Generation And Application Of Tunable Femtoseond Laser Pulse Synchronously Pumped By All Solid State Mode-locking Laser

High power,high repetition rate,widely tunable ultrafast lasers are applied in various fields of time-resolved spectroscopy,biological microscopy imaging,terahertz-wave?THz?generation and laser communication.Nonlinear optical frequency conversion technologies based on a Yb³⁺bulk material femtosecond laser system can generate new laser wavelength,which can not be produced directly from the traditional laser sources.Optical parametric oscillators?OPOs?is a continuously tunable wavelength laser source,whose wavelength covers from ultraviolet to mid-infrared.It is a feasible method that using all solid-state laser sources to pump OPO with intracavity or extracavity sum-frequency to generate high power widely tunable femtosecond pulse.This thesis focuses on the experimental research of femtosecond OPO pumped by all solid-state laser and high power directly pumped by laser diodes?LD?.In addition,we also study the two-photon fluorescence microscopy in biological microscopy imaging based on home-made widely tunable femtosecond OPO source.The main research works in this thesis are summarized as follows:1.We have simulated the dynamic process of femtosecond OPOs based on the three-wave interaction equation.We have studied the factors which effects on the frequency conversion efficiency and pulse duration of the output pulse,such as group velocity mismatch,group velocity dispersion and crystal length.Based on a commercial Yb:KGW all solid-state femtosecond laser source,we have generated high power widely tunable near-infrared to mid-infrared femtosecond pulse combined with KTA and KTP crystal.The signal wavelength is covered from 1.41-1.71?m,the corresponding idler wavelength is from 2.61-3.84?m.The OPO generates as much as2.32 W of signal power and 1.31 W of idler power,corresponding to a total conversion efficiency of 51.8%.By compensating intracavity dispersion,the signal pulse has a nearly Fourier transform-limited duration of 129 fs at 1.52?m.2.With a LBO crystal,the characteristics of second harmonic pulse from Yb:KGW laser source is studied.Based on this 515 nm femtosecond pump source and BIBO crystal,we have studied the properties of output pulse at different repetition rate of 75.5 MHz,151 MHz and 755 MHz.Operating at 75.5 MHz,the signal can be tuned from 693-1000 nm,the corresponding idler is covered from 1061-2005 nm.Ultraviolet femtosecond pulses from 350-488 nm has been obtained by extracavity second harmonic generation?SHG?in the OPO.3.A high-repetition-rate,tunable femtosecond dual-signal-wavelength OPO based on BiBO crystal has been demonstrated.We have studied the process of the signal dual-signal-wavelength in OPO.The phase-matching condition is not quite rigor pumped by high peak power lasers.Our results shows that the net-zero dispersion,does not only determine the dual-wavelength oscillation.The balance of phase-matching condition and group velocity mismatch between dual signals and pump source is more significant for generation of dual-signal.The dual-signal-wavelength is tunable from700 to 1000 nm at the repetition rate of 151 MHz.4.A femtosecond laser synchronously pumped self-starting Ti:sapphire oscillator has been investigated both experimentally and theoretically.Except for self-phase modulation,it is worth noting that the high-efficiency cross-phase modulation of Ti:sapphire pulses and pump pulses spread together with high third-order nonlinearity in the crystal can generate efficient temporal absorption even if there exists negative dispersion in the cavity.Wavelength shifts of the pulses induced by cross-phase modulation combine with the wavelength dependence of the cavity round-trip time for the efficient synchronization of the femtosecond pulse trains.The repetition rate of the Ti:sapphire laser is set to be 151 MHz,which is successfully locked to the twice that of the pump laser.Using the chirped mirrors and wedges to compensate the intracavity dispersion,the pulse duration is 12.7 fs and the output power is 256 mW.5.The high power passively mode-locked Yb:KGW and Yb:CGA oscillators has been demonstrated.We have simulated the structure of cavity and calculated the dispersion induced by the elements in the cavity.Using the fiber-coupled LD as pump source and with 28.4 W pump power,7.6 W mode-locked pulses are obtained from Yb:KGW oscillator,the corresponding pulse energy is 97 nJ and the peak power is0.606 MW.We also have obtained high power picosecond mode-locked pulses from Yb:CGA oscillator.The maximum output power is 10.3 W,and the corresponding pulse energy is 127 nJ.6.Using the home-made widely tunable femtosecond OPO as the laser source,we have studied the biological microscopy imaging.Firstly,the femtosecond OPO source has been designed and developed succefully.Then we collaborate with SIBET,CAS to study the two-photon fluorescence microscopy in biological microscopy imaging and has obtained satisfactory results empirically.This home-made femtosecond OPO provides a powerful driving source for two-photo fluorescence biological microscopy and establishes the foundation for the subsequent industrialization.