Properties of a continuous optical discharge sustained by short-wave infrared laser radiation in high pressure argon

This paper is devoted to the experimental study of the characteristics of a continuous optical discharge (COD) sustained by high power continuous wave laser radiation at a wavelength λ = 1.08 μm in high pressure argon. New data on the COD threshold laser power dependence of argon pressure in the range 20–50 bar is obtained. The COD threshold laser power is shown to be in good agreement with the data obtained by other authors and theoretical evaluations provided the contribution of plasma energy loss due to thermal radiation is taken into account properly. The maximum plasma temperature was estimated to be 20–21 kk or higher, favorable to obtain high UV spectral radiance. A study of the convective plume oscillations around COD in argon has been carried out. It is found that in the pressure range 25–35 bars the growth of the laser radiation power leads to a decrease in convection oscillation frequency from 33 to 29 Hz, while the radius of the convective plume grows accordingly. The oscillation frequency ν and characteristic radius of the convective plume r₀ were found to obey the similarity relation ν=0.5g/2r0 previously established in experiments with COD in xenon. These results are promising for using COD in argon as a high brightness broadband UV radiation source.