A wide range of mechanisms is available for achieving rapid optical responsivity in material components. Amongst them, some of the most promising for potential device applications are those associated with an ultrafast response and a short cycle time. These twin criteria for photoresponsive action substantially favor optical, over most other, forms of response such as those fundamentally associated with photothermal, photochemical or optomechanical processes. The engagement of nonlinear mechanisms to actively control the characteristics of optical materials is not new. Indeed, it has been known for over fifty years that polarization effects of this nature occur in the optical Kerr effect – although in fluid media the involvement of a molecular reorientation mechanism leads to a significant response time. It has more recently emerged that there are other, less familiar forms of optical nonlinearity that can provide a means for one beam of light to instantly influence another. In particular, major material properties such as absorptivity or emissivity can be subjected to instant and highly localized control by the transmission of light with an off-resonant wavelength. This presentation introduces and compares the key electrodynamic mechanisms, discussing the features that suggest the most attractive possibilities for exploitation. The most significant of such mechanistic features include the off-resonant activation of optical emission, the control of excited-state lifetimes, the access of dark states, the inhibition or re-direction of exciton migration, and a coupling of stimulated emission with coherent scattering. It is shown that these offer a variety of new possibilities for ultrafast optical switching and transistor action, ultimately providing all-optical control with nanoscale precision.
A wide range of mechanisms is available for achieving rapid optical responsivity in material components. Amongst them, some of the most promising for potential device applications are those associated with an ultrafast response and a short cycle time. These twin criteria for photoresponsive action substantially favor optical, over most other, forms of response such as those fundamentally associated with photothermal, photochemical or optomechanical processes. The engagement of nonlinear mechanisms to actively control the characteristics of optical materials is not new. Indeed, it has been known for over fifty years that polarization effects of this nature occur in the optical Kerr effect – although in fluid media the involvement of a molecular reorientation mechanism leads to a significant response time. It has more recently emerged that there are other, less familiar forms of optical nonlinearity that can provide a means for one beam of light to instantly influence another. In particular, major material properties such as absorptivity or emissivity can be subjected to instant and highly localized control by the transmission of light with an off-resonant wavelength. This presentation introduces and compares the key electrodynamic mechanisms, discussing the features that suggest the most attractive possibilities for exploitation. The most significant of such mechanistic features include the off-resonant activation of optical emission, the control of excited-state lifetimes, the access of dark states, the inhibition or re-direction of exciton migration, and a coupling of stimulated emission with coherent scattering. It is shown that these offer a variety of new possibilities for ultrafast optical switching and transistor action, ultimately providing all-optical control with nanoscale precision.
In the optical excitation of many nanoscale systems, the primary result of photon absorption is an electronic excitation that is typically followed by ultrafast relaxation processes. The losses associated with such relaxation generally produce a partial degradation of the optical energy acquired, before any ensuing photon emission occurs. Recent work has shown that the intensity and directional character of such emission may be significantly influenced through engagement with a completely off-resonant probe laser beam of sufficient intensity: the mechanism for this optical coupling is a secondorder nonlinearity. It is anticipated that the facility to actively control fluorescent emission in this way may lead to new opportunities in a variety of applications where molecular chromophores or quantum dots are used. In the latter connection it should prove possible to exploit the particle size dependence of the nonlinear optical dispersion, as well as that of the emission wavelength. Specific characteristics of the effect are calculated, and suitable experimental implementations of the mechanism are proposed. We anticipate that this all-optical control device may introduce significant new perspectives to fluorescence imaging techniques and other analytical applications.
Interactions between light and molecular matter featuring photon absorption are commonly associated with excitation of individual chromophores. Subsequent relaxation is achieved through numerous mechanisms, such as scattering and energy transfer to neighbouring chromophores. The efficiency of such processes depends on many factors, including the intensity and wavelength of the optical input, the absorption cross-section of the molecule and the relative orientation of molecular components. New photonic materials are developed on the principle that such factors are controllable, duly tailoring the system to suit new technological applications. The parameters that determine the linear response in multicomponent materials are typically assessed within the theoretical framework of classical optics. However, with improved interest and capability in fabricating nanoscale structures (especially those that exhibit quantum effects), it is becoming increasingly relevant to develop theory that more faithfully represents how individual photons engage with matter. In such constructs, the interaction of materials with optical waves and photons is highly dependent on local molecular environment, therefore surrounding structures and ancillary species exert forms of influence on the photophysical processes inherent within dielectric media. At optical wavelengths where the secondary structure displays little intrinsic optical absorption, the role of such components is often interpreted as modifying the input through a corrective local index of refraction. Although expedient in the discussion of bulk properties of a macroscopic medium, it is reasonably supposed at a local chromophore-photon level that optical mechanisms operate in a different fashion. Using a fully quantized approach to the representation of local molecular electronic structure and electrodynamics, this research develops rigorous theory and a corresponding physical interpretation of how photon absorption, scattering and energy transfer are modified by vicinal, non-absorbing chromophores. The results provide insight into the mechanisms achieved within multi-chromophore systems, highlighting factors that assist in the optimization of optical characteristics in designer materials.
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.
Ultrafast luminescence represents a frontier in optical materials science, bridging fundamental investigations of light–matter interaction and the development of next‐generation photonic devices. Enhancing the speed of luminescence has long been a central objective, with continued relevance in both fundamental and applied contexts. In advanced photonic systems, rapid light emission enables the realization of extremely bright and temporally precise optical signals. This capability is crucial for quantum information technologies, where single‐photon sources with short radiative lifetimes are essential, as well as for classical high‐speed optical communication and sensing platforms. This review highlights recent progress in accelerating the emission process by leveraging cooperative emission effects, resonator‐enhanced coupling, and nonlocal or multipolar interactions, incorporating the authors’ original contributions and perspectives. These advances have led to the realization of novel coherent and incoherent bright light sources, high‐efficiency single‐photon emitters, radiative processes robust against thermal dephasing, and photon generation from materials typically regarded as nonluminescent due to thermal relaxation or self‐trapping. These mechanisms from both theoretical and experimental perspectives are explored, and insights into their integration for future photonic architectures are offered.
Through photonic mechanisms based on near-field coupling, laser radiation can engage with resonant energy transfer in a variety of suitably designed materials and molecular structures. Energy that has been acquired, through the initial absorption of resonant laser light, undergoes transfer between chromophores only on the throughput of off-resonant light, the process known as laser-assisted resonance energy transfer. The comprehensive results that are presented here extend and generalize the theory for both single and dual beam configurations, producing results that are applicable to media of various types including doped crystals, heterogeneous multichromophore solids, and solutions. The detailed principles, here explained in terms of both energetics and optical selection rule criteria, are specifically illustrated for a variety of materials. It is shown how general application of the theory can facilitate the elucidation of experiments, by clearly interpreting the effects of laser polarization manipulation. On further analysis of the photophysical mechanisms it is also demonstrated that such effects represent an entirely practicable basis for optical switching and logic gate operation. The additional polarization selectivity afforded by a two-beam setup proves to allow the most complete system control. With such a configuration, there is considerable promise for the realization of new optically driven logic and molecular devices.
Resonance energy transfer (RET) is a near-field mechanism for propagating optical energy between particles with suitably matching frequency response. The process communicates electronic excitation between suitably disposed (donor and acceptor) dipoles in close proximity, activated on excitation of the donor. In a multi-component system the transfer of excitation between any given donor and acceptor is usually passive, and it competes with loss mechanisms such as radiative decay and the possibility of transfer to one or more other acceptors. It thus appears that any potential exploitation of RET for optical switching is compromised by the innate passivity of the process. Now it emerges that there is a direct, all-optical route to introduce the necessary control. In a system constructed to satisfy frequency-matching conditions, but designedly to inhibit RET by geometric configuration, the throughput of laser pulses can facilitate energy transfer processes that would otherwise be forbidden, by laser-assisted resonant energy transfer. Suitably configuring an arrangement of transition dipoles, it proves possible to design parallel planar arrays of optical donor and acceptor particles such that the transfer of energy from any single donor, to its counterpart in the opposing plane, can be switched by appropriate laser radiation. As the energy transfer is itself mediated electromagnetically, the device operates as an optical transistor. For simplicity, a pair of two-dimensional arrays is envisaged, each consisting of equally spaced, identical particles arranged on a square lattice. A detailed appraisal of the system, including a consideration of competing processes, suggests that this configuration offers a new basis for the design of optically activated nanoscale transistor arrays.