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Research On Fiber Femtosecond Laser Self-Similar Amplification System

Posted on:2014-08-25Degree:DoctorType:Dissertation
Country:ChinaCandidate:S J WangFull Text:PDF
GTID:1228330422968107Subject:Optical Engineering
Abstract/Summary:PDF Full Text Request
Yb3+-doped fibers feature high pumping efficiency, broad emission bandwidth,and low thermal load, make them ideal gain medium for femtosecond laser.Self-similar amplification actively exploits the nonlinearity to output linearly-chirpedparabolic pulses, allowing for transform-limited pulses after compression. Yb3+-dopedfiber self-similar amplifiers are very attractive for generating high-average-powerhigh-energy high-peak-power femtosecond pulses, and promise their uniqueapplications in scientific research and industrial production. This thesis is dedicated toimprove the performance of Yb3+-doped fiber femtosecond laser self-similaramplification systems. Theoretical and experimental researches are mainly carried onself-similar amplification dynamics, chirped-pulse amplification technique andgain-shaping effect. The dissertation can be summarized as bellow:1. In the case of a long enough normal dispersion fiber amplifier, a linearly-chirped parabolic pulse asymptotic self-similar solution to the nonlinear Schr dingerequation with constant gain is found. The optimum initial pulse duration and pulseenergy that gives the fastest convergence to the parabolic pulse solution under certainamplifier parameters are developed.2. A numerical model of nonlinear amplification basing on the absorption andemission cross-sections of Yb3+-doped fiber is constructed. The influences of gainfiber length and initial pulse parameters, including the center wavelength, duration,chirp and temporal profile, to self-similar amplification under the disturbance ofgain-shaping effect are discussed for the first time.3. A nonlinear pulse pre-shaping self-similar amplifier is demonstrated for thefirst time. The pre-shaper consists of a pair of gratings and a segment of single modefiber, to optimize the initial pulses temporally and spectrally. With this optimization,self-similar amplification is realized in a2.2m-long Yb3+-doped fiber, generating60fs transform-limited pulses after compression. This nonlinear pre-shaping methodcould release the seed quality required for self-similar amplification, thus facilitate anall-fiber system.4. The impacts of initial pulse parameters including the sigh and magnitude ofchirp, and pulse energy on nonlinear amplification are discussed experimentally. Aspectral-breathing self-similar amplifier is demonstrated for the first time. Thespectral-breathing behavior of negatively-chirped pulses during amplification can efficiently avoid the gain-shaping disturbance to self-similar evolution is identified forthe first time. By use of this, self-similar amplification beyond the gain bandwidthlimit is realized in a2m-long Yb3+-doped photonic crystal fiber, generating37fstransform-limited pulses with a23.5W average power and287nJ pulse energy,which are the shortest pulses ever extracted from self-similar amplifiers.5. An all-fiber self-similar chirped-pulse amplification system is experimentallyinvestigated. The system generates0.9μJ transform-limited pulses, with a <115fspulse duration and~6MW peak power at a variable repetition-rate from2MHz to500kHz. It can be employed in directly writing photonic crystal waveguides.6. A numerical model with amplified spontaneous emission is developed andapplied to study the noise and gain properties of Yb3+-doped fiber chirped-pulseamplification systems. It is proposed that by use of the inherent gain-shaping effect,the fiber amplification system itself could recover the initial Super-Gaussian pulsesunder the largest gain and signal to noise ratio. In a proof-of-principle two-stagesystem, using the gain-shaping effect of pre-amplifier to pre-compensate pulsedistortions in the main-amplifier, Super-Gaussian pulses with a20nm spectralbandwidth and20ps temporal duration are recovered under a27dB gain.
Keywords/Search Tags:femtosecond laser, self-similar amplifier, chirped-pulse amplification, gain-shaping effect, Yb3+-doped fiber
PDF Full Text Request
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