Influence of the aperture angle on the efficiency of the melting of steel by millisecond laser pulses

The influence of the divergence and aperture of millisecond laser pulses on the efficiency, the dynamic characteristics, and the depth of the molten zone in steel under conditions ensuring the rapid growth of a vapour — gas channel was investigated experimentally. It was established that the dependence of the efficiency on the aperture angle passes through a maximum, the efficiency and depth-of-melting maxima being attained for an aperture angle of 75 — 80 mrad. The highest rate of growth of the vapour — gas channel is also achieved for these aperture angles. It is pointed out that this aperture angle is optimal and that it should be aimed at in the design of pulsed industrial laser systems.