  The photodetachement of H- in a quantum well is investigated based on closed
orbit theory. It is found the distances between the ion and the two hard walls
modulate the cross section of photodetachment. For the hard walls perpendicular
the polarization of photons, the detachment spectrum displays a staircase
structure. The pattern of staircase is modulated by the ratio of distances from
the ion to the two walls while the distance controls step interval of the
staircase structure.
