The Generation Of High Efficient Raman Sidebands

The technology of ultra-short pulse has been developing increasingly in recent decades,which has been applied in variety of fields.The researchers exploit them as optical source discovering the technology of time-resolved spectroscopy and pump detection such as Time-resolved fluorescence spectroscopy,differential absorption spectroscopy,reflectance spectroscopy.Several generation methods of ultra-pulse have been presented,which are high harmonic method,and stimulated Raman scattering method.By phase-locked lasers with frequencies of 2f and 3f,phase-frequency components of f-6f are generated in the nonlinear crystal through nonlinear processes such as frequency multiplication and difference frequency,and then frequency spectrum is synthesized to generate sub-femtosecond pulses.This is the use of spectrum synthesis.According to the generation of higher harmonics in the semiclassical theory,there are three processes.The first process is under the action of the external field.The electrons break free from the bondage of atoms or molecules and become free electrons.The second process is free electrons.Accelerating movement in the external field,and the direction of the light field,back to the original parent,the final process is,in the complex process with the mother,the light field radiation higher harmonics,then use the metal membrane filter filter Some subharmonic components in the cut-off region can provide sub-femtosecond pulse output.This method is the higher harmonic method.The popular method is utilizing the excited para-hydrogen to produce a Raman scattering discrete spectrum,resulting in a broader Raman sideband spectrum so that ultra-short pulses are generated by compressing the spectrum.The purpose of the study was to produce efficient Raman sideband light.Raise the energy of high-order Raman sidebands,and make the Raman sideband light form continuous.We optimized the density of the para-hydrogen molecules as the medium and optimized the interaction length of the pump light with the medium to produce high-efficiency higher-order Raman scattering spectra.The most important work in this thesis is that excited para-hydrogen was used to generate Raman scattering discrete spectra,and Raman sideband light was optimized.We mainly introduce the background,applications and researching aim of the ultra-short pulse.Moreover,we summarized the history of the development of ultra-short pulses,and the current methods of generating mainly ultra-short pulses.At last,the composition of this paper is described.The basic theory of generated ultra-short pulse is demonstrated.Basing on the quasi-three-level system,the theory of the conditions that produce Raman sidebands whose propagation in the medium was analyzed.Moreover,an efficient method that modulates small-signal coherent light is proposed.Aiming at the problems encountered in the second harmonic generation of nonlinear crystals,the methods of quasi-phase modulation and refractive index matching are proposed,which is efficiently capable of avoiding the adverse effect that is the birefringence of the crystal itself.The generation equipment of optical source and theory are introduced.Using a 801nm continuous beam,a 532nm pulsed light source was used to generate an ?0 pulsed light source with a pulse wavelength of 800nm.The mass of the pulse of ?0 was measured with a beam quality analyzer.It was proved that the quality of the beam was entirely capable of producing Raman sideband light.Then we introduced the construction of an optical parametric amplifier and used an optical parametric amplifier and a beam of ?0 to pump ?-1 to increase the beam intensity of ?-1 to change the continuous light ?-1 to pulsed light.The final measured wavelength of the 2.1 beam was 1200 nm and the beam quality was measured using a beam quality analyzer.The measured result shows that the ?-1 beam can produce Raman sideband light completely.In addition,we obtained 800nm and 1200nm optical source whose quality has been tested by beam quality analyzer and the results show that the quality of those two optical sources are completely capable of generating Raman sidebands.Furthermore,the equipment of generating Raman sidebands was built,and the results of the experiment were theoretically analyzed.At last,KTP was exploited to optimize the new experimental system,the higher quality of exciting light were obtained.The energy of the double pump light was increased from ?0:5.5 mJ and ?-1:855 ?J to?6 mJ and?6 mJ,respectively.Through the past experiments we have discussed the factors that affect the frequency modulation.One is the line width of the Raman transition and the other is the number of molecules that interact with the light.Through the past experiments we have discussed the factors that affect the frequency modulation.One is the line width of the Raman transition and the other is the number of molecules that interact with the light.Moreover,we experimentally measured Raman line-width and optimized Raman line-width in two ways.One of the aspects is to optimize the Raman line-width from the molecular density.From the experiment,we obtain the optimal condition of 7.6×1019cm-3 as the para-hydrogen molecule.Another aspect is to optimize the Raman line-width from the molecular interaction length.When the lens combination reaching f= 250,400mm,we think that can produce the best interaction length and the length of each interaction are 2ZR(?-1)= 11.6cm,2ZR(?0)= 14.5cm.All in all,this thesis analyzes the last experiments to figure out the ways to optimize the Raman sideband spectrum.The broader Raman sidebands spectrum were obtained experimentally,from eight Raman sidebands obtained the previous experiments to ten Raman sideband lights,which could be the foundation for the laboratory aiming at the achievement of generated attosecond pulses.