Research On The High Repetition Frequency, High Power Laser System Used In XUV Optical Frequency "Combs" System

Femtosecond laser optical frequency "combs" have revolutionized the measurement of optical frequencies and ultrafast laser science.The frequency "combs" at ultraviolet(UV)and extreme ultraviolet(EUV)wavelengths open the door for frontier of precision spectroscopy and ultrafast science.Many premier measurement labs are engaging in the investigation of the UV & EUV optical frequency "combs".This dissertation gives the theoretical and experimental investigation on the high repetition frequency,high power laser system in 1μm region which used to generate UV & EUV optical frequency "combs".We succeeded in the experiments of compact diode-pumped femtosecond oscillators, high power double-clad fiber amplifier and accurate synchronization of remotely separate ultrashort lasers and original and some important results achieved.By using the integration of these key techniques,a high repetition frequency,high power laser system has been developed around 1μm by use of which as the source combined with OPCPA laser system,so that the frequency comb from the fundamental laser will also be usable in the UV & XUV.The main results have been summarized as following:1.We developed a series of key techniques related to compact diode-pumped ultrafast ultrashort oscillators in 1μm region:1)An efficient diode-pumped laser was realized based on a new ytterbium-doped laser crystal Yb:GSO,wherein Yb³⁺ions exhibit the largest ground-state splitting among all the ytterbium-doped crystals.A slope efficiency up to 86%and a pumping threshold as low as 127 mW were achieved for a continuous-wave Yb:GSO laser at 1092.5 nm under the pump of a high-brightness laser diode.2)A continuous and smooth tuning range broader than 97 nm,from 1009 to 1112 nm of Yb:Gd₂SiO₅ tunable laser was realized with an SF14 prism as the intracavity tuning element. 3)Experimental investigation on a new ytterbium-doped alloyed laser crystal,Yb:GYSO.High-power cw Yb:GYSO laser can be tuned around 1083 nm,which may serve as a favorable candidate for optical pumping of He³ and He⁴,providing wide potential applications in helium magnetometers.The maximum output power reached 7.5 W,the maximum lasing slope efficiency reached 79%.4)Efficient tunable simultaneous continuous-wave(cw)multi-wavelength diode-pumped Yb:GYSO laser are of interest for various practical applications such as nonlinear frequency mixing,fluorescence excitation and medical instrumentation.Under different cavity alignments,dual-, three-,four-wavelength lasers were successfully realized around 1041～1043,1048～1052,1056～1063,and 1080～1089 nm.5)In the continuous-wave laser operation of Yb:LuYSiO₅(Yb:LYSO),a maximal slope efficiency of 96%was achieved.By using a dispersive prism as the intracavity tuning element,we demonstrated that the continuous-wave Yb:LYSO laser exhibit a continuous tunability in the spectral range of 1014.4-1091.7 nm.6)Compact femtosecond laser operation of Yb:Gd₂SiO₅(Yb:GSO)crystal was demonstrated for the fisrst time,to our knowledge.A pair of SF10 prisms was inserted into the laser cavity to compensate for the group velocity dispersion.The mode-locked pulses centered at 1031 nm were compressed to 343 fs.2.Based on the ytterbium-doped double-clad fiber,we have developed a high power,high repetition rate amplification system.1)In cw double-clad fiber amplifier,the maximum output power reached 12 W,corresponding slope efficiency reached 57%.In femtosecond amplifier,the maximum output power reached 10 W,corresponding slope efficiency reached 72%.2)We experimentally demonstrated diode-pumped continuous-wave and tunable laser operation of yb³⁺-doped yttrium lanthanum oxide transparent ceramic(Yb:(Y_1-xLa_x)₂O₃,x=0.05)which was fabricated by low-temperature sintering.A maximum output power of 2.0 W and a smooth tunable curve from 1018 to 1086 nm were obtained.Compact picosecond laser operation was demonstrated for the fisrst time,to our knowledge.3.A novel designed scheme of accurate synchronization of signal and pump laser of OPCPA system to generate the UV & EUV optical frequency "combs".We experimentally demonstrate synchronization of a pulsed slave fiber laser based on nonlinear polarization rotation effect at 1550 nm with a remotely separate femtosecond master laser at 1030 nm with a large cavity mismatch length up to 14 mm,at least two orders of magnitude longer than those hitherto reported.