An interferometric study of CO2-1aser-produced sparks

The expansion of sparks produced in various gas mixtures by a helical TEA CO
2
laser of modest power (∼ 0.5 MW) has been examined using time-resolved photography and two-wavelength interferometry. The latter was accomplished with the aid of a synchronized ruby laser, the fundamental and second-harmonic frequencies of which illuminated a Mach-Zehnder interferometer. The interferograms have been analyzed using Abel inversion techniques and two-dimensional profiles of the electron density within the sparks obtained.