Characteristics Of Pulsed Lasers Based On Nd Doped Germanate Crystals And New Saturable Absorbers

Laser-diode?LD?pumped lasers have extensive applications in several fields,including communications,military weapons,and medical treatments.The advantages of diode-pumped lasers are compact structure,short pulse width,high peak power,and high beam quality.In recent years,all-solid-state lasers based on artificial crystals have developed rapidly to applications,and crystals are an important part of these lasers.These also promote the continuous exploration of new laser devices,to achieve better performance of all-solid-state lasers.The Nd³⁺ doped BGO and BGSO have the potential to become solid-state laser materials due to their high light output,high density,high energy resolution,and high radiation hardness.The crystal structure,luminescence properties,energy transfer,and interaction with lattice of Nd:BGO and Nd:BGSO crystals are studied by theoretical and experimental methods.And the laser characteristics of these crystals were comprehensively measured.The passively Q-switched operation was achieved by using new types of saturable absorbers?SAs?,and the thermal efficiency of crystals was reduced.The Nd:BGO and Nd:BGSO crystals have the potential to obtain compact and efficient small all-solid pulsed laser.In addition,these results also provide a reference for the optimum growth of this kind of crystal.The main content of this dissertation includes:1.The Q-switched principle and the mode-locked principle to generate the pulsed laser were illustrated.We introduced the development and properties of Nd:BGO and Nd:BGSO crystals.And the structure and characteristics of the new saturable absorbers—Bismuth nanosheets?Bi-NSs?and Indium Tin Oxide nanowire arrays?ITO-NWAs?were also described.2.The Nd:BGO crystal was successfully grown by the micro-pulling-down method,and first obtained the continuous-wave and pulsed laser operation with 880 nm LD pumping.In theory,we demonstrated the possibility of a 880 nm LD pumped Nd:BGO laser by the analysis of energy levels and spectral properties.The principle of reducing the thermal efficiency and the thermal loading by 880 nm LD pumping was expounded.And we also verified experimentally by using pumping sources with 808 and 880 nm in Nd:BGO crystal.In addition,based on Cr⁴⁺:YAG SA,the Q-switched Nd:BGO laser performance under different pump wavelength conditions was compared.Compared with the pump wavelength of 808 nm,the 880 nm LD directly-pumped Nd:BGO laser has the potential to obtain high efficiency,high beam quality,and high repetition rate.3.The Bi-NSs were prepared by the sonication method and the nonlinear optical properties of this material were characterized.The saturation fluence and the modulation depth of the Bi-NSs SA were characterized using a Z-scan method at 1 ?m.The Bi-NSs were employed as SAs to generate a passively Q-switched Nd:BGO laser for the first time.4.The structure and optical spectra characteristics of the Nd:BGSO crystals were observed.We first demonstrated a diode-pumped continuous-wave and passively Q-switched Nd:BGSO laser.The continuous-wave Nd:BGSO laser performance under different pump wavelengths of 808 and 880 nm was compared.On the basis of adjusting the continuous-wave laser to the optimum state,the Bi-NSs SA was inserted into the resonator to realize the passively Q-switched operation.Compared with the Nd:BGO laser under the same experimental conditions,the results revealed the potential of Nd:BGSO crystals as the laser gain medium.5.By using a SESAM,the LD pumped passively Q-switched mode-locked Nd:BGSO laser was demonstrated.The ultrashort pulsed Nd:BGSO laser was realized under 880 nm pumping.At the maximum absorbed pump power,a maximum Q-switched output power was 0.176 W,a shortest pulse width was 1.531 ns,and the corresponding repetition rate was 54.35 MHz.6.ITO-NWAs SA was fabricated in this study using a CVD method,and the broadband saturable absorption properties of the sample were first investigated in all-solid-state lasers.The saturable absorption properties of ITO-NWAs SA were characterized in the near-infrared region,and the saturable intensities and the modulation depths of this material were obtained at different wavelengths.We demonstrated passively Q-switched all-solid-state lasers by using ITO-NWAs as the SA and confirmed the potential of ITO-NWAs as broadband SA materials.In addition,the passively Q-switched laser operation of Nd:BGSO crystals was demonstrated based on ITO-NWAs SA.The results indicate that ITO-NWAs,exhibiting high chemical stability,high damage threshold,large optical nonlinearity,and broad range of saturable absorption spectrums,can be utilized as a promising effective optical modulator for ultrafast photonics.