Growth and nonlinear optical properties of Zn-doped LiB3O5 crystals

Zn-doped LiB₃O₅ (LBO) single crystals with high quality were successfully grown from the Li₂O–MoO₃–ZnF₂ ternary system by the top-seeded solution growth method. The suitable region for LBO crystal growth was investigated by growth experiments, as well as viscosity and volatility measurements, which confirmed that the optimal molar ratio of Li₂O:MoO₃:ZnF₂ was 1:1.5:0.2. The second-harmonic generation efficiency of Zn-doped LBO crystal increased by 16% compared with that of the LBO crystals grown from the MoO₃ flux. The optical homogeneity was at 10⁻⁶ cm⁻¹. Optical absorption at the critical wavelengths of 1064 nm was measured to be 15 and 18 ppm cm⁻¹, respectively.     

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.     

Optical second harmonic generation in CsLiB6O10 nanocrystallites incorporated to the olygoether photopolymer matrices induced by acustical field

Optical second harmonic generation in CsLiB₆O₁₀ (CLBO) large-sized nanocrystallites (15–40 nm) incorporated into the olygoether photopolymer matrices has been found at liquid helium temperature (LHeT). The second harmonic generation (SHG) has been measured for the source wavelength of the YAG : Nd laser ( = 1.06 m). Increasing acoustical power (up to 18.1 W/cm²) and acoustical frequencies at 14 kHz give maximal values of the output SHG. The measured SHG ₂₂₂ tensor component was comparable with the one for the traditional nonlinear optical crystals such as KH₂PO₄, KTiOPO₄, LiNbO₃. With decreasing temperature below 28 K the acoustically induced SHG signal strongly increases. A correlation between the acoustically induced SHG and low-frequency Raman modes has been found. The maximal acoustically induced SHG has been observed for the nanocrystallite concentration about 3.1% (in weighting units) and the crystallite sizes lying within the 35–40 nm. The SHG tensor coefficients were higher than for the proper CLBO crystals at least on the 13%. Advantageous and drawbacks of the presented model are discussed. The theory of the observed phenomena is explained on the ground of ab initio band energy calculations with taking into account of anharmonic electron-phonon interactions.     

Efficient continuous-wave ultraviolet generation in LiB3O5 and RbD2AsO4

We have demonstrated two continuous-wave nonlinear processes: third-harmonic generation (THG) of 1064-nm radiation with a lithium triborate (LBO) crystal, and second-harmonic generation of 696-nm radiation in deuterated rubidium dihydrogen arsenate. With 34 mW of 1064-nm and 25 mW of 532-nm radiation incident upon the LBO crystal, as much as 60 nW of third-harmonic power has been produced. We present the characteristics that optimize the production of nonlinear power in this sum-frequency generation process. In the second experiment, 15 nW of radiation at 348 nm was produced with 9 mW of 696-nm incident radiation. Both processes will play an important role in the new generation of optical synthesis techniques.     

Large enhancement of second harmonic generation in highly cerium doped lead-phosphate glass

The influence of lead and cerium concentration on photoinduced second harmonic generation (SHG) in lead-phosphate glasses has been studied. It has been shown that SHG can be considerably enhanced by increasing of lead and cerium concentration. We also have found that cerium greatly extends the induced nonlinearity lifetime. Physical mechanism of the phenomenon is discussed.     

Relationship between surface plasmon and transmittance enhancement in indium-tin-oxide/Ag/indium-tin-oxide multilayer electrodes

The transmittance of indium-tin-oxide (ITO)/Ag/ITO multilayer electrodes under various annealing conditions was investigated. The surface morphology of the Ag layer was modified according to the annealing conditions. Depending on the surface formation of the Ag layer, the enhancement of the transmittance was differentiated into two types. Because of a change of the surface plasmon (SP) mode, connected Ag clusters with coverage of 60% resulted in transmittance enhancement over all visible wavelengths due to decreased absorption while those with coverage of 50% resulted in transmittance enhancement with a peak shift due to increased scattering by localized SP.     

Effect of electron beam irradiation on the electrical and optical properties of ITO/Ag/ITO and IZO/Ag/IZO films

We have investigated the effect of electron beam irradiation as well as insertion of a Ag layer on the electrical and optical properties of the ITO or IZO films. The results show that electron beam irradiation as well as inserting a very thin Ag layer can significantly reduce sheet resistance of the ITO/Ag/ITO and IZO/Ag/IZO films. The electron beam irradiation also increases light transmittance and optical band gap of the ITO/Ag/ITO multilayer films; meanwhile, it has not influence on the transmittance of the IZO/Ag/IZO films. These results can be explained by that In and Zn cation in IZO film have strong tendency to preserve their coordination with oxygen.     

Luminescence and second harmonic generation in Eu/Eu embedded B2O3: LiNbO3 non-linear glass-ceramics

Multifunctional europium doped Li₂O-Nb₂O₃-B₂O₂ glass has been prepared by melt-quench method. Through subsequent heat treatments glass has then been transformed into glass ceramics containing ferroelectric LiNbO₃ phase. The glass ceramics have shown enhanced Eu³⁺ emission compared to parent glass when excited by 266 nm radiation. The emission measurements of glass ceramics have also shown the presence of Eu²⁺ state along with Eu³⁺ and Eu²⁺ state was found to increase when glass was heated in inert atmosphere. Lifetime of the ⁵D₀ level of the Eu³⁺ has been measured and a significant increase is found in case of glass ceramic prepared around glass transition temperature. Glass ceramics have also shown good second harmonic generation (SHG) with pulsed 1064 nm laser excitation.     

Quasi-phase-matched second harmonic generation device in Mg-doped LiNbO3 and its application to high-density optical disk system

The resistance to photorefractive damage is investigated for several nonlinear crystals. A quasi-phase-matched (QPM) second harmonic generation (SHG) waveguide device is fabricated in 5 mol% Mg-doped LiNbO₃ which has high resistance to optical damage. The SHG blue laser of the QPM-SHG waveguide device and a tunable distributed Bragg reflector (DBR) laser diode is demonstrated, wherein output stability of continuous blue light is measured. The SHG blue laser, using the QPM-SHG waveguide device with broadened flat matching response, shows good modulation characteristics. The pulsed peak power of 23 mW with rectangular modulated waveform is generated. The SHG blue laser is installed to an optical head, and good recording and readout characteristics are demonstrated. Moreover, butt-coupled SHG blue laser is examined to gain a miniature module with volume of 0·8 cc.     

Probing and modeling of carrier motion in organic devices by optical second harmonic generation

We here report a novel optical second harmonic generation (SHG) measurement that allows an electric field formed in organic solid to be probed. We examined the SHG intensity profile that changes depending on a space charge field caused by carrier injection. Experiments making use of time-resolved SHG technique has revealed dynamic changes of SHG intensity profiles arising from pentacene, and that carrier transport in OFET was diffusion-like. Calculations using drift-diffusion equation well accounted for the visualized carrier motion probed by time-resolved SHG. That is, interface charge propagation process dominates the carrier transport, which is regulated by applied gate-source voltage.     

Improved electrical and optical properties of ITO/Ag/ITO films by using electron beam irradiation and their application to ultraviolet light-emitting diode as highly transparent p-type electrodes

We have investigated the effect of insertion of a Ag layer in ITO film as well as electron beam irradiation to the multilayer films on the electrical and optical properties of the ITO-based multilayer deposited by magnetron sputtering method at room temperature. Inserting a very thin Ag layer between ITO layers resulted in a significant decrease in sheet resistance and increased the optical band gap of the ITO/Ag/ITO multilayer to 4.35 eV, followed by a high transparency of approximately 80% at a wavelength of 375 nm. We have also fabricated ultraviolet light-emitting diodes (LED) by using the ITO/Ag/ITO p-type electrode with/without electron beam irradiation. The results show that the UV-LEDs having ITO/Ag/ITO p-electrode with electron beam irradiation produced 19% higher optical output power due to the low absorption of light in the p-type electrode.     

Nafion-coating of the electrodes improves the flow-stability of the Ag/SiO2/Ag2O electroosmotic pump

When a current or a voltage is applied across the ceramic membrane of the nongassing Ag/Ag(2)O-SiO(2)-Ag/Ag(2)O pump, protons produced in the anodic reaction 2Ag(s) + H(2)O → Ag(2)O(s) + 2H(+) + 2e(-) are driven to the cathode, where they are consumed by the reaction Ag(2)O(s) + H(2)O + 2e(-) → 2Ag(s) + 2 OH(-). The flow of water is induced by momentum transfer from the electric field-driven proton-sheet at the surface of the ceramic membrane. About 10(4) water molecules flowed per reacted electron. Because dissolved ions decrease the field at the membrane surface, the flow decreases upon increasing the ionic strength. For this reason Ag(+) ions introduced through the anodic reaction and by dissolution of Ag(2)O decrease the flow. Their accumulation is reduced by applying Nafion-films to the electrodes. The 20 μL min(-1) flow rate of 6 mm i.d. pumps with Nafion coated electrodes operate daily for 5 min at 1 V for 1 month, for 70 h when the pump is pulsed for 30 s every 30 min, and for 2 h when operating continuously.     

Influence of Ag thickness on electrical, optical and structural properties of nanocrystalline MoO3/Ag/ITO multilayer for optoelectronic applications

In this study, MoO₃/Ag/ITO/glass (MAI) nano-multilayer films were deposited by the thermal evaporation technique and then were annealed in air atmosphere at 200 °C for 1 h. The effects of Ag layer thickness on electrical, optical and structural properties of the MoO₃(45 nm)/Ag(5-20 nm)/ITO(45 nm)/glass nano-multilayer films were investigated. The sheet resistance decreased rapidly with increasing Ag thickness. Above a thickness of 10 nm, the sheet resistances became somewhat saturated to a value of 3(Ω/□). The highest transparency over the visible wavelength region of spectrum (85%) was obtained for 10 nm Ag layer thickness. Carrier mobility, carrier concentrations, transmittance and reflectance of the layers were measured. The allowed direct band-gap for an Ag thickness range 5-20 nm was estimated to be in the range 3.58-3.71 eV. The XRD pattern showed that the films were polycrystalline. X-ray diffraction has shown that Ag layer has a (111) predominant orientation when deposited. The figure of merit was calculated for MAI multilayer films. It has been found that the Ag layer thickness is a very important factor in controlling the electrical and optical properties of MAI multilayer films. The optimum thickness of the Ag layer for these films was determined. The results exhibit that the MAI transparent electrode is a good structure for use as the anode of optoelectronic devices.     

Experimental and theoretical studies of second harmonic generation for Bi2O2[NO3(OH)]

The structural characteristics and optical properties of bismuth nitrate Bi₂O₂[NO₃(OH)] (BINO) are investigated by experimental in combination with theoretical studies. The BINO crystal was obtained from the hydrothermal growth, and its UV–Vis absorption spectrum was measured. Second harmonic generation (SHG) experiments on powder sample show that BINO is a phase-matchable nonlinear optical crystal with a large powder SHG coefficient of 2.3 pm/V, which is confirmed by the first-principles calculations. Moreover, the structural origin of nonlinear optical effects in BINO is given. Our studies reveal that BINO is a promising SHG crystal in the visible and infrared spectral region.     

Structural and optical properties of ge nanocrystals embedded in Al2O3

Ge nanocrystals (NCs) embedded in aluminum oxide were grown by RF-magnetron sputtering. Raman, high resolution transmission electron microscopy (HRTEM), selected area diffraction (SAD), and X-ray diffraction (XRD) techniques confirmed good cristallinity of the NCs from samples annealed at 800 degrees C. The average NC size was estimated to be around 7 nm. Photoluminescence (PL) measurements show an emission related to the NCs. The temperature dependence of the PL confirms the confinement phenomenon in the Ge NCs.     

Raman spectroscopy study of the phase transformations of LiB3O5 and Li2B4O7 during heating and melting

The incongruent melting of LiB₃O₅ (LBO) single crystals and transformations of the boron-oxygen groups in glasses and melts with the compositions Li₂O · 2B₂O₃ and Li₂O · 3B₂O₃ have been studied by Raman spectroscopy. The vapor over superheated melts of these condensed lithium borates has been shown to contain [BO₂] radicals.     

Measurement of intensity of the second optical harmonic in heteroepitaxial cadmium-mercury telluride structures

Features of the generation of the second optical harmonic in the heterostructures HgCdTe/GaAs and CdTe/HgCdTe/GaAs manufactured by means of molecular-beam epitaxy are experimentally investigated for the first time. The dependences of the intensity of a nonlinearly optical signal on the direction of the pumping radiation polarization and the position of the laser beam on the study surfaces are measured for a pure monocrystalline substrate and for a sample with a deposited functional polycrystalline CdTe layer. Substantial differences between these dependences are discovered.     

Influence of the interaction between two Ag nanoparticles on optical properties of Ag/PGMEA nanocomposite materials

We report local electric field calculations in Ag/PGMEA nanocomposite materials using the dipole discrete approximation. We employ calculation and simulation to show that the nanoparticle radius and the interparticle distance could control and tune the surface plasmon resonances, which influence the extinction spectra and the near-field enhancement of Ag/PGMEA nanostructures. With decreasing interparticle distance, the near-field coupling between particles will induce the shift of surface plasmon resonance peak and improve the near-field intensity. With increasing radius (r), the resonance wavelength peak is red-shifted because of the interaction between two Ag nanoparticles. At 449 nm, the highest near-field enhancement factor obtained in the center of the gap was 30.5 for two interacting Ag nanoparticles of r = 11 nm with a gap of 5 nm.