Optical pressure applied to a semi-infinitive dielectric

The generally accepted notion about a magnitude of the optical pressure produced by a light wave on the boundary between free space and optical medium is absent at present. Moreover, it does not even know the direction of this pressure. We show that three kinds of pressures should be taken into account. This is the pressure arising due to a change of the momentum of the light wave on the boundary. This is the electrostriction pressure that does not change the momentum of the light wave. At last, these are the pressures arising in the regions of the optical medium where leading and trailing edges of a light pulse are propagating. The net pressure on the boundary is positive unlike zero pressure in accordance with the approach based on the Lorentz density force. Our consideration is based on grounds derived from unambiguous but contradictory results of two thought experiments. No advance assumption about types and a physical origin of optically induced forces responsible for the optical pressure is made. We have shown that the pressure produced by the continuous light wave at a steady state is negative. The total pressure produced by the light pulse on the boundary and on the optical medium is positive.