An achiral system bathed in an intense beam of circularly polarized light shows chiral behaviour which may be detected with an auxiliary beam of polarized light. In this paper, expressions are derived for differential absorption rates, optical rotation of a plane polarized probe beam and circular differential scattering intensities. The theory of these two, three and four photon processes is developed by using quantum electrodynamics in electric dipole approximation. Two types of circular dichroism are distinguished: (a) the transition exhibiting induced dichroism is one-photon allowed, with chirality induced by scattering of the laser beam, or (b) the transition is two-photon allowed with absorption of a photon from each beam. In both, the induced circular dichroism is linearly dependent on the intensity of the inducing beam. Circular dichroism of type (a) is also discussed from the dressed-molecule viewpoint, and it is shown how a canonical transformation may be used to recover the results more simply. The possibility of observing Doppler-free circular dichroism is indicated. The induced optical rotation is analysed as a two-state process with transitions involving change of polarization only. The angle of rotation is linearly dependent on the intensity of the intense beam; its sign depends on the helicity. It is shown that, for non-forward Rayleigh scattering of the probe beam in the presence of an intense beam of light, the scattering intensity depends on the relative helicities of the two beams, and the differential intensity is proportional to the incident intensities.