Theoretical Investigation Of Propagation Of Laser Beam And Ultrashort Pulsed Beam

In the thesis, the propagation of the laser beam and the ultrashort pulsed beam was investigated theoretically. The thesis analyzed variance matrix treatment to study the propagation and the focusing of paraxial light beam, coherent and incoherent off-axis elegant Hermite Gaussian beam combinations, and nonparaxial correction of propagation of free space ultrashort pulsed beam, and the latest development, of research on femtosecond nonlinear optics. The thesis is composed of five chapters, among which are, Chapter 1 is a survey, Chapter 2, 3, 4 are the overview of our own work, Chapter 5 is a conclusion and prospect.Chapter 1: A survey of the propagation of the laser beam and the ultrashort pulsed beam was introduced.Chapter 2: Using a so-called variance matrix, we studied the propagation and the focusing characteristics of the paraxial light beams. The quantities characterizing the gross features for a paraxial optical beam, such as the beam width, the divergence, the curvature radius of the wavefront, the complex beam parameter q. and the beam quality factor, are related by using variance matrix. The relation between the M2-factor and the determinant of variance matrix is also presented.Chapter 3: In this chapter, we study the nonparaxial pulsed beam solution. Specifically, the general lowest-order correction field is given in a integral form. Some special ' examples, such as the lowest-order correction to the paraxial approximation of a fundamental Gaussian beam, uniformly driven by a Gaussian pulse. Numerical simulation of our lowest-order correction solution and Porras' lowest-order correction solution shows that our lowest order correction produces a good accuracy to the paraxial exact solution. Chapter 4: Applying the definitions of the generalized second and fourth order moments, the beam propagation M2-factor and the kurtosis parameter of coherent and incoherent combinations of two-dimensional off-axis elegant Hermite-Gaussian (EHG) beams are derived analytically and numerically. And the power in bucket (PIB) is also presented numerically. Our results illustrate the propagation properties of the beam through a first-order optical ABCD system. A comparison of the irradiance for coherent and incoherent combination shows that the high peak irradiance can be obtained for coherent combination at the focal plane.Chapter 5: The latest development of research on femtosecond nonlinear optics is introduced in this chapter. Recent progress in ultrafast optics has allowed the generationof ulfcraintense light pulses comprising merely a few field oscillation cycles. The arising intensity gradient allows electrons to survive in their bound atomic state up to external field strengths many times higher than the binding Coulomb field and gives rise to ion-ization rates comparable to the light frequency resulting in a significant extension of the frontiers of nonlinear optics and (nonrelativistic) high field physics.