Weiping Lin

Second‐harmonic generation of poled BaTiO3 thin films

Second‐harmonic generation of 1.064 μm incident light was measured on BaTiO3 thin films prepared by metalorganic chemical vapor deposition. Upon corona poling of the film, the second‐harmonic signal was significantly enhanced. The second‐order nonlinear optical susceptibility, d, of the poled film reaches ∼7.5 times that of the quartz. The enhanced second‐harmonic generation shows a very slow decay at room temperature.

NONLINEAR OPTICAL PROPERTIES OF TEXTURED STRONTIUM BARIUM NIOBATE THIN FILMS PREPARED BY METALORGANIC CHEMICAL VAPOR DEPOSITION

Highly textured strontium barium niobate thin films were deposited in situ by low pressure metalorganic chemical vapor deposition. [001]‐oriented strontium barium niobate films on single crystal (100) magnesium oxide substrates were obtained at a growth temperature of 800 °C. Second‐harmonic generation of 1.064 μm incident light was measured on the thin films. The nonlinear optical susceptibility of the films was as high as 8.7 times that of quartz (∼3.0 pm/V), which is comparable to the bulk value.

Epitaxial potassium niobate thin films prepared by metalorganic chemical vapor deposition

Epitaxial potassium niobate thin films were deposited in situ by low pressure metalorganic chemical vapor deposition (MOCVD) at a growth temperature of 800 °C using niobium pentaethoxide and potassium tert‐butoxide as volatile metalorganic precursors. Growth on single crystal (100) lanthanum aluminate substrates produced [110]‐oriented potassium niobate films. The films have a smooth, featureless morphology. Atomic force microscopy of the MOCVD‐derived films surface indicates a root‐mean‐square roughness of less than 2 nm. Second‐harmonic generation of 1.064 μm incident light is observed from the potassium niobate thin films, and the effective second order nonlinear susceptibility d of the as‐deposited film is as high as 13 pm/V.

Second harmonic generation in hexagonal silicon carbide

We report optical second harmonic generation measurements in single crystal α‐SiC of polytype 6H. The angular dependence of second harmonic intensity was consistent with two independent nonvanishing second order susceptibility components, as expected for a crystal with hexagonal symmetry. For the fundamental wavelength of 1.064 μm the magnitudes of the two components were determined to be χzzz(2)=±1.2×10−7 and χzxx(2)=∓1.2×10−8 esu. The corresponding linear electro‐optic coefficient computed from this value is rzzz=±100 pm/V. The wavelength dependence of the nonlinear susceptibility was examined for second harmonic wavelengths between the bandgap (400 nm) and the red (700 nm), and was found to be relatively uniform over this region. The refractory nature of this compound and its large nonlinear optical coefficients make it an attractive candidate for high power nonlinear optical waveguide applications.

ULTRAVIOLET SECOND HARMONIC GENERATION IN RADIO-FREQUENCY SPUTTER-DEPOSITED ALUMINUM NITRIDE THIN FILMS

Optical second harmonic generation in radio‐frequency sputter‐deposited AlN thin films has been studied for harmonic wavelengths from ultraviolet to near infrared. The effective second‐order nonlinearity χ(2)(ω) was determined to have a nonresonant background value of ∼5×10−9 esu for second harmonic wavelengths longer than 400 nm, and it increases dramatically as the second harmonic frequency approaches the bandgap of 6.2 eV. This is likely due to resonance of the second harmonic frequency with the critical point transition associated with the direct bandgap of AlN.

Second order optical nonlinearities of radio frequency sputter‐deposited AlN thin films

Polarized second harmonic generation measurements were performed on AlN films deposited on (100) sapphire substrates by the reactive rf sputtering technique. The bulk effective second order nonlinearity observed in these films is typically about 6×10−9 esu at 1.06 μm, several times larger than that of quartz or KTP. The tensorial properties of the nonlinearity are consistent with the crystal symmetry of AlN and the microcrystallinity of these films.

Electronic beam induced poling of BaTiO3 thin films

The effect of electron beam irradiation on second harmonic generation of BaTiO3 thin films was studied. Enhanced second harmonic intensity was measured from BaTiO3 thin films irradiated by electron beams of 10, 15, and 25 keV using a scanning electron microscope. The enhancement of the second harmonic generations is attributed to the electron beam‐induced poling of the film. The effectiveness of the electron beam irradiation on second harmonic generation enhancement is comparable to that of the corona poling of the film at room temperature. This electron beam induced poling technique offers a promising method for nonlinear optical device fabrication.

Self-assembled chromophoric thin film NLO materials. Effect of coupling agent surface functionalization and ion exchange processes on second harmonic generation characteristics

Abstract A systematic study of the reaction of 1-chloromethyl-4-(2-trichlorosilylethyl)-benzene (coupling agent) with the surface SiOH groups of glass for times from 15 min to 48 h, followed by stilbazole chromophore precursor deposition/quaternization, is reported. Second harmonic generation characteristics of these thin film materials indicate that a 15 min coupling agent reaction attains approximately 65% of full surface coverage (based on χ zzz (2) ) of benzylic chloride moieties, but that 24 h is the optimal time for maximum coverage. The surface-anchored chromophoric chloride salts in such materials undergo facile ion exchange with iodide, p -aminobenzenesulphonate, and ethyl orange, leading to enhancements in χ zzz (2) of up to 50%.

Knowledge base for the design of high-performance second-order NLO materials: architecture-relaxation correlations in new crosslinked poled polymer systems

Two complementary approached to the construction of poled, crosslinked second-order polymeric NLO materials are discussed. In the first, poly(p-hydroxystyrene) is functionalized with a nitroaniline chromophore having a protectable hydroxyl group for hydrogen bonding or epoxy crosslinking. Chromophore immobilization is most effective when crosslinks can be made directly at the chromophore substituent and when multifunctional crosslinking agents are employed. The second approach shows that matrices prepared from an aryldiamine chromophore and a bismaleimide co-monomer can achieve Tg values approaching + 240

Observation of an optical-modulation effect on second harmonic generation in C60 thin films

DEGC and exceptional SHG temporal stability.