Propagation And Amplification Of The Ultrabroad Bandwidth Laser

With the rapid development of laser technology in the past decade, the production of extremely short and intense laser pulses have been made, containing only a few optical cycle, even less a optical cycle. The propagation equation governing the evolution of the optical pulse plays a key role in nonlinear optics. In this thesis, we will investigate the nonlinear propagation and amplification of the broad bandwidth pulse laser (longer than one optical cycle pulse). Then we derive an equation for the evolution of the ultrabroad bandwidth pulsed beam (sub-cycle pulse ) in dispersive and nonlinear medium, and discuss its solving methods and propagation characterization.In the thesis, the conception "optical cycle " is worth noting. An optical cycle is that the pulse width is equal to the time period of the pulse center frequency. Our work and conclusions are mainly follows:I. Investigate the amplification theory of the broad bandwidth pulse, and make it be able to analyze the amplification in the in-homogeneously broadening medium. Discuss the probability of the pulse compensation in large-scale and high-quality, high power, and high energy laser system.The amplification of high chirped pulse with ultrabroad bandwidth has been investigated. The theoretical model of the pulse amplification in homogeneously broadening medium has been extended. The extended model is the basis to build the model of the amplification in homogeneously broadening medium. When the chirp is very big, C>>1, the pulse and the spectrum have very similar profiles, and the time and frequency satisfy the linear relation. The highly chirped pulse can be divided into many narrow-band pulses, in which every one have different center frequency and different intensity. So we have extended the theoretical model of the pulse amplification from the quasi-monochromatic approximation to ultrabroad bandwidth.Our model can be used to investigate the amplification of highly chirped pulse in homogeneously broadening medium and in inhomogeneously broadening medium. In addition, the effects of the homogeneously broadening and inhomogeneously broadening on amplification have been analyzed. For homogeneously broadening medium, the degree of gain narrowing is higher for the pulse with larger bandwidth. But the completely inhomogeneously broadening medium can be used as homogeneously amplification without distortion. The gain narrowing arises for broadband pulse in chirped pulse amplification, but it corresponds to the lineshape of the inhomogeneously broadening amplifier, and the distortion in inhomogeneously broadening medium is more regular than that in homogeneously broadening medium. The model for the highly chirped pulse can be used to evaluate the laser-performance, and optimize the laser designing, and it can offer greatly enhanced design freedom and reliability of the large-scale and high-quality, high power, and high energy laser system.II. Study the the propagation of the broad bandwidth pulse in nonlinear medium, and analyze its characteristic from the whole self-focusing to small scale self-focusing. At last, we theoretically investigate the nonlinear propagation of a highly chirped pulse.We have studied the the propagation of the broad bandwidth pulse in nonlinear medium by the (3+1) nonlinear Schrodinger equation, and analyzing its whole self-focusing. We have extended B-T theory to the case when the medium has obtained by (3+1) nonlinear equation. An exact analytic solution to the small-scale self-focusing equation is obtained in the case of small signal gain, and numerical simulations on the equation are performed in the case of saturating gain, comparing with the narrow bandwidth pulse.Based on the numerical simulations in microstructured optical fiber, we theoretically investigate the nonlinear propagation of a highly chirped pulse. Surprisingly, but interestingly supercontinuum can be efficiently generated with chirped pulse. Comparing with the case of Fourier-transform limited femtosecond laser, the chirped pulse with same peak power and initial bandwidth can produce broader supercontinuum spectrum with higher average power. Supercontinuum generationby the chirped pulse may provide a new method to directly produce high power ultrashort pulse that has an ultrabroad bandwidth much larger than that of the pump pulse.The effect of the pulse energy is important to broaden spectrum when having the same input bandwidth, and the highly chirped pulse having more energy can produce more broad with high average power spectrum. The chirped pulse is affected by similar physical effects as the chirp-free pulse, in which the importance of every effect can change, such as HOD is more important. The stretched and amplified pulse can be used to generate higher intense and more broad spectrum. Because it is difficult to amplify the ultrabroad band pulse now, the ultrashort pulse with higher intensity produced by this technique is potentially important. We believe that suitable design of microstructured fibers and utilizing the stretched and amplified chirped pulse could offer a new possibility producing new higher intensity ultrashort pulse.III. Propagation of the ultrashort pulse beam with ultrabroad Bandwidth have been discussed. We derive an equation for the evolution of the ultrabroad bandwidth pulsed beam (sub-cycle pulse ) in dispersive and nonlinear medium , and discuss its solving methods and propagation characterizationThe bandwidth of pulse is more important than the duration because of the chirp as a criterion for applying appropriate approximation and propagating equation. Though the duration rp of the chirp pulse is several times of the optical cycle, the center frequency is bigger than the carrier frequency, and the bandwidth may be is the several times of the carrier frequency. We have to introduce the frequency width of the spectrum by Fourier transform to analyze the pulse, not simply the duration of the pulse.Then the pulsed beam with ultrawide bandwidth have been discussed, where the bandwidth may be several times of the carrier frequency in numerical value. At this condition the concept of the envelope and the carrier frequency is useless, and the pulse have to be analyzed as a whole, where have no quickly or slowly part of the SEVA or SEWA. At the condition the propagation equation of the pulsed...