Direct measurement of a beam force exerted to a foil with a laser displacement meter

The interaction of a beam with a target foil is studied using a torsion bal ance. The change in equilibrium angle of the target frame due to momentum t ransfer of the projectile was measured by a laser displacement meter. The t hick foil result can be interpreted in a straightforward way. On the other hand, the thin foil result shows that the momentum transfer to the target i s 71 +/- 10% of that expected from energy loss of a projectile.