Shielding effects in interaction of nanosecond laser pulses with solid target

We present experimental study of radiation absorption in copper plasma created by Nd:YAG laser fundamental (1064 nm) harmonic. Absorption is recorded by monitoring attenuation of HeNe laser (633 nm) illuminating plasma side on. Assuming that inverse bremsstrahlung is dominant process, absorbtion of the Nd:YAG 1064 nm wavelength is evaluated relying on measurements conducted at 633 nm specific for He–Ne laser and using common analytical expressions. Radial profile of the absorption, the absorption coefficient, is deduced applying inverse Abel transform. The absorption is measured for several distances from the copper target and for various delays at each position. This procedure is repeated for three different energies of 1064 nm wavelength. It is shown that for high laser energies in IR domain absorption of radiation in the plasma is, within accuracy of the experiment, close to 92% while for lower energies considerable amount of the laser energy reaches the target surface. The absorption of the plasma attains its maximal value after the maximum of the laser power and remains at this value for couple of nanoseconds after the laser pulse ceases. It is also found that total energy absorbed by the plasma depends linearly on total incident energy in the investigated range of energy.