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Stimulated Raman Scattering Based On Gas-Filled Hollow-Core Photonic Crystal Fiber

Posted on:2010-06-14Degree:DoctorType:Dissertation
Country:ChinaCandidate:Q SunFull Text:PDF
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Hollow-core photonic crystal fiber(HC-PCF) can be used for enhancing the nonlinear interaction between the guided light and the hydro-medium filled in it,in particular,the gases.It has been shown that the threshold pump power of stimulated Raman scattering(SRS) with gas-filled HC-PCF may be greatly reduced.This implies that the gas SRS effect based on such a HC-PCF technique may find applications in nonlinear optics,laser technology and spectroscopy,and high-resolution trace gas detection,when rare earth doped fiber lasers are used as the pump.In this dissertation,the technical issues for the SRS effect based on gas-filled HC-PCF,including all-fiber high-pressure gas cell based on the HC-PCF,the SRS pump sources,and the demonstration of the SRS effect of hydrogen-filled HC-PCF, are studied in details.The main research works are as follows.The gain coefficient of stable state SRS is deduced form the classical electromagnetic field theory and the gain decline caused by the transient process is analysed.The different influences of pump linewidth on forward and backward SRS process are discussed.Furthermore,the theoretical model of SRS in HC-PCF is established,and the influences of transmittion loss and mode characteristic on SRS process are opened out.Finally,the mode characteristic of HC-PCF is analysed using the plane wave expansion method and the mode filed distribution is tested experimentally.Based on gas filling and leaking experiments,combined with the micro-pipe flow theory,the gas-filling and leaking characteristics for HC-PCF are studied.The results show that,the gas-filling speed of the HC-PCF is very slow,and a very long time is needed to build pressure equilibrium between the inlet and the outlet of the HC-PCF.The time required for building the pressure equilibrium in the HC-PCF may be efficiently shortened by reducing the volume of the outlet cavity.The HC-PCF has been successfully spliced to the standard single-mode fibers with low splicing losses by just using a normal commercial fiber splicing machine with the splicing parameters suitably optimized.Moreover,a new method to build all-fiber high-pressure gas cell based on the HC-PCF is present,and such an all-fiber high-pressure gas cell is also made with its final equilibrious gas pressure valued by the measured leaking speed evolution behavior. A passively mode-locked ytterbium-doped fiber laser(YDFL) is prepared with the nonlinear polarization rotation mechanism.By broadening the pulse duration with the pulse stacking technique based on a fiber ring,narrowing the pulse linewidth with a filter,and enhancing the pulse peak power with cascaded YDF amplifiers,a pulse train with repetition of 11.68MHz,3dB linewidth of 0.5nm,duration of about 800ps and peak power of 11.8W is obtained when the mode-locked YDFL is used as the seed source.On the other hand,the experimental investigations of the output characteristics for actively Q-switched fiber lasers with different configurations show that,the amplified stimulated emissions(ASEs) affect the generation process of the Q-switched laser pulses.Since the broadband ASE depletes most of the inversion population,it may be an adverse effect for the formation of the Q-switched laser pulses for either ring or linear cavity fiber lasers.When the ASE is suppressed with a narrow filter inserted in the cavity,the photon number may be limited at a low level right after the Q-switch is opened,which results in the gain much higher than the cavity loss at that time,and thus,benefitting the formation of the high-power Q-switched pulses.Moreover,the experimental results show that the Q-switched fiber lasers with linear cavity may be better than that with ring cavity because the former uses double-pass gain of the doped fiber.Based on the experimental results,a wavelength-tunable Q-switched YDFL with linear cavity is designed and built,and the pulse train with repetition of 5 kHz,duration of 30ns,peak power of 85W,and wavelength tuning range between 1060 and 1069nm is obtained finally.With the all-fiber high-pressure gas cell based on the HC-PCF described above, the SRS phenomenon for hydrogen gas,for the first time to our best knowledge,has been observed with such a Q-swithced ytterbium-doped single mode fiber laser as the pump source.For the compatibility of the pump laser with the single mode fibers, such SRS effects may be complemented with all-fiber structure,and thus may be useful for developing compact Raman devices,for instance,such as gas Raman lasers.The investigation results described above may be very helpful in developing gas Raman laser devices for satisfying the application requirements of new spectral region.
Keywords/Search Tags:hollow-core photonic crystal fiber (HC-PCF), stimulated Raman scattering (SRS), photonic bandgap (PBG), all-fiber high-pressure gas cell, passively mode-locking, Q-switching, fiber laser, amplified stimulated emission (ASE)
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