Second Harmonic Generation Light Research Articles

Optical second harmonic generation from thin silver films

In this work, silver films of various thicknesses from 1 to 180 nm are vacuum evaporated on microscopic glass plates. The external reflection (ER) measurement of the second-harmonic generation (SHG) indicates that the peak intensity decreases dramatically as the film thickness is reduced below 20 nm and the incident angle yielding maximum SHG shifts toward lower values. The theoretical calculation based on the hydrodynamical model with excitation and interference of multiple reflections on both surfaces of the metal film can successfully address the salient features of these observations. Enhancement of the SHG light occurs only for film thickness as small as 15 nm, where the granular structure is obvious as observed from an atomic force microscope.

Azimuthal instabilities and self-breaking of beamsinto sets of solitons in bulk second-harmonic generation

The authors investigate numerically the process of second-harmonic generation of light in bulk quadratic nonlinear media with input beams containing phase dislocations. The authors find that above a threshold light intensity, the input beams self-split into several pieces along the azimuthal direction and form sets of spatial solitons.

Second-harmonic generation by intense beams containing phase dislocations:self-breaking into sets of solitons

Second-harmonic generation of light in bulk quadratic non-linear media with intense input beams containing phase dislocations is studied numerically under conditions for TypeI phase-matching. We investigate how, above a threshold light intensity, the input beams self-split along the azimuthal direction into a pattern of separate beams which then form a set of spatial solitons. The mechanism of such a behaviour is the azimuthal modulational instability of the ring-shaped, mutually trapped fundamental and second-harmonic beams containing the phase dislocations.

Multiple-scattering effects in the second-harmonic generation of light in reflection from a randomly rough metal surface

We present a rigorous numerical simulation analysis of the second-harmonic generation of p-polarized light in reflection from a one-dimensional, randomly rough, metal surface when the plane of incidence is perpendicular to the generators of the surface. When the incident light cannot couple to surface electromagnetic waves supported by the metal surface at the fundamental frequency, the angular distribution of the intensity of the incoherent component of the scattered light at the harmonic frequency displays either well-defined peaks or dips in the retroreflection direction and in the direction normal to the mean plane of the surface. These effects are suppressed by the direct excitation of surface polaritons at the fundamental frequency.

Optical methods to characterise the composition and homogeneity of lithium niobate single crystals

A number of the physical properties of lithium niobate strongly depend on sample composition. Although several procedures for the determination of the composition have already been published, a critical survey and an introduction to standard methods recommendable also for laboratories active in R&D of LiNbO3 devices is still missing. Within a detailed description of a series of methods, we summarise their capabilities and accuracy. The proposed optical characterisation methods, in particular those based on the generation of second harmonic light and those involving the measurement of birefringence and the UV absorption edge are found to be most convenient for an accurate and fast standard characterisation of LiNbO3 single crystals. An absolute accuracy of 0.1 mol% based on a comparison with the Curie temperature calibration method and a relative accuracy of up to 0.01 mol% are available. Some of these methods are also suited for the two or three dimensional homogeneity control of LiNbO3 single crystals.

Induced noncolinear frequency doubling: A new characterization technique for electro-optic crystals

Induced noncolinear frequency doubling (INCFD) is presented as a new characterization technique for electro-optic crystals. Using the interaction of two noncolinear laser beams for the generation of second harmonic light, the method yields a three-dimensional spatial resolution. First experimental results of INCFD measurements on composition gradients in lithium niobate and on the spatial orientations of 90o-domain walls in potassium niobate are shown.

Coherent optical processes of 1s ortho-excitons in Cu 2O by two-photon excitations

Emission spectra of natural single crystals of Cu 2O are examined under a two-photon excitation of 1s ortho-excitons of yellow series in degenerate regime at 2K. It is found that a second harmonic generation (SHG) via an electric quadrupole transition followed by a two-photon electric dipole transition and a hyper-Raman scattering process accompanied with 1LO ( Γ 12 −)-phonon are enhanced resonantly by the 1s ortho-exciton level. The integrated intensities of the SHG light is analyzed as a function of the excitation photon energy giving a phenomenological damping constant of the 1s ortho-exciton.

High-transparency films for nonlinear integrated optics based on P(VDF-TrFE) and poly(?-methyl styrene) host materials

In search of waveguiding polymer films with both highly efficient NonLinear Optical (NLO) and optimum transmission properties the second harmonic generation of light is measured on poled films of P(VDF-TrFE) blended with 10% PMMA or covered by the polarizable guest-host system PαMS, both pure and doped with 2% NLO dye The PαMS films turn out to be stable electrets after annealing at about 50°C and poling at room temperature. They are thus particularly easily processable candidates for NLO and waveguiding applications.

Reduction of optical chaos by a quantum correction in second-harmonic generation of light.

We consider the dynamics of second-harmonic generation of light in the context of chaos and order. The system is driven and dissipative. A Lyapunov analysis of chaos, and bifurcation maps, are presented and studied versus quantum corrections. We observe a reduction of chaos in the quantum case as well as suppression of basins of attraction. The role of damping is determined.

Organic superlattices with interface Fermi resonance: optical nonlinearity

A mechanism of optical nonlinearity of organic superlattices is considered which is based on the Fermi resonance between molecular excitations of alternating layers. Using Green's function formalism we have obtained a closed equation for the energy states in the vicinity of the Fermi resonance and found a general expression for the second-order nonlinear polarizability which determines the second-harmonic generation of light caused by the interface Fermi resonance coupling.

Nonperturbative resonant second harmonic generation: the strong field limit

A nonperturbative theory of second harmonic generation of light scattered by a three-level system with two resonant transitions for incoming field is presented. The existence of five lines in the second harmonic spectrum is predicted and the positions and integral intensities of the lines are calculated.

Nonperturbative resonant second harmonic generation: the weak field limit

A nonperturbative theory of second harmonic generation of light scattered by a three-level system with two resonant transitions for the fundamental field is constructed. Within the framework of the theory developed a nonlinear medium is considered to be a dynamical subsystem. The cross section for the scattering channel associated with the creation of second harmonic photons is calculated in the limit where the incident field is weak.

Chaos and order in second-harmonic generation: Cumulant approach.

We analyze some aspects of the cumulant method for second-harmonic generation of light in the context of the numerical results of Schack and Schenzle [Phys. Rev. A 41, 3847 (1990)] and earlier papers. The cumulant method can be useful in studies of the modifications introduced by quantum mechanics into classical systems which manifest chaotic oscillations. This problem is frequently referred to as ``quantum chaos.''

Interference second harmonic generation investigation of the chromophore orientation of hemicyanine dye molecules in a Langmuir-Blodgett monolayer

A novel method designed to determine the chromophore orientation in a Langmuir-Blodgett (LB) monolayer of hemicyanine dye by second harmonic generation (SHG) is reported. A hemicyanine LB monolayer was deposited on one side of a glass substrate and a stilbazium salt monolayer, whose chromophore orientation was known, was deposited on the other side as a reference. We have observed the interference patterns of the transmitted SHG light fields from both layers when the substrate was rotated. We found that the second-order non-linear polarizability β of hemicyanine dye is in the opposite sense in relation to that of stilbazium salt. Our experimental outcome confirms that the −N(CH 3) 2 group of hemicyanine dye points to the hydrophilic glass substrate.

Second-harmonic generation of light in ferroelectric polymer films with a spatially nonuniform distribution of polarization

In the present work, the author addresses the problem of whether it is possible to decide with second harmonic generation experiments if a given pyroelectric polymer film has a homogeneous distribution of polarization and how the limitations of second harmonic generation can be simply overcome by quasi-phase matching techniques and by optical resonance enhancement. A spatial distribution of the spontaneous polarization P/sub s/(z) results in a similar spatial distribution of the nonlinear optical coefficients d/sub 31/(z) and d/sub 33/(z). It is shown that the generated second harmonic power from a nonlinear slab is sensitive to this distribution of d/sub 31/ and d/sub 33/. It is further shown that the limitations of second harmonic generation which are due to the coherence length can be overcome by quasi-phase-matching and optical resonance enhancement for the fundamental or the harmonic beams. >

Chaos in second-harmonic generation of light. The case of a train of pulses

A numerical analysis of second-harmonic generation in an optical cavity pumped by an external train of pulses is performed. The duration of the pulses is a critical parameter which governs the existence of chaos. To indicate regions of chaos and order, the maximal Lyapunov exponents are used. Limit cycles and chaotic attractors are presented.

Second harmonic generation at metal surfaces: influence of surface charge

The longitudinal second harmonic generation of light at simple metal surfaces is determined within an extended Thomas-Fermi theory. A modified Smith ansatz for the electron density is shown to be appropriate to describe the nonlinear optical response of the surface. The dependence of second harmonic response on an additional surface charge is found. Negative surfaces generate the second harmonic much more efficient than positive ones.

Second harmonic generation at metal surfaces: influence of surface charge

The longitudinal second harmonic generation of light at simple metal surfaces is determined within an extended Thomas-Fermi theory. A modified Smith ansatz for the electron density is shown to be appropriate to describe the nonlinear optical response of the surface. The dependence of second harmonic response on an additional surface charge is found. Negative surfaces generate the second harmonic much more efficient than positive ones.

Reflection and transmission in second harmonic generation of light in KDP crystal

AbstractThe intensity of second harmonic light beams generated in potassium dihydrogen phosphate (KDP) crystals immersed in the optically denser fluid I‐bromonaphthalene has been observed as a function of the incident angle of the fundamental beam of the neodymium‐glass laser. The laser pulses are polarized in the [110] direction with respect to the KDP crystallographic axes. We observed for the first time that there is no transmitted second harmonic light at normal incidence when the nonlinear polarization PNLS(2w) lies in the direction [001] along the crystal face normal. Furthermore, the noncollinear phase‐matching condition where the two incident fundamental beams are on the opposite side of the face normal is demonstrated. The results agree well with the theory of Bloembergen and Pershan.

Lyapunov analysis of chaos in a system governing second-harmonic generation of light

Chaos in a system producing second-harmonic generation of light is analysed from the maximal Lyapunov exponent point of view. The influence of the amplitude modulation parameter on the degree of chaos is considered. Phase portraits are presented.