Research On The Novel Femtosecond Ti: Sapphire Regenerative Amplifier And Ultraviolet Frequency Conversion

The amplification and frequency conversion of femtosecond laser pulses are two vital parts in the development and application of ultrafast laser technology,which have important application value in the fields of physical chemistry,biomedicine,and ultra-precision micro-machining.In recent years,based on the developing of the peak power of the ultrafast and ultra-intense laser,they become the basic tools and means of many frontier scientific researches.Carrying out the research and design on the femtosecond laser pulses amplifier with excellent performance to extend its function and enhance the output parameters has many important realistic significances to promote the practical developing of the femtosecond amplification laser instruments and the application on the frontier domains.In this dissertations,a series of work focused on the femtosecond laser pulses amplification have been done.Meanwhile,in order to extend the covered wavelength bandwidth of the ultrafast laser to satisfy the needs of different application,a new nonlinear optical crystal K₃B₆O₁₀Cl?KBOC?was used to study the ultraviolet nonlinear frequency conversion.The main research works and the innovation results are summarized as follows:1.Based on the systematical introduction of the main components of the chirped pulseamplification?CPA?system including the laser oscillator,stretcher,amplifier andcompressor,first of all,the dispersion of the common transmissive materials areanalyzed and calculated in detail.By using the ray-tracing method,the dispersionsarisen from the Martinez stretcher and the grating pair compressor are also analyzed.The analytical expression of dispersion is derived and the simulation is also carried out.At last,based on the dispersion vector graph,the global optimization scheme of theoverall system dispersion is proposed and the algorithms are designed,which providea theoretical basis for the dispersion compensation in the CPA system.2.The research on the novel femtosecond Ti:sapphire regenerative amplifier with highrepetition rate of 1 kHz has been developed.The design and experiment of a novelthermal insensitivity cavity Ti:sapphire femtosecond regenerative amplifier arepresented.The experimental results are not only in good agreement with the theory,but also prove that the regenerative cavity has good thermal insensitivity.With thepump power of 20 W,the highest output amplification power of 6.5 W is achievedcorresponding to the efficiency of 32.5%.After the grating pair compressor,themeasured pulse duration is about 35 fs.3.We present a research on the novel multi-pass pumped femtosecond regenerativeamplifier based on Ti:sapphire thin disk.Firstly,the heat sink structure of coppertungsten alloy and the welding method of Ti:sapphire thin disk are designed.Inaddition,the temperature distribution of the crystal and the strain of the heat sinkresulting from the stress imposed by the variable velocity of water flow are analyzedand simulated.Then,under the pump power of 7.1 W and repetition rate of 1 kHz,theamplified output power of 1.21 W is achieved with 6 pass pump corresponding to aamplification efficiency of 17%by using a 2 mm long Ti:sapphire welded on theoxygen-free copper.The full width half maximum of the output spectrum width isabout 26 nm and the pulse width is about 38.3 fs.The beam quality M² is about 1.1.The experimental results show that the using of the Ti:sapphire thin disk as the gainmedium can not only ensure the efficient operation of the regenerative amplification,but also can effectively reduce the effect of the beam quality resulted from the thermaleffect of Ti:sapphire during the laser amplification process as well as the complexityof the system.4.Ultraviolet frequency conversion of ultra-short pulse in the novel nonlinear opticalcrystal K₃B₆O₁₀Cl has been researched for the first time.Employing a femtosecond Ti:sapphire amplifier at 1 kHz with pulse width of 27 fs and pulse energy of 0.8 mJ as thefundamental frequency source,ultraviolet?UV?pulse at 396 nm with maximum outputpower of about 220 m W and the highest efficiency of 39.3%are obtained in a1-mm-long KBOC.The ultraviolet pulse width of 83 fs is measured by adispersion-free transient-grating frequency-resolved optical gating.5.The thermal insensitivity Ti:sapphire femtosecond regenerative amplifier is adoptedfor the second harmonic generation and third harmonic generation.The deepultraviolet?DUV?pulse at 263 nm is obtained for the first time through two-stagefrequency conversion by using two KBOC crystals which length are 0.5 mm and 1 mm,respectively.The maximum output power of 5.9 mW and a conversion efficiency of4.5%versus the second harmonic power are achieved.The experiment results and theexcellent properties of KBOC crystal such as none hygroscopicity,high damagethreshold and wide transmission spectrum demonstrate that the KBOC crystal has agood application prospect in obtaining high power,DUV and ultra-short pulses.