Abstract
The theory of non-resonant optical processes with intrinsic optical nonlinearity, such as harmonic generation, has been widely understood since the advent of the laser. In general, such effects involve multiphoton interactions that change the population of each input optical mode or modes. However, nonlinear effects can also arise through the input of an off-resonant laser beam that itself emerges unchanged. Many such effects have been largely overlooked. Using a quantum electrodynamical framework, this review provides detail on such optically nonlinear mechanisms that allow for a controlled increase or decrease in the intensity of linear absorption and fluorescence and in the efficiency of resonance energy transfer. The rate modifications responsible for these effects were achieved by the simultaneous application of an off-resonant beam with a moderate intensity, acting in a sense as an optical catalyst, conferring a new dimension of optical nonlinearity upon photoactive materials. It is shown that, in certain configurations, these mechanisms provide the basis for all-optical switching, i.e., the control of light-by-light, including an optical transistor scheme. The conclusion outlines other recently proposed all-optical switching systems.
Highlights
Nonlinear optics is one of the most remarkable and pervasive fields to emerge from the development of the laser over 50 years ago
Nonlinear processes involve the concurrent absorption of multiple off-resonant photons—meaning that the associated rate depends on the square, or a higher order, of the corresponding input laser intensity
From the viewpoint of quantum electrodynamics (QED) [43,44], all optical interactions occur through the annihilation and creation of photons
Summary
Nonlinear optics is one of the most remarkable and pervasive fields to emerge from the development of the laser over 50 years ago. Overlooked is the fact that a moderately intense off-resonant laser beam (~1011 –1012 W cm−2 ) may provide a controlling effect on a resonant process such as fluorescence—acting as a stimulus with an optical frequency at which the molecule is transparent. In such a case, the beam is unaltered by the light-matter interactions that occur. If the resonant process is forbidden by virtue of selection rules or another symmetry constraint, it is possible that it can become entirely activated by the input beam, since the resultant nonlinear process may be allowed This is the potential basis for an all-optical switch. The concluding section provides a discussion of the context for deploying these and other schemes for all-optical switching
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