A novel approach for the theoretical description of surface-relief formatio
n will be presented. The model is based upon statistical reorientation of s
ide chains in the polymer by repeated trans-cia-trans isomerisation process
es. It allows the explanation of surface-relief formation in different type
s of polymers. Furthermore the surface-relief formation in single-beam expe
riments as well as in intensity and in-phase grating experiments can be cal
culated. The described model does not need detailed assumptions on the micr
oscopic mechanism which deforms the polymer sample.