Laser-generated ions emitted in backward and forward directions from an 80 nm thick Sn film deposited on the soda lime glass were investigated in the range of laser fluence (93–521 J/cm2). The ion collectors operating in time-of-flight configuration were employed to measure charge density and energy of the Sn ions emitted in both directions. As expected, the charge density and peak energy of the ions emitted in backward direction were found to increase with the laser fluence: the ion charge density and peak ion energy increased by a factor of three and ten, respectively. In contrast, the charge density of the ions emitted in forward direction decreased and their energy did not seem to vary with laser fluence. The surface morphology of the beam spot at the film and substrate was examined with the help of an optical microscope. The heat conduction equation is numerically solved to simulate the temporal distribution of temperature at the surface and along depth of the Sn film. A model, based on the results of optical microscopy and computer simulation, is proposed to explain the peculiar behaviour of the charge density and energy of the ions emitted in forward direction.