THE RESPONSE OF A TWO LEVEL EXCIMER MEDIUM TO TWO STRONG PUMP FIELDS AND ONE WEAK PROBE FIELD AT RESONANCE FREQUENCIES HAS BEEN INVESTIGATED. THIS FORMS A STUDY OF PHASE CONJUGATED WAVES AT 193 NM BY DEGENERATE FOUR WAVE MIXING (DFWM). THE NONLINEAR POLARIZATION INDUCED BY THE OPTICAL FIELDS IS TREATED IN A THEORETICAL ANALYSIS AS A SOURCE TERM IN THE WAVE EQUATIONS AND APPROXIMATE SOLUTIONS FOUND UNDER THE ASSUMPTION OF SLOWLY VARYING AMPLITUDES . THE PHENOMENON CAN BEBETTER UNDERSTOOD BY FULL QUANTIZATION OF THE ATOMIC MEDIUM AND THE RADIATION FIELD, REFLECTIVITIES OF 100% ARE CALCULATED BY THIS METHOD. (SHORTENED)