Theoretical And Experimental Investigation Of Full-Spectrum White Light Femtosecond Laser

The ideal high-performance white laser with superior performance such as very large bandwidth,high-peak power,high pulse energy,and high spatial-temporal coherence is a brand-new laser that has important application prospects in all fields of modern science.Over the past60 years,the organic combination of laser technology and nonlinear optics has effectively driven the broadening of the laser spectrum range to a high level.However,the direct generation of high-brightness ultraviolet（UV）-visible（Vis）-infrared（IR）（UV-Vis-IR）full-spectrum white light femtosecond laser sources is still an ambitious challenge and a great goal.The work in this thesis is focused on the generation and application of full-spectrum white light femtosecond laser,mainly including the development of extremely broadband nonlinear optical calculation methods,the design and fabrication of extremely broadband nonlinear photonic crystal materials,the development of UV-Vis-IR full-spectrum white light femtosecond laser technology and its application to the single-shot femtosecond laser spectroscopy,and other research.The main innovative achievements are as follows:1.A complete set of broadband nonlinear coupled-wave theory has been established to describe the spatial-temporal evolution behavior of ultrashort laser pulses in nonlinear crystals.This method can qualitatively and quantitatively explore and visualize the nonlinear optical interactions of ultrashort laser pulses in nonlinear materials,and provide accurate theoretical support and guidance for experimental studies.2.The comprehensive performance of the white light femtosecond laser is continuously enhanced via synergic second-order nonlinearity(2^nd-NL)and third-order nonlinearity(3^rd-NL).Based on an efficient synergic 2^nd-NL and 3^rd-NL ultra-broadband second harmonic generation scheme,using a Ti:sapphire femtosecond laser with 3 m J pulse energy to pump the cascaded optical module composed of fused silicon and ultra-broadband white light nonlinear crystal,we successfully realize the generation of ultra-flat,ultra-broadband white femtosecond laser with m J magnitude pulse energy and 3 d B bandwidth covering 385-1080 nm.Based on the synergic2^nd-NL and 3^rd-NL high harmonic generation scheme,a single ultra-broadband white light nonlinear crystal pumped by a mid-infrared femtosecond laser with 45μJ pulse energy is used to successfully generate a 350-2500 nm UV-Vis-IR ultra-continuous white light femtosecond laser with a single pulse energy of 17μJ and a conversion efficiency of 37%.Based on the third-order self-phase modulation effect and the second-order nonlinear high harmonic generation scheme,an intense UV-Vis-IR full-spectrum femtosecond laser source（with 300-5000 nm 25 d B bandwidth）with 0.54 m J per pulse is successfully obtained,by sending a 3.9μm,3.3 m J mid-infrared pump pulse laser into a cascaded architecture of gas-filled hollow-core fiber（HCF）,a bare lithium niobate（LN）crystal plate,and a specially designed chirped periodically poled lithium niobate crystal（CPPLN）.3.Based on the developed high-performance ultra-broadband white light laser source,a single-shot femtosecond pulse laser spectrometer has been successfully developed.For the first time,the spectral range of the spectrometer has been extended from the ultraviolet to the near-infrared region（3 d B bandwidth covering 385-1080 nm）with ultra-high pulse energy（>1 m J level）and pulse duration in the order of 100 fs.Preliminary applications have been made for single-shot ultrafast measurements of atomic and molecular spectra.4.Discovery of novel physical phenomena:rainbow Cherenkov radiation and ultra-broadband Raman-Nath diffraction effects.It is found that rainbow Cherenkov radiation can be generated in a single periodically poled lithium niobate（PPLN）nonlinear crystal based on the ultra-broadband longitudinal phase-matching principle under the synergic mechanism of 2^nd-NL and 3^rd-NL.Multi-order ultra-broadband Raman-Nath second harmonic generation can be realized in the PPLN and chirped periodically poled lithium niobate（CPPLN）nonlinear crystal based on the ultra-broadband transverse phase matching principle.These novel phenomena reveal a wealth of new physics of nonlinear optical interactions,which will create better techniques and tools for applications such as ultrashort pulse characterization and nondestructive identification of domain structures.