Abstract

AM and FM modulation spectroscopies^1,2 have been used to study the properties of matter as well as for applications such as reading out optical memories.³ Advances in the accuracy of these methods have turned what used to be an academic subject, quantum noise, into a practical consideration. For example, memory readout fields must be very weak to keep the medium from heating up too much and quantum noise puts a lower limit on the readout field strength. Similarly if weak modulation sidebands are used to study coherent dips via AM spectroscopy, quantum noise becomes relevant. We use our quantum theory of multiwave mixing⁴ to predict the effects of quantum noise on these problems. We find that, for modulation frequencies about equal to the Rabi frequency for the strong wave, spontaneous emission contributes a pronounced AM component that might be confused with the appearance of a hole in reading out optical memories. In AM spectroscopy we find that the coherent dips are partly filled in by spontaneous emission.

© 1985 Optical Society of America