| Connecting optical and microwave frequencies,optical frequency comb（OFC）is promising for optical clock,spectral measurement,frequency synthesis and many other fields.In particular,high fundamental repetition rate（FRR）OFC plays an important role in astronomical spectrometer calibration,high-quality nonlinear optical microscopy imaging,and optical arbitrary waveform generation.So far,OFCs at 1.0μm and 1.5μm have been intensitvely inesitigated and commercially available.The OFC at 2.0μm,however,is still under study.The study of high FRR OFC at 2.0μm,especially,has largely been limited by the length of Tm3+doped fiber（TDF）.In this thesis,mode-locked fiber lasers at 2.0μm with different FRRs are investigated.Starting from 2.0-μm mode-locked fiber lasers with low FRRs,a high FRR ultrafast fiber laser at 2.0μm is achieved at a FRR of up to GHz.Then,an all-fiber optical amplifier system is explored for power scaling of high FRR femtosecond pulses,based on which the generation of supercontinuum is studied.After locking the repetition rate of the 3 GHz fiber laser,a dynamic high FRR optical comb system is implemented.Finally,the high FRR comb is further employed to construct the dual-comb spectroscopy.The results are detailed as follows:（1）Three kinds of all-fiber mode-locked lasers at 2.0μm are studied,including Q-switched mode-locking with rectangular noise-liked pulse burst,non-reciprocal phase shifting in nonlinear optical loop mirror（NOLM）,and nonlinear phase shift in semiconductor saturable absorber mirror（SESAM）.The high FRR femtosecond pulses at 2.0μm are obtained.（2）A nonlinear chirped pulse amplifier system with a saturated power of watt is studied for the power scaling of high FRR femtosecond pulses.Firstly,the pulses from the seed laser are chirped（broadened）by a piece of passive fiber with normal dispersion.Then,the chirped pulses are compressed by nonlinear effects from another piece of nonlinear fiber.The high energy output pulses exhibit a pulse duration of 126 fs and an average power of 8 W.（3）Repetition rate locking of the high FRR temtosecond pulses is studied.By regulating the temperature of the mode-locked cavity,the stabilization of the repetition rate of the mode-locked pulses is achieved.Then,the real-time photoelectric feedback method is used to instantly adjust the repetition rate of the mode-locked laser,such that the repetition rate of the mode-locked laser can keep consistent with the reference frequency.（4）A 2.0-μm dual-comb system with 3 GHz FRR is investigated.The system can measure the absorption spectrum of the gas sample in single shot.The detectable spectral range is 1917 nm～1937 nm,and the detection spectral resolution is about 14.1 pm.In order to verify the feasibility of the high FRR dual-comb spectroscopy,1%ammonia is tested in real time. |
