Investigation Of High Repetition Rate Ytterbium-doped Dual Repetition-rate Mode-locked Laser System

In the past decade,dual-comb heterodyne technology as an emerging technique has demonstrated theoretically and experimentally that possesses preferable advantages of extremely precise spectral resolution,high sensitivity,static heterodyne detection and fast data acquisition speed and becomes a versatile tool for various applications such as dual comb spectroscopy(DCS),dual-comb absolute distance measurement(DCDM),3D-shape imaging,high speed asynchronous optical sampling and real-time trace gas detection.For these demanding practical applications,the dual-comb systems will benefit from ultrafast oscillators with high repetition rate,high average power,mutual-coherent phase and compact structure.However,dual-combs are still face many challenges in practical applications.One is that most of dual-comb systems still established with a pair of optical frequency combs that built independently with slightly detuned comb spacing.Introducing inevitably two complex feedback electronics circuits and cause the whole system of bulky,fragile,expensive and difficult maintenance.It is difficult to operate robustly in the external environment.The other is that the repetition rate of fiber-based dual-comb systems are relative low,which is generally tens to hundreds of MHz,limiting the measurement speed and sensitivity.It is imperative to develop practical,compact,high repetitionrate dual-comb devices.Dual repetition-rate ultrafast lasers generating asynchronous and mutual-coherent ultrafast pulses directly from a single cavity can be a promising alternative to the current dual-laser-based comb source.A dual-comb setup based on single laser has the advantages of compact structure,low cost and intrinsic mutual coherence.This technique paves the way for developing the compact,robust and environmental-immune dual-comb systems.In addition,semiconductor saturable absorption mirror(SESAM)mode-locked ytterbiumdoped solid-atate lasers have always been the focus of the development of high repetition rate optical frequency comb due to compact size,high repetition rate and low noise level.So developing high repetition-rate ytterbiumdoped dual-comb SESAM mode locked laser is an important way to achieve the compact,high repetitionfrequency dual-comb source.This thesis focuses on the subject of "high repetition-rate Yb-doped dual-repetition-rate mode locking laser system".Selecting a series of Yb-doped laser materials including Yb:YAG and Yb:Lu AG transparent ceramics fabricated by non-aqueous tape casting method and YAG/Yb:YAG/YAG planar waveguides(PWGs)grown by solid-state crystal growth method as the gain media.And making the best of semiconductor saturable absorption mirror(SESAM)mode-locked technology.Highly efficient continuous wave(CW)and wavelength tuning laser oscillators,single-repetition-rate mode-locked oscillators and a 1-GHz dual-repetition-rate mode-locked Yb:YAG ceramic oscillator are demonstrated successively.The main research contents are summarized as follows:1.A series of highly efficient Yb-doped CW oscillators are realized,in which Yb:YAG,Yb:Lu AG transparent ceramics and Yb:YAG polycrystalline PWGs are used as gain media successively.As a result,the high output power and high efficiency Yb:YAG transparent ceramic oscillator is realized based on the V-shaped cavity with a highest output power of 7.59 W and corresponding slope efficiency up to 84.4%.A highly efficiency CW Yb:YAG PWG laser with a highest output power of 3.4 W and slope efficiency of 60% in V-shaped cavity is realized.So far this is the best result of Ybdoped PWG laser grown by solid-state crystal growth method in the world.2.A series of novel Yb-doped wavelength tuning laser oscillators are developed by different dispersion prisms as tuning elements.The gain media used in the study of wavelength tuning lasers are the same as those mentioned in CW lasers,and the wavelength tuning properties of them in V-shaped cavity are investigated.As a result,a smooth continuous tuning band from 1012 nm to 1070 nm continuous tuning Yb:YAG ceramic laser is developed with the use of a SF 57.In Yb:AYG PWG laser,an optimum smooth tunable curve from 1021 nm to 1055 nm by inserting an intra-cavity SF57 prism.These results indicate that novel Yb-doped gain media have the potential to develop mode-locked lasers.3.A series of stable high repetition rate ytterbium doped single-mode-locked laser systems have been developed,which provide the key technical support for the development of high repetition-rate Ybdoped dual-repetition-rate mode locked laser.In the study,Yb:YAG,Yb:Lu AG transparent ceramics fabricated by non-aqueous tape casting method and Yb:YAG polycrystalline PWGs grown by solidstate crystal growth method are used as gain media successively.Through the use of a SESAM,A 102.8 MHz Yb:YAG mode-locked laser,a 101.7 MHz Yb:Lu AG mode locked laser and a 100 MHz Yb:YAG PWG laser have been implemented.The Yb:YAG PWG mode-locked laser grown by solidstate crystal growth method,to the best of our knowledge,is realized for the first time.These modelocked lasers possess similar characteristics of narrow spectral width,self-starting and stable operation.4.A high repetition-rate Yb:YAG ceramic dual-repetition-rate mode-locked laser is developed.Making a contrast that the previous research results of single-repetition-rate mode locked lasers,the Yb:YAG transparent ceramic is selected as the gain medium.In the experiment,the dual pulse gain competition and Q-switch instability are effectively suppressed by simplifying the cavity structure as a Z-shaped cavity and redesigning a dual-path end pump configuration.Finally,a 1-GHz pulse repetition rate Yb:YAG ceramic dual-repetition-rate mode locked laser is successfully developed.This is the highest repetition rate of the non-aqueous tape casting Yb:YAG ceramics.As a result,the dual-repetition-rate pulse trains have a detuned repetition-rate difference of 23 k Hz,the standard deviations of the repetition frequency and the difference are 1 k Hz and 183 Hz,respectively.The spectral half height widths are 0.65 nm and 0.73 nm,both spectra are similar,and the center wavelengths are fully overlapped,in addition,the dual-repetition-rate pulses have nearly same noise performance.This laser system provides an alternative solution for integrated real-time dual-comb precision metrology applications.