"Self-guided hot light pulse"

Presented by: Prof. See Leang Chin
Center for Potics, Photonics and Laser(COPL) & Department of Physics, Engineering Physics and Optics, Laval University, Quebec, Canata
　

Time: 10:30a.m.-11:30a.m., Thursday, June 17

Place: Seminar Room at 4th Floor (room No. 424-426)
RIKEN Main Research Building

Abstract

When a powerful femtosecond laser pulse propagates in an optical medium, it self-transforms into a white light laser pulse [1]. The spatial distribution of this white light pulse appears to a human eye as a self-guided structure, which contains a bunch of bright, white hot spots (light bullets) whose trails along their paths of propagation give the perception of many filaments. In the plane perpendicular to the propagation direction, these hot spots are surrounded by a background of light which we call rerservoir. Each of these hot spots is surrounded by a system of colorful rings, which create patterns changing dynamically as the propagation distance changes. The physics of the development of a mature filament includes self-focusing, material dispersion, plasma generation, intensity clamping and self-steepening  [2]. In the case of multiple filamentation, competition among filaments [3] for energy via field interference occur. The diameter of the pulse at the pump wavelength does not change practically during long distance propagation in air for at least up to the limit of our propagation distance of 100 m [4] so long as there is self-focusing balanced by plasma generation. This is because the self-focusing effect tends to limit the pulse from diverging through normal diffraction. The self-foci (balanced by plasma generation) dynamically and constantly change their positions inside the laser pulse. We call this a self-guided hot light pulse. We note that most of the laser energy is still contained inside the pump wavelength zone (reservoir) [4]. The potential applications in long distance propagation in air will be discussed.

References

[1] V.P. Kandidov, O.G. Kosareva, I.S. Golubtsov, W. Liu, A. Becker, N. Akozbek, C.M. Bowden, S.L. Chin, "Self-transformation of a powerful femtosecond laser pulse into a white-light laser pulse in bulk optical media (or supercontinuum generation)", Appl Phys B 77, 149-165 (2003)

[2] H. Schroeder, S L Chin, "Visualisation of the evolution of multiple filaments in methanol", Optics Communications, accepted.

[3] S.A. Hossein, Q. Luo, B. Ferland_, W. Liu, S.L. Chin, O.G. Kosareva, N.A. Panov, N. Aközbek, V.P. Kandidov, Competition of multiple filaments during the propagation of intense femtosecond laser pulses, submitted (2004).

[4] W. Liu, S. A. Hosseini, Q. Luo, B. Ferland, S. L. Chin, O. G. Kosareva, N. A. Panov and V. P. Kandidov, "Experimental observation and simulations of the self-action of white light laser pulse propagating in air", New J. Phys. 6, 1-22 (2004).