SELF-FOCUSING EFFECTS ASSOCIATED WITH LASER-INDUCED AIR BREAKDOWN

Sparks produced by focusing the beam from a single-mode ruby laser have been investigated, and photographs of radiation scattered at 90 to the incident beam show that breakdown occurs in filaments or points having a diameter of 5 μ or less. Intense pulses of coherent radiation scattered in the forward direction have also been observed, and the measured divergence of this light indicates the presence of self-focused regions having a diameter of ∼1.7 μ. These observations support the hypothesis that self-focusing of the beam may initiate laser-induced breakdown. © 1968 The American Physical Society.