Laser self-focusing in the atmosphere

Abstract

The theory of self-focusing has been applied to beams propagating in the atmosphere. The effects of density variation, absorption, and air breakdown which limit the self-focusing through power driven instabilities are estimated. It is found that laser pulses whose pulse lengths are between 10 ns and 10 micros with powers from 10(2)P(c) to 10(3)P(c) have a chance to self-focus. Here P(c) is the critical power for self-focusing in an ideal nonattenuating medium with a nonlinear index of refraction.

High-energy femtosecond pulsed laser micromachining of thin film deposited silicon in self-focused air medium

“…26 An interpolation of this data for 800 nm gives rise to an approximate value of 3.5 (10 Ϫ24 ) m 2 /V 2 for n 2 . For air medium using a 1064 nm light, the nonlinear refractive index is 4.56 (10 Ϫ24 ) m 2 /V 2 .…”

“…The self-focusing of laser beams in nonlinear media such as air was introduced by Chiao et al, in the U.S. 17 and by Talanov in Russia 18 and continued by other researchers [19][20][21][22][23][24][25][26][27][28][29] with a large body of theoretical and experimental work using a variety of lasers such as ruby, Q-switched Nd:yttritiumaluminum-garnet ͑YAG͒, and mode-locked Nd:glass and Ti:sapphire. When an intense laser beam propagates through a nonlinear medium whose refractive index increases with field intensity, it creates its own optical waveguide and transmits without diffraction spreading.…”

“…26 These filaments can be further divided into hyperfine filaments before the beam is completely destroyed. Since the laser beam has an inherently nonuniform intensity distribution, the intensity-dependent indexes of refraction ͑␦n͒ causes different parts of the beam to propagate with different phase velocities.…”

“…26 In addition, attenuation phenomenon limits the self-focusing range and keeps the beam in- tensity below the breakdown threshold. However, in a real medium, such as air, self-focusing continues until the medium breaks down thus creating a plasma and stopping the beam.…”

Beam Quality of Annular Pulsed Laser Beams Propagating Through the Nonlinear and Dispersive Atmosphere

“…In these applications, the laser power is well above the critical power for self-focusing in air [5]. It is known that a steady-state channel of high-power laser beams may be formed when the Kerr self-focusing is compensated by diffraction [6][7][8][9], but the beam collapse will take place when the beam power is over a threshold critical power [9]- [11]. However, the beam collapse can be avoided for propagation from the ground or from space orbits through Earth's atmosphere to space orbits or to the ground because the self-focusing length exceeds the atmosphere thickness even if the laser power is much higher than the critical value [5] [12] [13].…”