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[en] Equations describing second-harmonic generation under quasi-phase-matched interaction conditions in crystals with a regular domain structure are derived. It is shown that appropriate substitution of variables makes these equations exactly identical with those describing second-harmonic generation in the usual homogeneous crystals. This analogy is used to obtained an expression for the second-harmonic amplitude in the case of inexact quasi-phase-matched interaction. (nonlinear optical phenomena and devices)
[en] The method of complete reconstruction of attosecond bursts has been demonstrated for attosecond high-harmonic pulse trains. The retrieved harmonic field provided detailed information about the envelope and the individual attosecond pulses contained in the attosecond pulse train. The time-frequency analysis revealed complicated spectral chirp structures and the contribution of different quantum paths to attosecond pulse formation.
[en] A method for generating non-uniformly spaced (chirped) trains of high-energy, high-contrast, femtosecond pulses is described and demonstrated. In this method a temporally stretched laser pulse is passed through an acousto-optic programmable dispersive filter (AOPDF), a birefringent plate, and a linear polarizer. It is demonstrated that linear and nonlinear variation of the pulse separation within the train may be controlled by changing respectively the third- and fourth-order dispersion introduced by the AOPDF. Programmable, non-uniform pulse trains of this type may find applications in quasi-phase matching high-harmonic generation
[en] Complete text of publication follows. The present paper investigates the relativistic self-focusing of elliptical laser beam in underdense plasma and its effect on plasma wave and second harmonic generation. When intense laser beam interacts with plasma, then transverse intensity gradient is established on account of redistribution of carriers. This transverse intensity gradients results in generation of plasma wave and pump wave frequency. The generated plasma wave, in turn, interacts with the input laser beam and leads to generation of a second harmonic. Effect of relativistic self-focusing on the amplitude of plasma wave and second harmonic yield are also analyzed.
[en] The Conference on Super Intense Laser Atom Physics (SILAP) was held in November 2003 in Dallas, Texas. The venue for the meeting was South Fork Ranch in the outskirts of Dallas. The topics of the meeting included high harmonic generation and attosecond pulse generation, strong field interactions with molecules and clusters, particle acceleration, and relativistic laser atom interactions
[en] A comprehensive study on the requirements for the highly efficient third harmonic generation (THG) and its inverse process, one-third harmonic generation (OTHG), in lossy waveguides is proposed. The field intensity restrictions for both THG and OTHG caused by loss are demonstrated. The effective relative phase ranges, supporting the positive growth of signal fields of THG and OTHG are shrunken by the loss. Furthermore, it turns out that the effective relative phase ranges depend on the intensities of the interacting fields. At last, a modified definition of coherent length in loss situation, which evaluates the phase matching degree more precisely, is proposed by incorporating the shrunken relative phase range and the nonlinear phase mismatch. These theoretical analysis are valuable for guiding the experimental designs for highly efficient THG and OTHG. (paper)
[en] In the first section we demonstrate the generation of four phase-locked harmonic pulses separated in time using frequency-domain interferometry. The spectra present a high sensitivity to a change of the relative phase on an attosecond time scale. The spectral resolution and the control of this relative phase could be used to perform high resolution measurements. In the second section we demonstrate temporal gating technique to isolate attosecond pulses. Recent results of such a gating showing a spectral broadening are reported. We show that this enlargement can unambiguously be attributed to a temporal confinement by a factor 2 of the harmonic emission
[en] A method of calculating 3-D Schroedinger equation for the application to the high-order harmonic generation is presented. The efficiency of the programming is crucial since huge amount of time and computer resources are required in this application. In the calculation, a hydrogen atom interacting with the strong incident laser field is being studied. Since it has a long range Coulomb potential, the behavior of the ionization cross-section is different from the case of some model potentials being studied by other groups for the calculation. The effect of the difference between two cases is also discussed. For the calculation of time varying wavefunction, the velocity gauge is used, which is known better than the length gauge calculation if the same number of radial basis functions is used. Since this study is to reduce the calculation efforts, we test the program running time for various number of radial functions and angular functions.
[en] This paper presents experimental evidence of enhancement of second-harmonic generation as a result of the combination of high electromagnetic mode density of states, low group velocity, and spatial phase locking of the fields near the photonic band edge
[en] Cascaded nonlinear phase shifts via second-harmonic generation are theoretically studied for quasi-phase-matched (QPM) structures. Both the effective phase mismatch and the structure itself contribute to the resultant nonlinear phase shift. Depending on the sign of the effective phase mismatch, structural contribution may enhance or depress the nonlinear phase shift. The fundamental wave will experience a nonlinear phase shift even if the effective phase matching is satisfied. By properly designing the effective phase mismatch, QPM structures with large material-based phase mismatch may provide large nonlinear phase shifts before saturation