The Femtosecond Laser Properties Of Yb-doped LuAG?CLGA And CGA Crystals

The innovative development and application of ultrashort pulse laser is one of the important frontier fields in current international laser technology and even in modern science and technology.After the mature developments and wide applications of Ti:sapphire femtosecond lasers,due to the advantages such as small size,low cost,high efficiency and wide gain spectrum,diode directly pumped Yb-crystal based lasers gradually become the most promising substitute of Ti-sapphire lasers in 1.0 ?m.In this thesis,based on novel Yb:Lu3Al5O12(Yb:LuAG),Yb:CaLuxGd1-xAlO4(Yb:CLGA),and Yb:CaGdAlO4(Yb:CGA)crystals,the spectroscopy and ultrafast laser performances are systemically studied by using SESAM,2D materials,and the third-order nonlinear effect of the gain mediums.The main research contents and significant achivements are as follows:In chapter 1,the developments of femtosecond lasers especially the laser-diode-pumped Yb-crystal based femtosecond lasers are introduced in detail.Then the laser properties of different kinds of Yb-doped crystals are summarized thus the research content and significance of this paper are pointed out.In addition,the ultrsfast laser properties and the corresponding developments of the gain mediums and saturable absorbers used in this paper are introduces detailly.In chapter 2,the theories of Kerr-lens mode-locking are analyzed.For the nonnegligible dispersion in femtosecond lasers,the calculation methods of crystals and dispersion compensation methods are introduced detailly.Moreover,for the discrete peaks in the spectra of femtosecond lasers,two possible causes and the corresponding discrimination method are analyzed theoretically.In chapter 3,based on SESAM as saturable absorber,watt-level femtosecond pulses are obtained for the first time from the Yb:LuAG mode-locked laser.The average output power,pulse duration,and central wavelength are 1.07 W,760 fs,and 1032 nm,respectively.The results indicate Yb:LuAG is a promising gain medium for generating high-power femtosecond pulsed laser.Based on the popular 2D materials,we prepared high-quality black phosphorus(BP)saturable absorbed mirror and characterized it.Using BP as optical modulator in the cavity,a dual-wavelength synchronously mode-locked Yb:LuAG laser is achived for the first time.The result demonstrated the potentical of BP in multi-wavelength ultrafast lasers.In chapter 4,the spectroscopy,continuous-wave laser,and ultrafast properties of the novel disordered Yb:CLGA crystal with 1.4 at.%Yb consentration are investigated systematically.The complex and disordered lattice field results in its wide emission spectrum with a FWHM of 83 nm.Compared to the a-cut crystal,the c-cut crystal has a wider spectrum and higher gaim cross-section,which make it a promising gain medium generating high power and shorter pulses in ultrafst lasers.Based on a quartz birefringent filter,the wavelength-tunable continuous-wave Yb:CLGA laser is achived with a wavelength-tunable range of 1023.1 nm to 1088.8 nm.Based on SESAM,a passively mode-locked Yb:CLGA femtosecond laser is realized firstly,corresponding to the pulse duration of 517 fs and spectral width of 2.93 nm.By optimizing the laser cavity with increasing the laser density in the Yb:CLGA,the SESAM based Kerr-lens mode-locked Yb:CLGA laser is achived for the first time,corresponding to a pulse duration of 106 fs and spectral width of 12 nm.Further by optimizing the intracavity dispersion compensation,the spectrum broadens to 18.5 nm and pulse shortens to 69.6 fs,corresponding to the outpout power of 232 mW and central wavelength of 1054 nm.The results indicate that Yb:CLGA is an excellent gain medium for generating Sub-100 fs pulsed laser.In addition,by using BP as saturable absorber in Yb:CLGA laser,a femtosecond solid state lasers based on BP as saturable absorber is realized for the first time.The average output power and pulse duration are 820 mW and 272 fs,respectively.The results demonstrated BP is a promising optical modulator in high-power femtosecond solid state ultrafast lasers.In chapter 5,the 4.8 at.%Yb:CLGA cryatal is grown and the corresponding spectroscopy,optical nonlinearity and continuous-wave laser properties are sdutied compared to 1.4 at.%Yb:CLGA.With higher Yb doping concentration,the spectrum is obviously broadened,while the nonlinear refraction index is changeless,which indicate the higher Yb-doped Yb:CLGA has potential to generating shorter pulses.Considering the low crystal quality of 4.8 at.%Yb:CLGA,we finally choose 5 at.%Yb:CGA with comparable spectrum and investigated its ultrafast laser properties.By optimizing the intracavity dispersion compensation,pulses as short as 51 fs are realized with the output power of 220 mW and spectral width of 23.57 nm.Additionally;the band structure and saturable absorption of 2D ReS2 are investigated.Based on first principle theory,the relationship between defects and band steucture is calculated and analyzed.The results indicate that the bandgap of ReS2 reduces with the increase of S vacancies.In experiment,we prepared ReS2 saturable absorber and characterized it in detail.By using the ReS2 as satuable absorber in Yb:CGA laser,323 fs mode-locked pulses are obtained with output power of 350 mW.Both the theoretical analysis and experiments demonstrated that ReS2 is a potential optical modulator in ultrafast lasers.