DYNAMICS OF LASER-PRODUCED SILVER PLASMA UNDER FILM DEPOSITION CONDITIONS STUDIED USING OPTICAL-EMISSION SPECTROSCOPY

Laser produced plasma from silver is generated using a Q-switched Nd:Y AG laser. Optical emission spectroscopy is used to carry out time of f light (TOF) analysis of atomic particles. An anomalous double peak pro file in the TOF distribution is observed at low pressure. A collection of slower species emerge at reduced pressure below 4 x 10(-3) mbar an d this species has a greater velocity spread. At high pressure the pla sma expansion follows the shockwave model with cylindrical symmetry wh ereas at reduced pressure it shows unsteady adiabatic expansion (UAE). During UAE the species show a parabolic increases in the expansion ti me with radial distance whereas during shock wave expansion the expone nt is less than one. The angular distribution of the ablated species i n the plume is obtained from the measurement of optical density of thi n films deposited on to glass substrates kept perpendicular to the plu me. There is a sharp variation in the film thickness away from the fil m centre due to asymmetries in the plume. (C) 1998 Elsevier Science B. V.