Formation of a continuous laser spark in air

A study was made of the growth of a laser spark created by focusing a giant laser pulse with an axicon. A spark appeared after 20–50 nsec, depending on its nature, and the radiation emitted by the spark plasma lasted for more than 100 μsec. The maximum diameter of the luminous region was 1 cm. The longitudinal and transverse spark expansion velocities were determined. Measurements were made using a laser-triggered image-converter camera which was specially designed for this purpose.