Metamaterial for efficient second harmonic generation

A theoretical study is carried out of the possibility of effective second-harmonic generation in a metamaterial representing a structure of alternating layers of semiconductor material with intrinsic and metallic conductivity that can be grown by epitaxial methods.     

Squeezing and photon antibunching in second harmonic generation: an analytical approach

With the help of second-order nonlinear interactions and hence Hamiltonian, we construct the equations of motion corresponding to pump and signal (second harmonic) fields in a second harmonic generation. The corresponding coupled differential equations involving the non-commuting field operators are not solvable in closed analytical forms. With the help of a perturbation method, we obtain analytical solutions of these field operators up to cubic orders in the interaction constant. In an appropriate limit (truncating the solution up to the second order in the interaction constant), these solutions lead to the existing solutions under the short-time approximation. The present analytical solutions are exploited to investigate the squeezing and the antibunching of photons of the input coherent light coupled to the said second-order nonlinear medium. We report the squeezing and antibunching effects of the pump field even for solutions up to the second order and hence the present results are consistent with earlier results. However, for the second harmonic mode, we report the squeezing involving the leading cubic term in the interaction constant.     

Optical second harmonic generation in a low-bandgap polymer

Recently, much research has been performed on developing low-bandgap polymers for e.g. harvesting solar energy. In the quest to improve these properties, little attention has been paid to their nonlinear optical properties, despite their interesting linear optical spectra and structural similarities to certain nonlinear optically active compounds. We characterized the optical second harmonic generation of corona poled films of poly(cyclopenta[2,1-b;3,4-b′] dithiophen-4-ylidenedioctylmalonate). The unexpectedly large nonlinear optical susceptibilities and the thermal and temporal stability of the material compare favorably to other novel nonlinear optical materials despite the lack of a donor-acceptor dye. Additionally, the polymer displays a very low absorption in the relevant wavelength region. These results demonstrate the promise of these materials for nonlinear optical devices.     

Optical second harmonic generation at platinum phthalocyanine-modified platinum electrodes

Optical second harmonic generation (SHG) has been used to observe changes within electronically conducting platinum phthalocyanine (PtPc) films deposited on polycrystalline platinum electrodes as the film undergoes electrochemical modification. PtPc-modified electrodes produced enhanced SHG responses over bare platinum surfaces. This is proposed to be due to an electric quadrupole contribution from the PtPc molecule. Examination of the polarization dependence of the SHG response reveals that electroactive PtPc molecules exist in environments both parallel and perpendicular to the electrode surface. It has been possible to observe redox processes occurring within the films by monitoring the magnitude of the SHG response with variations in potential. The decrease in SHG signal has been shown empirically to be proportional to the charge removed from the film during oxidation of the phthalocyanine (Pc) ring.     

Theory of second harmonic thermal-wave generation: One-dimensional geometry

The analysis of the thermal-wave second harmonic generation induced by the time-modulated heating of the material with temperature-dependent heat capacity C(T) and thermal conductivity k(T) is presented. The developed theory describes nonmonotonic behavior of the second harmonic amplitude in a semiinfinite medium. An enhanced spatial resolution of nonlinear photothermal imaging in materials with dominant role of the k(T) temperature dependence (i.e., for is predicted.On leave from International Laser Center, Moscow State University, 119899 Moscow, Russia.On leave from Jenoptik GmbH, Jena, Germany.     

Sensing with multipolar second harmonic generation from spherical metallic nanoparticles

We show that sensing in the nonlinear optical regime using multipolar surface plasmon resonances is more sensitive in comparison to sensing in the linear optical regime. Mie theory, and its extension to the second harmonic generation from a metallic nanosphere, is used to describe multipolar second harmonic generation from silver metallic nanoparticles. The standard figure of merit of a potential plasmonic sensor based on this principle is then calculated. We finally demonstrate that such a sensor is more sensitive to optical refraction index changes occurring in the vicinity of the metallic nanoparticle than its linear counterpart.     

Orientation-insensitive methodology for second harmonic generation. 1. Theory

The use of second harmonic generation as a means to probe either adsorption isotherms or the kinetics of adsorption/desorption is limited by the fact that the detected signal is dependent upon both surface coverage and molecular orientation. Thus, the second harmonic intensity must be tediously corrected if either the mean orientation angle or the width of the orientation distribution changes as a function of surface coverage. In this study, a new mathematical view of the second harmonic intensity as a function of excitation polarization is developed. This new approach predicts an experimental geometry that is relatively insensitive to molecular orientation, such that appropriate choice of the excitation polarization rotation angle allows for direct measurement of surface coverage. The theory is presented for the three common dominant hyperpolarizability tensor elements, beta(z'z'z'), beta(x'x'x'), and beta(x'x'z').     

Characterization of magnetization-induced second harmonic generation in iron oxide polymer nanocomposites

We have measured the magnetization-induced second harmonic generation (MSHG) of a nanocomposite consisting of iron oxide nanoparticles in a polymer film. The existing theoretical framework is extended to include DC magnetic fields in order to characterize the MSHG signal and analyze the measurements. Additionally, magnetic hysteresis loops are measured for four principal polarizer-analyzer configurations, revealing the P(IN)-P(OUT) and S(IN)-P(OUT) polarizer-analyzer configurations to be sensitive to the transverse magnetic field. These results demonstrate the use of MSHG and the applied formalism as a tool to study magnetic nanoparticles and their magnetic properties.     

A survey of ABX3 halides for optical second harmonic generation

A group of ABX₃ halides have been searched for nonlinear optical character by testing each for second harmonic generation in powdered samples using the method of Kurtz and Perry. It was found that most simple ternary halides do not produce second harmonic light and apparently have centrosymmetric structures. (CH₃)₄NHgCl₃, (CH₃)₄NHgI₃, (CH₃)₄NHgBr₃, KHgI₃·H₂O, and RbHgI₃·H₂O were found to produce SHG and the first two of these compounds were found to be phase-matchable.     

Sub-Poissonian photon squeezing and entanglement in optical chain second harmonic generation

Nonclassical properties exhibited by a chain of cavity modes second harmonic generation in coupled oscillators system, designed by using multichannel optical waveguides, is explored. The solution for the Hamiltonian of the coupled-modes driven by coherent excitation is obtained via an exact formulation of the normal-ordered Fokker-Planck equation. Nonclassical effects, namely the sub-Poissonian photons, squeezing and entanglement are noticed. Multichannel coupling of the coupled oscillators induces new possibilities for correlation between the modes in different channels, henceforth, provides an effective way towards manipulation of quantum light.     

Theoretical modeling on resonating the second harmonic for ultraviolet laser generation

The resonance of the second harmonic was proposed to improve conversion efficiency in ultraviolet laser. A schematic to generate the fourth harmonic laser with a compound cavity was modeled based on plane-wave approximation. The simulated results show that the mode-matching condition of the multi-mode lasers depends strongly on both frequency-mode spacing and resonator loss. In the case of the same cavity lengths and losses, the tolerance on the optical cavity length should be maintained on tens or hundreds of nanometer scales. Meanwhile, the TEM₀₀ beam can be achieved due to the best mode-matching at resonance and the beam size increases arising from the cavity detune.     

Guided-type second harmonic generation in ion implanted MgO:LiNbO3

Abstract

We report guided-type second harmonic generation (SHG) in Mg-doped lithium niobate optical waveguides. SHG in Mg-doped lithium niobate guide is as a comparable efficiency to the undoped lithium niobate waveguides [1] where the efficiency is 0.018% W^?1. We also report a better resistance to the impact of a high intensity pulsed laser at the in-couple facet.     

Surface second harmonic generation of Se–Te–Sb films

We present the first report for the investigation on surface second harmonic generation (SSHG) of thin films of Se_80−xSb_xTe₂₀ (0 ≤ x ≤ 9 at.%) system. SSHG measurements were made using a confocal microscope system and a mode locked Ti:Saphire pulsed laser (785 nm) probe beam with 100 fs pulses. A remarkable difference in the magnitude of the signal generated between the samples with antimony content ≤4 at.% and those containing antimony >4 at.% has been explained based on charge distribution associated with structural changes in these materials for different compositions. The results have been discussed on the basis of relatively isolated atomic events that occur at short length scales mainly due to spatial redistribution of covalent bonds and the rational changes in the electric dipole moment arising from the change in the distribution of the lone pair electrons inherent in chalcogenide glasses. The analysis of the results is supported by the variation of the glass transition temperature obtained from differential scanning calorimetry (DSC) results. The electronic structure has been calculated using the density functional theory (DFT) modified by the generalized gradient approximation (GGA) for the exchange correlation energy.