On the competition between permanent dipole and virtual state two-photon excitation mechanisms, and two-photon optical excitation pathways, in molecular excitation

Jagatap, B. N.; Meath, William J.

doi:10.1016/0009-2614(96)00620-3

Cited by 30 publications

(27 citation statements)

References 27 publications

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“…Other techniques are also available for these types of problems including the generalized rotating wave approximation (GRWA), the precursor of the AGRWA, and the generalization of the two-level RWA to many-level molecules. [36][37][38][39] One approach for maximizing two-photon excitations is to seek molecules that lead to optimal excitation rates for the excitation from the ground state 1 to the excited state f via the permanent dipole excitation mechanism and then consider molecules with the desired or similar (1,f) framework and excited molecular states that add in the effects of the virtual state mechanism optimally and so it constructively 4,5,24,40 augments the contribution of the permanent dipole mechanism.…”

Section: -11mentioning

confidence: 99%

On the optimization, and the intensity dependence, of the excitation rate for the absorption of two-photons due to the direct permanent dipole moment excitation mechanism

Meath

2016

AIP Advances

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A model two-level dipolar molecule, and the rotating wave approximation and perturbation theory, are used to investigate the optimization and the laser intensity dependence of the two-photon excitation rate via the direct permanent dipole mechanism. The rate is proportional to the square of the laser intensity I only for small intensities and times when perturbation theory is applicable. An improvement on perturbation theory is provided by a small time RWA result for the rate which is not proportional to I2; rather it is proportional to the square of an effective intensity Ieff. For each laser intensity the optimum RWA excitation rate as a function of time, for low intensities, is proportional to I, not I2, and for high intensities it is proportional to Ieff. For a given two-photon transition the laser-molecule coupling optimizes for an intensity Imax which, for example, leads to a maximum possible excitation rate as a function of time. The validity of the RWA results of this paper, and the importance of including the effects of virtual excited states, are also discussed briefly.

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Section: -11mentioning

confidence: 99%

On the optimization, and the intensity dependence, of the excitation rate for the absorption of two-photons due to the direct permanent dipole moment excitation mechanism

Meath

2016

AIP Advances

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“…a two-state model may be applied. 15,16,18,20,[22][23][24][25][26][27][28][43][44][45][46][47][48][49][50][51][52] To be clear, the assumption is that the character of the fluorescence emission process, including the effect of the probe radiation, is dominated by two electronic levels; it is not to be presumed that the state from which the fluorescence decay occurs is necessarily the same as the state initially populated by photoexcitation. …”

Section: Two-level Systemsmentioning

confidence: 99%

Laser-Controlled Fluorescence in Two-Level Systems

Leeder

Andrews

2010

J. Phys. Chem. B

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The ability to modify the character of fluorescent emission by a laser-controlled, optically nonlinear process has recently been shown theoretically feasible, and several possible applications have already been identified. In operation, a pulse of off-resonant probe laser beam, of sufficient intensity, is applied to a system exhibiting fluorescence, during the interval of excited state decay following the initial excitation. The result is a rate of decay that can be controllably modified, the associated changes in fluorescence behavior affording new, chemically-specific information. In this paper, a two-level emission model is employed in the further analysis of this all-optical process; the results should prove especially relevant to the analysis and imaging of physical systems employing fluorescent markersthese ranging from quantum dots to green fluorescence protein. Expressions are presented for the lasercontrolled fluorescence anisotropy exhibited by samples in which the fluorophores are randomly oriented. It is also shown that, in systems with suitably configured electronic levels and symmetry properties, fluorescence emission can be produced from energy levels that would normally decay nonradiatively.2

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“…With the typical intensity levels of pulsed laser light, there arises a significant probability for two or more photons to interact simultaneously (within the limits of quantum uncertainty) with each optically distinct center. Although the materials that are most effective for the utilization of optical nonlinearity in frequency conversion (especially second harmonic generation, SHG) are those whose energy level structures are significantly more complex than atoms, the two-level approximation has received wide application in such a context [5,[11][12][13][14][15][16][17][18]; it not only delivers results of a relatively simple form, it also relates well to long-established concepts of chemical structure. A wealth of synthetic studies have built on the anticipated and oft-proven connection between 'push-pull' chromophore structures [19][20][21][22] (facilitating intramolecular electron transfer) and an enhanced second harmonic response.…”

Section: Introductionmentioning

confidence: 99%

Perturbation theory and the two-level approximation: A corollary and critique

Andrews

Coles

2011

Chemical Physics Letters

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a b s t r a c tThis analysis addresses the use of a two-level approximation to simplify expressions derived from perturbation theory. It is shown that the limitations of validity for the emergent results are more stringent than is commonly understood, being equivalent in effect to the adoption of a more extensive approximationone that significantly undermines the perturbative origin of those expressions. Effectively truncating the completeness relation, a series of interconnected operator relations comes into play, some with physically untenable consequences. A new theorem on the expectation values of operator functions highlights additional constraints upon any molecule modelled as a two-level system.

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On the competition between permanent dipole and virtual state two-photon excitation mechanisms, and two-photon optical excitation pathways, in molecular excitation

Cited by 30 publications

References 27 publications

On the optimization, and the intensity dependence, of the excitation rate for the absorption of two-photons due to the direct permanent dipole moment excitation mechanism

On the optimization, and the intensity dependence, of the excitation rate for the absorption of two-photons due to the direct permanent dipole moment excitation mechanism

Laser-Controlled Fluorescence in Two-Level Systems

Perturbation theory and the two-level approximation: A corollary and critique

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