Enhanced nonlinear optical conversion from a periodically nanostructured metal film

We demonstrate an approximately10(4) increase in conversion efficiency for optical second-harmonic generation (SHG) from a periodically nanostructured metal structure consisting of a single subwavelength aperture in a thin silver film surrounded by a set of concentric surface grooves. The forward-transmitted second-harmonic radiation from this structure is measured relative to that from an identical aperture with no surrounding surface periodicity. We explain the observed SHG enhancement quantitatively in terms of a measured 120x increase in the strength of the fundamental radiation in the vicinity of the aperture resulting from the periodic nanostructuring.     

Super-resolution scanning laser microscopy with a third-order optical nonlinear thin film

In a configuration of optical far-field scanning microscopy, super-resolution achieved by inserting a third-order optical nonlinear thin film is demonstrated and analyzed in terms of the frequency response function. Without the thin film the microscopy is diffraction limited; thus, subwavelength features cannot be resolved. With the nonlinear thin film inserted, the resolution is dramatically improved and thus the microscopy resolves features significantly smaller than the smallest spacing allowed by the diffraction limit. A theoretical model is established and the device is analyzed for the frequency response function. The results show that the frequency response function exceeds the cutoff spatial frequency of the microscopy defined by the laser wavelength and the numerical aperture of the convergent lens. The main contribution to the improvement of the cutoff spatial frequency is from the phase change induced by the complex transmission of the nonlinear thin film. Experimental results are presented and are shown to be consistent with the results of theoretical simulations. PACS 42.25.Bs; 42.50.St; 42.65.Hw; 42.65.Jx     

Resonant optical transmission through a one-dimensional photonic crystal adjacent to a thin metal film

We theoretically and experimentally reveal that the large resonant optical transmission (ROT) can be realized through a one-dimensional photonic crystal adjacent to a thin metal film, at a frequency in the original band-gap of the photonic crystal (PC). The influence of periodic number of PC and the thickness of the adjacent metal on the transmission frequency and intensity is studied in detail. An optimum design is given to reach the maximum transmission efficiency, meanwhile a mechanism underlining the ROT phenomenon is proposed. An effective admittance-matching theory is proposed to understand this effect and quantitatively determine the operating frequency, which matches very well with the simulated and measured results. The effects might be very useful to realize some optical filters and sensor devices since the structure is easy for mass production and is matured technically to be prepared in industry.     

Self-localization of excitons and nonlinear optical properties of J-aggregates in a periodically modulated thin film

Nonlinear optical properties of dye J-aggregates embedded in a one-dimensional periodic medium are analyzed theoretically and numerically. The effect of strain-induced exciton self-localization in a chain of monomers on nonlinear optical properties of the system is investigated for weakly and highly ordered J-aggregates. It is found that exciton self-localization in a periodic medium enhances light absorption and effective optical susceptibility. Optical bistability thresholds are examined for weakly and strongly excited dye J-aggregate thin films. It is shown that the threshold intensity of incident electromagnetic field is lower by more than an order of magnitude as compared to that for a homogeneous medium.     

Effect of an optical negative index thin film on optical bistability

We investigate nonlinear transmission in a layered structure consisting of a slab of positive index material with Kerr-type nonlinearity and a subwavelength layer of linear negative index material (NIM) sandwiched between semi-infinite linear dielectrics. We find that a thin layer of NIM leads to significant changes in the hysteresis width when the nonlinear slab is illuminated at an angle near that of total internal reflection. Unidirectional diodelike transmission with enhanced operational range is demonstrated. These results may be useful for NIMs characterization and for designing novel NIMs-based devices.     

A white-lighting LED system with a highly efficient thin luminous film

In this work, a highly effective white light-emitting diode (LED) system is realized by a combination of an LED and a photonic crystal (PC-) structured luminous film. The emission intensity of the PC-structured luminous film emission is enhanced by a factor of ca. 10.6 compared with that of the planar film. The light from the system can give rise to an intense white emission with CIE coordinates (0.33, 0.38). The total emission intensity is over twice greater than that of the usual LED system. Additionally, the emission of the PC-structured films can be switched flexibly. The strategy proposes an efficient and facile method for high excitation and extraction of the luminous film, and it shows great potential for a bright white lighting with excellent colour matching.     

The third order nonlinear optical characteristics of amorphous vanadium oxide thin film

We studied the nonlinear absorptive characteristics (saturation intensity threshold and effective nonlinear absorption coefficients) and nonlinear refraction in a 50-nm-thick VO _x thin amorphous film prepared by pulsed DC magnetron reactive sputtering. The absorptive and refractive nonlinearities were investigated by pump–probe and Z-scan techniques. The closed-aperture Z-scan results reveal self-defocussing characteristics of the amorphous VO _x thin film for both nanosecond and picosecond pulse durations. Experimental results show that a phase transition does not occur in the range of intensities used for the experiments and the investigated sample can be treated as an amorphous semiconductor structure. The open-aperture Z-scan curves with nanosecond pulses exhibit saturable absorption for all input intensities. On the other hand, the open-aperture Z-scan curves with picosecond pulses exhibit nonlinear absorption/saturable absorption for low/high input intensities, respectively. Saturation intensity thresholds were found to be 15.3 MW/cm² for 4-ns pulse duration and 586 MW/cm² for 65-ps pulse duration.     

Synthesis of CdZnO thin film as a potential candidate for optical switches

Cadmium doped zinc oxide thin films have been prepared using a thermal decomposition technique. The influence of Cd as a doping agent on the structure, optical and nonlinear optical properties was carefully investigated using X-ray diffraction (XRD), scanning electron microscopy (SEM) and a UV-vis spectrophotometer. A deep correlation has been found between the surface roughness and the optical properties. The roughness is found to deteriorate the nonlinear response, such that the highest nonlinear susceptibility χ⁽³⁾ is obtained for the smoothest layer. The third-order nonlinear susceptibility χ⁽³⁾ has been calculated using the Frumer model, and is estimated to be 3.37×10⁻¹⁰ esu. The dispersion of the refractive index of the prepared thin film is shown to follow the single electronic oscillator model. From the model, the values of oscillator strength (E_d), oscillator energy (E_o) and dielectric constant (ε_∞) have been determined. The conductivity has been measured as a function of the energy of the photons, revealing marginal change at energies below 3.15 eV, while above this value there is a large increase in the conductivity. This suggests that CdZnO is a potential candidate for applications in optical devices such as optical limiter and optical switching.     

Plasmonic sensors based on thick metal film perforated with rectangular nanohole arrays

The dependence of optical properties on the ambient medium, the period of nanohole arrays and the metal film thickness in a thick silver film perforated with rectangular nanohole arrays is investigated using the finite‐difference time‐domain technique. As a result of the coupling between top and down surface plasmon polaritons, mediated by localized surface plasmon resonances supported by the metallic rectangular nano‐ holes, interesting light phenomena are observed for varying thickness of the metal film and period of the rectangular nanohole arrays. Based on the dependence of the optical properties on the ambient medium, the possibility of exploiting thick metal rectangular nanohole arrays as plasmonic sensors is further discussed, the potential application as plasmonic sensors is revealed. (© 2013 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Laser acceleration of electrons in a thin metal film

A mechanism acceleration of electrons to relativistic velocities in a thin metal film irradiated with ultrashort (τ _L ≤1 ps) high-power (I>¹⁶ W/cm²) laser pulses is proposed. The acceleration is due to a resonance action of the nonuniform field on a portion of the electrons, viz., those which oscillate in the direction transverse to the film with a frequency close to the frequency of the field. Pis’ma Zh. éksp. Teor. Fiz. 66, No. 1, 8–12 (10 July 1997)     

Determination of optical constants and nonlinear optical coefficients of Violet 1-doped polyvinyl alcohol thin film

The optical properties of Violet 1-doped polyvinyl alcohol (PVA) have been investigated using Wemble and Didomenico (WD) method. The optical constants such as refractive index n, the dispersion energy E _d, the oscillation energy E ₀, the lattice dielectric constant \(\varepsilon _{\infty } \), light frequency dielectric constant ε ₀ and the ratio of carrier concentration to the effective mass N/m* have been determined using reflection spectra in the wavelength range 300–900 nm. The single- beam Z-scan technique was used to determine the nonlinear optical properties of Violet 1:polyvinylalcohol (PVA) thin film. The experiments were performed using continuous wave (cw) laser with a wavelength of 635 nm. The calculated nonlinear refractive index of the film, n ₂ = ?2.79×10^?7 cm²/W and nonlinear absorption coefficient, β = 6.31×10^?3 cm /W. Optical limiting characteristics of the dye-doped polymer film was studied. The result reveals that Violet 1 can be a promising material for optical limiting applications.     

Investigation the spectral scattering characteristics of a nanohole in a film

Based on the method of discrete sources, an analysis is made of the spectral scattering characteristics of a nanohole in a metal film applied onto a glass prism. An effect of extremal electromagnetic energy leakage through the hole is discovered in the evanescent wave formation region.     

All optical switching in henna thin film

The optical nonlinearity in henna (Lawson (2- hydroxyl-1,4 naphthoquinone) film was utilized to demonstrate all optical switching. The nonlinear absorption of the henna film was calculated by measuring the transmission of the laser beam (λ = 488 nm) as a function of incident light intensities. The observed nonlinear absorption is attributed to a two-photon absorption process. The pump and probe technique was used to demonstrate all optical switching. The switching characteristics can be utilized to generate all-optical logic gates such as simple inverter switches (NOT) NOR, AND NAND logic functions.     

Ultrashort optical pulse in a thin film of a topological insulator

We consider the propagation of ultrashort optical pulses in a thin film of a topological insulator within the framework of an effective long-wave Hamiltonian for low-temperature media. The electromagnetic field is taken as classical Maxwellian. We reveal the dependence on the maximum amplitude of ultrashort optical pulses.     

Optical behaviour of melting for a thin metal film

Reflectance measurements have been performed for gallium films at normal incidence (from 0.3 to 0.9 μm) in terms of temperature (from -20°C to + 40°C). The basic results are: (i) a drastic change in reflectance when melting occurs (about 20% at 0.6 μm), and (ii) a shift in the temperature of the solid-liquid transition with the thickness of the film which only takes place on and after the second melting (about 7°C for a film 250A?thick).     

Cerium dioxide thin film optical waveguides

Cerium dioxide thin film optical waveguides were fabricated by an RF magnetron sputtering process. The films were deposited on glass substrates and on silicon dioxide layers grown on silicon substrates. Optical loss measurements for the fabricated waveguides are reported. It is seen that the volume losses in the films were fairly high compared with the surface losses.     

Superresolution optical disk with a thermoreversible organic thin film

Recording and retrieving small marks far beyond the optical diffraction limit in a high-speed rotating phase-change optical disk have been investigated by use of a thermoreversible organic thin film as a superresolution mask layer. The organic thin film exhibited significant thermoreversibility and rapid response on laser irradiation. Recorded marks as small as 120 nm in length could be detected by a dynamic disk tester with a laser wavelength of 635 nm and a numerical aperture of 0.6.     

Four-layer metal-clad thin film optical waveguides

An investigation of the low order modes supported by an asymmetrical four-layered metal-clad optical waveguide is presented showing the attenuation characteristics and the field profiles. The attenuation and phase constants are examined as functions of both the thickness and refractive index of the buffer layer as well as the mode order. The results for small and large buffer layer thicknesses are discussed in terms of the modes supported by simpler asymmetrical three-layered metal-clad and dielectric-clad waveguides respectively. It is shown that the coupling of the TM polarized modes to the lossy surface plasma wave depends upon the buffer layer thickness, the refractive indices of the buffer layer and dielectric cladding and the mode order. This coupling is very dependent upon the mode order with the TM₀ mode exhibiting far weaker coupling than the higher order TM modes. Methods of controlling the amount of coupling and hence the attenuation of the TM modes are discussed.This work was performed while the author was with the Department of Electrical Engineering, University of Queensland, Brisbane, Australia, 4067.     

Nonlinear optical properties of a self-organized dye thin film

A self-organized thin film of a cyanine dye is fabricated by the spin-coating technique and is characterized by ultraviolet-visible spectroscopy, infrared (IR) spectroscopy, small-angle X-ray diffraction, ellipsometer,and atomic force microscopy (AFM). The nonlinear optical properties of the thin films are investigated by degenerate four wave mixing (DFWM) technique. The cyanine dye thin film sample exhibits high optical nonlinearities (χ(3) = 2.55 × 10-12 esu), and the mechanism is analyzed by the exciton coupling theory.     

Double nanohole apex-enhanced transmission in metal films

We first present experimental results of enhanced transmission through nanofabricated double-hole arrays in a gold film. An increase in the transmission is observed when the holes are overlapping to produce two apexes, with the transmission more than doubling when the apexes are nearly touching. When the holes are non-overlapping, the transmission maximum drops. The measured spectra through these arrays showed a red-shift in the peak transmission wavelength around 770 nm of nearly 30 nm. These experimental results agree well with our finite-difference time-domain simulations of the double-hole arrays. PACS 78.66.Bz; 42.79.Ag; 42.79.Dj