Two-photon Absorption Of Light Research Articles

Межзонное однофотонное поглощение и его линейно-циркулярный дихроизм в кристаллах с учетом эффекта когерентного насыщения

The polarization, spectral and temperature dependences of the single-photon absorption coefficient of polarized radiation are calculated, and its linear-circular dichroism in crystals of tetrahedral symmetry is researched. In this case, the contribution to the coefficients of one- and two-photon absorption of light from the effect of coherent saturation of optical transitions is taken into account.

NONLINEAR ABSORPTION OF POLARIZED RADIATION IN CRYSTALS WITH A COMPLEX BAND

The matrix elements of one- and two-photon optical transitions from the subbands of the valence band and the spin-orbital splitting band to the conduction band are calculated, expressions are obtained for them depending on the polarization vector and light frequency, as well as on the band parameters of the crystal. Expressions are obtained for the spectral-polarization and spectral-temperature dependences of the coefficients of interband two-photon absorption of light and linear-circular dichroism in semiconductors of tetrahedral symmetry in the three-band Kane model. It is shown that in the spectral-polarization dependence of the total coefficient of two-photon absorption of linearly and circularly polarized light in InSb: firstly, all spectral-polarization dependences have an oscillatory character; secondly, as the light frequency increases, the oscillation amplitude increases; thirdly, for circularly polarized light, the oscillation becomes aperiodic. KEYWORDS: spectral, temperature and polarization dependence, optical transitions, linear-circular dichroism, two-photon absorption of linearly and circularly polarized light.

Межзонный двухфотонный линейно-циркулярный дихроизм в полупроводниках в приближении Кейна

Interband two-photon optical transitions are classified and expressions are obtained for the matrix elements in a narrow-gap semiconductor depending on the band parameters, degree of polarization, and light frequency. It is shown that the main contribution to two-photon linear-circular dichroism in narrow-gap semiconductors is made by optical transitions proceeding from the subband of light holes to the conduction band. The dependences of the partial coefficients of interband two-photon absorption of light, which differ from each other by the types of optical transitions, are analyzed depending on the degree of polarization of the light, and a quantitative analysis of the coefficient of linear-circular dichroism of two-photon absorption of light is carried out. Expressions are obtained for the spectral dependence of the coefficient of interband two-photon absorption of light in narrow-gap semiconductors in the Kane model.

Interband two-photon linear-circular dichroism in semiconductors in the Kane approximation

The dependences of the partial coefficients of interband two-photon absorption of light, which differ from each other by the types of optical transitions, are analyzed depending on the degree of polarization of the light, and a quantitative analysis of the coefficient of linear-circular dichroism of two-photon absorption of light is carried out. Expressions are obtained for the spectral dependence of the coefficient of interband two-photon absorption of light in narrow-gap semiconductors in the Kane model. Keywords: initial, virtual and final states, interband two-photon absorption of light, Kane's approximation.

Formation of solitons and realization of the superluminality effect upon femtosecond pulse propagation in a medium containing gold nanoparticles

Based on computer simulation, we demonstrate the possibility of formation of solitons upon propagation of a femtosecond laser pulse in a medium containing gold nanoparticles in the presence of two-photon light absorption. The solitons are formed when the laser pulse induces a positive phase grating. The speed of solitons substantially exceeds the speed of laser radiation propagating in a linear medium.

On the Theory of the Shift Linear Photovoltaic Effect in Semiconductors of Tetrahedral Symmetry Under Two-Photon Absorption

The ballistic contribution to the current of linear photovoltaic effect under two-photon absorption of light is calculated and theoretically analyzed for the semiconductors of a tetrahedral symmetry with a complex band structure consisting of two closely spaced subbands. The transitions between the branches of one band in cases of the simultaneous absorption of two photons and successive absorption of two single photons are taken into account.

The nonlinear effect of the composite influence of red and blue light on Escherichia coli viability

A non-linear dependence of the inhibition of E. coli cells is found when irradiated simultaneously with the blue and red regions of the spectrum at a power density of 100 mW/cm2. Such dependence is explained by the assumption of a cascade two-photon absorption of light by DNA molecules with an intermediate resonance at cellular chromophores, causing excitation and subsequent DNA damage similar to damage when exposed to UV radiation.

Characteristics of the initiation of the explosive decomposition of PETN by the second-harmonic pulsed radiation of a neodymium laser

The critical fluence of the initiation of the explosive decomposition of pentaerythritol tetranitrate (PETN) by the second harmonic of a neodymium laser (532 nm) is found to be 12.3 J/cm2. It is shown that, under these conditions, the nonlinear two-photon absorption of light takes place. The critical fluence of the initiation of PETN explosive decomposition in the two-photon absorption mode is calculated within the framework of the thermal explosion model (14.7 J/cm2), which indicates that the thermal mechanism of explosive decomposition is operative under these conditions.

Femtosecond Laser Irradiation of Plasmonic Nanoparticles in Polymer Matrix: Implications for Photothermal and Photochemical Material Alteration

We analyze the opportunities provided by the plasmonic nanoparticles inserted into the bulk of a transparent medium to modify the material by laser light irradiation. This study is provoked by the advent of photo-induced nano-composites consisting of a typical polymer matrix and metal nanoparticles located in the light-irradiated domains of the initially homogeneous material. The subsequent irradiation of these domains by femtosecond laser pulses promotes a further alteration of the material properties. We separately consider two different mechanisms of material alteration. First, we analyze a photochemical reaction initiated by the two-photon absorption of light near the plasmonic nanoparticle within the matrix. We show that the spatial distribution of the products of such a reaction changes the symmetry of the material, resulting in the appearance of anisotropy in the initially isotropic material or even in the loss of the center of symmetry. Second, we analyze the efficiency of a thermally-activated chemical reaction at the surface of a plasmonic particle and the distribution of the product of such a reaction just near the metal nanoparticle irradiated by an ultrashort laser pulse.

Two-photon absorption in - and -based fibres at a wavelength of

The nonlinear two-photon light absorption coefficients have been measured in an optical fibre with a quartz glass core and in a fibre with a germanosilicate glass core. The two-photon absorption coefficient measured at a wavelength of in the -based fibre multiply exceeds that for the pure quartz glass optical fibre .

Disruption of the Cox-1 gene slows repair of microscopic lesions in the mouse gastric epithelium

Cyclooxygenase-1 (Cox-1) contributes to gastric defense of healthy tissue, but the role in the protection of the gastric epithelium after minor, acute damage has been difficult to study in vivo. Using 710-nm two-photon light absorption to create microscopic gastric damage in anesthetized mice with the gastric mucosal surface surgically exposed and perfused on the microscope stage, the acute response of surface cells to injury could be monitored using in vivo microscopy within seconds after injury. Using exogenous (Cl-NERF) and endogenous fluorophores, extracellular pH and cell death were monitored in real time during the entire damage and repair cycle. Two-photon damage was initiated by scanning approximately 200 microm(2) of gastric surface cells with high laser intensity, causing rapid bleaching of NAD(P)H fluorescence in optically targeted cells. In both Cox-1(+/-) and Cox-1(-/-) mice, a similar initial damage area expanded to include bystander epithelial cells over the next 2-5 min, with larger maximal damage noted in Cox-1(-/-) mice. The maximal damage size seen in Cox-1(-/-) mice could be reduced by exogenous dimethyl-PGE(2). All damaged cells exfoliated, and the underlying epithelium was coincidently repaired over a time interval that was briefer in Cox-1(+/-) (12 +/- 2 min, n = 12) than in Cox-1(-/-) (24 +/- 4 min, n = 14) mice. Directly after damage, pH increased transiently in the juxtamucosal layer (maximal at 3-6 min). A smaller peak pH change was noted in Cox-1(-/-) mice (DeltapH = 0.3 +/- 0.04) than in Cox-1(+/-) mice (DeltapH = 0.6 +/- 0.2). Recovery to normal surface pH took longer in Cox-1(-/-) mice (27 +/- 5 min) than in Cox-1(+/-) mice (12 +/- 1 min). In conclusion, constitutive loss of Cox-1 leaves the gastric mucosa more prone to damage and slowed repair of microlesions.

Two-photon induced photodecarbonylation reaction of cyclopropenones

Irradiation of cyclopropenones (1a-c) with 800 nm pulses of ultrafast laser results in a photodecarbonylation reaction via nonresonant two-photon absorption of light.

3,5-bis[4-(diethylamino)benzylidene]-1-methyl-4-piperidone and 3,5-bis[4-(diethylamino)cinnamylidene]-1-methyl-4-piperidone: prospective biophotonic materials.

The structures of 3,5-bis[4-(diethylamino)benzylidene]-1-methyl-4-piperidone, C(28)H(37)N(3)O, (I), and 3,5-bis[4-(diethylamino)cinnamylidene]-1-methyl-4-piperidone, C(32)H(41)N(3)O, (II), have been characterized. Because of conjugation between donor and acceptor parts, the central heterocycles (including the carbonyl group) in (I) and (II) are flattened and exhibit a 'sofa' conformation, with a deviation of the N atom from the planar fragment. The dihedral angles between the planar part of the heterocycle and the two almost flat fragments that include a phenyl ring and bridging atoms are 23.2 (1) and 11.2 (1) degrees in (I), and 11.8 (1) and 8.7 (2) degrees in (II). One- and two-photon absorption of light and the fluorescence of (I) and (II) have also been characterized.

Solvation effects on electronic excited states of methanol: A study of neat and mixed methanol/water clusters

Femtosecond pump-probe spectroscopic studies on mixed methanol/water clusters are presented. Two-photon absorption of light was employed to generate methanol molecules in the 3p Rydberg excited state, with transfer to the 3s Rydberg state during the ensuing dynamics. The experiments provide evidence that excited state hydrogen transfer occurs between a methanol molecule, which undergoes hydroxyl dissociation following electronic excitation, and a water molecule, leading to the involvement of a metastable H3O species.

Linear circular dichroism in nonlinear absorption of light in a quantum well

The far infrared absorption spectrum caused by optical transitions of holes between size-quantization subbands is calculated for p-GaAs/AlGaAs(001) quantum-well structures. The selection rules for optical transitions at the center of the two-dimensional Brillouin zone are determined. Allowance is made for resonant saturation of one-photon electronic transitions between size-quantized subbands of light and heavy holes. The linear circular dichroism in one-photon nonlinear (resonant) and two-photon absorption of light in a size-quantized well are investigated.

Polarization Dependences of Two-Photon Absorption in Narrow-Gap InSb and HgCdTe Type Semiconductors

Two-photon absorption of light in narrow-gap semiconductors of InSb and HgCdTe type is considered in the framework of the two-band Kane model. The analytical expressions for the TPA coefficient in dependence on the energies of pumped radiation and band gap of semiconductor is obtained. All the possible nonequivalent geometries of experiment are considered. In the calculations the excitonic effects are neglected. The polarization dependences are discussed and the comparison with experiment is carried out. [Russian Text Ignored].

Two-photon absorption of nonclassical light.

Two-photon absorption of light with nonclassical (squeezed) fluctuations is considered. Several unique effects are predicted for various possible regimes. These include a linear (instead of quadratic) growth of the absorption rate with the light intensity for weak fields, the possibility of a decreasing absorption with increasing intensity, and orders-or-magnitude differences between absorption rates for phase- and amplitude-squeezed beams of the same intensity.

Absorption of picosecond light pulses by selectively excited electronic molecular states

An investigation is made of the formation of single pulses and of pulse trains, and of selection of one or several pulses from a train by two-photon absorption of light in an excited system. Estimates and measurements are reported of the efficiency of a two-photon absorber used in combination with a onephoton saturable absorber. The results are also given of a probe-beam study of the kinetic processes in molecules.

Polarization characteristics of the two-photon absorption of light by trivalent rare earth ions in crystals

Polarization characteristics of the two-photon absorption of light by trivalent rare earth ions in crystals