Thispaper is an attempt to reproduce predictions of quantum mechanics(QM) on probability of detection by starting with classical randomfield (e.g. random electromagnetic field). Thus it is an attemptto go beyond QM. The crucial point of our approachis that density operators of QM can be represented ascovariance operators of classical random fields. Born's rule can beobtained from measurement theory for classical random field under theassumption that the probability of detection of field is proportionalto the power of this field