We study the photon production in a one-dimensional cavity whose left
and right walls oscillate with the frequency Omega(L) and Omega(R), re
spectively. For Omega(L) not equal Omega(R), the number of generated p
hotons by the parametric resonance is the sum of the photon numbers pr
oduced when the left and the right wall oscillates separately. However
, for Omega(L)=Omega(R), the interference term proportional to cos phi
is found additionally, where phi is the phase difference between two
oscillations of the walls.