide spectral composition,ultrafast fiber lasers have been widely used in spectroscopy,optical communication,advanced manufacturing,precise measurement,medical imaging and other fields.As the application scenes become more and more instantaneous,the transient characteristics of ultrafast lasers,as tools for loading information,will hinder the extraction of transient information of measured objects.With the variation of time scale,the physical characteristics of ultrafast lasers will change accordingly.Especially,during the formation and regulation of ultrafast lasers,the evolution of optical parameters will destroy and reshape the equilibrium state of linear and nonlinear effects in the laser cavity,resulting in unexpected optical soliton behavior,limiting the regulation rate,and thus affecting the dynamic performance of many high-speed measurement and imaging systems.However,due to the limitation of the response speed of photoelectric instrument,the transient non-repeatable optical parameter evolution cannot be characterized by traditional time-frequency measurement methods.Therefore,this dissertation will focus on the parameters real-time measurement and soliton evolution laws of ultrafast lasers.While revealing rich transient dynamic processes to provide new insights into the underlying physical mechanisms of soliton lasers,this dissertation will further promote the application of ultrafast lasers in high-speed precise measurement and light-matter interactions in a shorter time scale.The specific research contents of this dissertation are as follows:(1)The passive mode-locking techniques and output pulse types of ultrafast fiber lasers are systematically summarized.The advantages and disadvantages of existing ultrafast laser control methods are analyzed.The research status of ultrafast laser dynamics is clarified.The shortcomings of real-time measurement techniques of laser parameters are discussed.The research route includes measurement technology,laser time-frequency parameter regulation means,soliton evolution laws.(2)Based on the generalized nonlinear Schr?dinger equation of pulse transmission in the fiber,combined with the basic structure of an ultrafast fiber laser,the dynamic theoretical model of passive mode-locked fiber laser is established.The influence of gain and dispersion on the time-frequency parameters during the soliton evolution process is simulated and analyzed,which provides theoretical support for subsequent laser construction,regulation and dynamics analysis.The realization principles of dispersive Fourier transform based real-time spectral measurement and time lens based temporal microscopy are deduced and simulated to provide guidance for the subsequent construction of time-frequency parameters real-time measurement techniques.(3)The transient spectra measurement technique of controllable devices assisted by dissipative soliton light source is proposed.Taking an acousto-optic grating as an example,during the processes of passband dynamic switching and sweeping,the response time of280 μs and sweeping speed of more than 13000 nm/s are visually characterized.The 8MHz spectral refresh frame rate of the system is verified.It can provide measurement technique for dynamic performance characterization of optical components of controllable laser systems.(4)An all-optical self-synchronized time lens based on self-frequency shift of Raman solitons is proposed.Combined with the dispersion Fourier transform technique,a real-time measurement system for characterizing time-frequency parameters of ultrafast laser is constructed to achieve the time-frequency resolution of 160 fs,0.05 nm,and the temporal magnification of 301 times.The measurement system can synchronously magnify the ultra-short pulses at any repetition rate without limited by the length of the under-test pulse train.It can provide measurement technique for dynamic parameters characterization of ultrafast lasers.(5)Based on the real-time measurement technique of time-frequency parameters,in the anomalous dispersion region,two new routes of traditional soliton formation are revealed,which includes the generation and evolution of shaking soliton molecular triplet and the generation and annihilation of multiple pulses.In addition,in the normal dispersion region,a new route of dissipative soliton formation with mutual-ignition asynchronous-excitation transient solitons is revealed.(6)The optically and acoustically controlled ultrafast fiber lasers with adjustable parameters are proposed and constructed.The wavelength and pulse width are linearly tuned with sensitivity of 2.9 pm/m W and 470 fs/m W.The wavelength tuning range greater than 30 nm with response time less than 200 μs is realized.Furthermore,based on the real-time measurement technique of time-frequency parameters,it is demonstrated that the laser can perform continuous wavelength sweeping with speed greater than 10000nm/s while maintaining the mode-locked state.(7)Based on the real-time measurement technique of time-frequency parameters and the high-speed polarization analyzer,the energy coupling phenomenon during noise-like single-pulse switching to double-pulses is revealed.Meanwhile,the optical polarization rogue wave generated during the dissipative soliton explosion is revealed.In this dissertation,the transient dynamic phenomena of ultrafast lasers in multiple dimensions under the effect of nonlinear effects and control methods are investigated from the real-time measurement of ultrafast laser parameters to the law of optical soliton evolution.The real-time measurement techniques of optical devices and laser parameters can provide powerful tools for the dynamic characterization of ultrafast laser systems.Further exploration of the new evolution law of optical solitons can provide a new insight for the underlying physics of ultrafast lasers,and provide ultrashort pulse light sources with extremely controllable temporal and frequency parameters for high-speed precise measurement system. |
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