We show that a system characterized by long-lived coherent population oscillations (CPOs), such as a two-level system that decays via a shelving state, can be used to construct a spatial optical memory. In the presence of a cw control field, a field is generated at the four-wave mixing (FWM) frequency with the same spatial profile as the initial probe. When the control field is switched off, these spatial profiles are encoded in the CPOs of the ground and storage states. When the control field is switched on again, the probe and FWM fields are retrieved simultaneously with the same spatial profiles as the initial probe.

A method for the spatial separation of R-R and S-S homodimers from R-S heterodimers, where R and S are chiral molecules of opposite handedness ("enantiomers"), is introduced. The separation, achieved by using two spatially inhomogeneous time-delayed laser pulses, is a result of one type of dimer forming a "dark state" and experiencing no light-induced potential, while the other type of dimer, forming a "bright" state, undergoes deflection. The direction of deflection of the two types of chiral dimers may be reversed by reversing the time delay between the laser pulses. We demonstrate the feasibility of the process by simulating the separation of lactic acid dimers.

We show analytically and numerically that the application, during the storage time, of an additional weak field connecting the lower levels (LLs) of a Lambda system can modify the spin coherence and the amplitude of the retrieved probe without causing distortion. The LL coupling field adds an additional phase-dependent term to the probe propagation equation. The retrieved probe is amplified when the total relative phase Phi=0 or pi and decreased when Phi=pi/2.

We show analytically and numerically that a double-Lambda system, characterized by parametric amplification of cross-coupled probe and four-wave mixing pulses, is an excellent medium for producing both slow and stored light. Moreover, this system can compensate for the absorption and broadening processes that usually occur without destroying the coherent properties of the medium. The stored probe signal pulse is written by means of a simple Lambda system and is retrieved and amplified, at the same frequency, by a double-Lambda system that also produces a pulse at the four-wave mixing frequency.

We study the phase-dependent propagation of a strong, resonant pump and two weak symmetrically detuned fields in a two-level system with population decay through a cascade of intermediate levels.As this system forms a closed loop, the propagation is phase-dependent. For an initial total phase = 0, there is constructive interference between the two weak fields, leading to parametric amplification on propagation. When = π , destructive interference occurs, leading to absorption of the weak fields on propagation. When the weak fields are initially equal in intensity, and = 0, π, remains constant on propagation. For other initial phases, changes on propagation. Dramatic phase changes from π to 0 can occur when the weak fields are initially unequal in intensity and = π .