Nonlinear optical laser devices using GaSe

Tunable second-harmonic generation of CO₂ laser radiation and tunable upconversion of infrared radiation from CO₂-laser radiation in a GaSe crystal are demonstrated. The capability of low infrared-signal detection in this crystal is also explored and compared with the AgGaS₂ crystal.     

Nonlinear optical studies in semiconductor-doped glasses under femtosecond pulse excitation

Nonlinear optical studies in semiconductor-doped glasses (SDGs) are performed under femtosecond laser pulse excitation. Z-scan experiments with 800 nm wavelength pulses are used to excite SDG samples in the resonance and non-resonance regimes. Schott colour glass filter OG 515 shows stronger two-photon absorption than GG 420 and both the samples exhibit positive nonlinearity. However, in resonantly excited RG 850 the intensity-dependent Z-scan shows transition from saturable to reverse saturable absorption behaviour with the increase in intensity.     

Second-order nonlinear optical properties of poled coumaromethacrylate copolymers

Second-order nonlinear optical properties of newly designed and synthesized coumaromethacrylate side-chain polymers are reported. The optimum poling conditions were determined experimentally. The optimum poling temperature for these side-chain polymers is well above the glass transition temperature. The second harmonic coefficient of films poled by coronaonset at elevated temperature and the linear electro-optic coefficient of films poled by contact electrodes were measured. The stabilized value of the second harmonic coefficient, d ₃₃, at 1064nm fundamental wavelength was found to be 13 pm/V. The linear electro-optic coefficient, r ₃₃, exhibits strong dispersion ranging from 2 to 12pm/V in the wavelength range 477 to 1115 nm.     

Annealing Induced Aggregations and Sign Alterations of Nonlinear Absorption and Refraction of Dense Au Nanoparticles in TiO2 Films

Au-TiO2 dis-conductive composite films with Au atom concentrate as high as 82% are prepared by using reactive co-sputtering technique. The annealing effect on the nanostructures and optical nonlinearities of the composite films are investigated. A u nanoparticles aggregated to semi-continuum network structures during the annealing processes. As the annealing temperature increases from 25℃ to 400℃, the surface plasmon absorption band is shifted and its strength is increased, consequently, the nonlinear absorption coefficient β decreases from 5.6 × 10^4 cm/GW to -1.7 × 10^4 cm/GW, while the nonlinear refractive index ~ increases from -0.95 cm^2/GW to 1.3 cm^2/GW.     

Photoinduced refractive index changes and photoluminescence in semiconductor-doped glasses

Transient refractive index changes of Cd(S, Se)-glasses induced by 10 ns laser pulses at 532 nm are determined from time-resolved transmission measurements of a Fabry-Perot interferometer containing samples of the semiconductor glass. Comparison of the transient index measurements with time-resolved photoluminescence supports an electron-hole-plasma model and suggests that the relaxation mechanism is Auger recombination of the electrons and the holes.     

Three-photon absorption and its limitation of third-order nonlinear optical effects in rutile

Three-photon absorption and three-photon-induced excited-state absorption of rutile are studied by transmission measurements using picosecond pulses of a mode-locked Nd: glass laser. The nonlinear absorption limits efficient stimulated Raman scattering. It reduces the efficiency of two-photon absorption of a picosecond probe continuum. Three-photon absorption coefficients, excited-state absorption cross sections, a Raman gain factor, and two-photon absorption cross-section spectra are determined. The arrangementsEc andE c are considered.     

Nonlinear optical properties of orthorhombic barium formate and magnesium barium fluoride

The nonlinear optical susceptibility tensors of barium formate (point group 222) and magnesium barium fluoride (point group mm 2) have been determined by the method of Maker fringes on the basis of a more rigorous theoretical treatment of second-harmonic generation of electromagnetic waves in plane-parallel plates of optically biaxial crystals. The measurements have been carried out in comparison with the KDP standard at awavelength of 1.064 μm (Nd: YAG). Both crystals possess nonlinear coefficients smaller than KDP (d ₃₆); they are phase matchable; magnesium barium fluoride exhibits a noncritical phase matching at a fundamental wavelenght of 1.04 μm.     

Nonlinear optical properties of organic dye dimer-monomer systems

An analysis is provided for the discussion of nonlinear optical properties of aggregated dye systems. The intensity-dependent transmission of fluorescein solutions excited by nanosecond dye laser pulses is shown to fit a monomer-dimer equilibrium shifted towards monomer formation by excitation. The implications for spatial light modulation and other nonlinear optical applications are discussed.     

Real-time optical image differentiation by degenerate four-wave mixing

Simple methods for performing real-time first-order image differentiation and quasi-differentiation, using degenerate four-wave mixing with photorefractive crystals, are described. A comparison is made between the methods for realizing image differentiation and image edge enhancement.     

Nonlinear optical rectification in parabolic quantum dots in the presence of electric and magnetic fields

The optical rectification (OR) coefficient in a parabolic quantum dots (QDs) subject to applied electric and magnetic fields is theoretically investigated in the framework of the compact-density-matrix approach and an iterative method. The confined wave functions and energies of electrons in the QDs are calculated in the effective-mass approximation. Numerical results are presented for typical GaAs/AlGaAs parabolic QDs. These results show that the OR coefficient strongly depends on the radius of QDs and the magnitude of electric and magnetic fields. And the peak shifts to the aspect of high energy when considering the influence of electric and magnetic fields.     

Structural and optical properties of lithium borobismuthate glasses

Glasses with compositions 25Li₂O-(75−x)Bi₂O₃-x B₂O₃, with 0?x?30 mol%, have been prepared using the melt quenching technique. The density and the molar volume have been determined. IR spectroscopy is used as a structural probe of the nearest neighbor environment in the glass network. The optical transmittance and reflectance spectrum of the glasses have been recorded in the wavelength range 400-1100 nm. The values of the optical band gap E_g^opt for indirect transition and refractive index have been determined for 0?x?30 mol%. The average electronic polarizability of the oxide ion α_o²⁻ and the optical basicity have been estimated from the calculated values of the refractive indices. Variations in the different physical parameters such as the density, molar volume, optical band gap, refractive index, average electronic polarizability of the oxide ion and optical basicity with B₂O₃ content have been analyzed and discussed in terms of the changes in the glass structure.     

Nonlinear optical response of Ge nanocrystals in silica matrix with excitation of femtosecond pulses

We report an investigation of third-order optical nonlinearities in Ge nanocrystals (∼6 nm radius) embedded in silica matrix using the Z-scan and pump-probe techniques with femtosecond laser pulses at 780-nm wavelength. The nanocrystallite Ge samples were prepared using magnetron co-sputtering and post-thermal annealing at 800 °C. The nonlinear absorption coefficient and refractive index of the Ge nanocrystals were determined to be in the range from 1.8×10^-7 to 6.8×10^-7 cm/W and 1.5×10^-12 to 8.0×10^-12 cm²/W, respectively, which are proportional to the Ge atomic fraction in the matrix. Relaxation of the nonlinear response was found to have two characteristic time constants, 1.8 ps and 65 ps. The mechanisms responsible for the observed nonlinear response are discussed. Received: 21 August 2000 / Revised version: 17 January 2001 / Published online: 30 March 2001     

Nonlinear optical properties of a hydrogenic donor quantum dot

A investigation of the nonlinear optical properties of a hydrogenic donor in a disc-like parabolic quantum dot has been performed by using the matrix diagonalization method. The optical absorption coefficient between the ground (L=0) and the first excited state (L=1) have been examined based on the computed energies and wave functions. The results are presented as a function of the incident photon energy for the different values of the incident optical intensity and the confinement strength. We found the total optical absorption coefficient is strongly affected by the incident optical intensity and the confinement strength.     

The effect of the relative position of the bandgap with respect to laser wavelength on the behaviour of DFWM in semiconductor-doped glasses

Degenerated four-wave mixing (DFWM) was realised in five commercial semiconductor-doped glasses (Corning CS3–66, CS3–67, CS3–68, CS3–69, CS3–70). The reflectivity obtained for each glass seems very dependent on the energy excess (E=hv–E _g) and relatively independant on l, the product of the absorption coefficient () by the sample thickness (l). The decay time of the DFWM signal was measured for each glass. The relaxation was found to be different when the photon energy is under or over the gap.     

The optical kerr effect in small metal particles and metal colloids: The case of gold

We first consider theoretically the various mechanisms contributing to the Kerr nonlinearity in small gold particles. The major ones are the conduction electron intraband contribution, the saturation of direct interband transitions and the change in dielectric constant due to hot photoexcited electrons. We present experimental results obtained using optical phase conjugation in gold-doped glasses. By varying several parameters, we were able to ascertain the origin of the nonlinear response: the main contributions are the hotelectron and the interband contributions. All experimental results, including saturation behaviour, are fully understood.     

Nonlinear optical properties and photoinduced anisotropy of an azobenzene ionic liquid-crystalline polymer

The nonlinear optical properties and photoinduced anisotropy of an azobenzene ionic liquid-crystalline polymer were investigated. The single beam Z-scan measurement showed the polymer film possessed a value of nonlinear refractive index n₂ = −1.07 × 10⁻⁹ cm²/W under a picosecond 532 nm excitation. Photoinduced anisotropy in the polymer was studied through dichroism and photoinduced birefringence. A photoinduced birefringence value Δn ∼ 10⁻² was achieved in the polymer film. The mechanism for the nonlinear optical response and the physical process of photoinduced anisotropy in the polymer were discussed.     

Post-annealing effect upon optical properties of electron beam evaporated molybdenum oxide thin films

Molybdenum oxide (MoO₃) thin films were deposited by electron beam evaporation. The chemical composition, microstructure, optical and electrical properties of MoO₃ thin films depend on the annealing temperature and ambient atmosphere. X-ray diffraction (XRD) shows that crystalline MoO₃ films can be obtained at various post-annealing temperatures from 200 to 500 °C in N₂ and O₂. X-ray photoelectron spectroscopy (XPS) results reveal that the O-1s emission peak was shifted slightly toward lower binding energies as the annealing temperature in N₂ was increased. The oxygen vacancies and conductivity of MoO₃ film increased with the annealing temperature. However, when the MoO₃ films were annealed in an atmosphere of O₂, the optical transmission, the O/Mo ratio and the photon energy increased with the annealing temperature. The results differ from those for films annealed in a N₂ atmosphere.     

Annealing effect on the ultrafast dynamics of Ag nanoparticles embedded in soda-lime silicate glasses

Ag nanoparticles embedded in soda-lime silicate glasses were fabricated by the ion-exchange technique. Effects of thermal treatment on the optical nonlinearity and ultrafast dynamics of Ag nanoparticles were investigated by applying time-resolved optical Kerr effect and pump-probe techniques. The results indicate that thermal treatment is an efficient method to improve the nonlinear optical performance of this kind of material.     

Chemical-bond analysis of the nonlinear optical properties of the borate crystals LiB3O5, CsLiB6O10, and CsB3O5

The second-order nonlinear optical properties of practical borate crystals, LiB₃O₅, CsLiB₆O₁₀, and CsB₃O₅, which all contain the identical basic structural unit [the (B₃O₇)^5- group], have been quantitatively studied from the chemical-bond viewpoint. Differences in the nonlinear optical properties among these three borate crystals arise from the contributions of the different cations, i.e., the different interaction between the cation and the (B₃O₇)^5- anionic group. The chemical-bond method quantitatively expresses this important difference. At the same time, the current calculation also shows that the B₃O₇ group is a very important crystallographic frame in the crystalline borate solids; it offers different cations an excellent coordination environment. Received: 20 February 2001 / Accepted: 14 June 2001 / Published online: 30 August 2001