The power spectral density of the read signal for a magneto-optical readout system based on the polar Kerr effect has been analyzed. A criterion for optimum performance deriving from the signal to noise ratio is then defined and it is shown that a quadrilayer disk structure which acts as an interference device for the enhancement of the Kerr effect is superior to other structures. Results of a thermal calculation for the quadrilayer are then reported. These results clearly indicate that the quadrilayer can be designed to match different levels of laser power available for writing.