Theory of Nonlinear Optical Resonances Induced by Collisions

Abstract

It has been suggested by Bloembergen [1] that new resonances should appear in four-wave mixing processes in the case of large damping. These resonances occur when the difference between the frequencies of two beams is equal to a Bohr frequency for two atomic levels which are not directly populated by the light excitation. They have recently been observed by Bloembergen and his coworkers [2]. The original treatment of Bloembergen [1] was performed with the optical Bloch equations. It is well known that the validity of these equations is restricted to a small frequency range where the impact approximation can be applied [3]. We present here the theory of these resonances using the dressed-atom model [3]. The two main advantages of the present theory [4] are (i) a larger range of validity, (ii) a direct comprehension of the physical origin of these resonances.