Ch. Bosshard

Organic Nonlinear Optical Materials

Introduction. Organic Electro-optic Compounds. Nonlinear Optics and Electro-optics. Crystal Growth of Organic Materials. Langmuir-Bloddgett Films. Electro-optic and Nonlinear Optical Polymers. Experimental Methods. Nonlinear Optical and Electro-optic Properties of Organic Compounds. Electro-optics and Nonlinear Optics in Waveguides. Photorefractive Effects in Organic Materials. References.

Electro‐optic properties of the organic salt 4‐N,N‐dimethylamino‐4′‐N′‐methyl‐stilbazolium tosylate

We show that the organic salt 4‐N,N‐dimethylamino‐4′‐N′‐methyl‐stilbazolium tosylate (DAST) is a very interesting material for electro‐optic applications in the near infrared. The electro‐optic coefficients, namely r111, r221, r331, r113, r223, and r333, were determined in the spectral range of 700 up to 1535 nm using optical samples cut from large high quality bulk crystals. DAST combines large electro‐optic coefficients, e.g., r111=77±8 pm/V at λ=800 nm and r111=47±8 pm/V at λ=1535 nm, with low dielectric constants, e.g., e1=5.2±0.4. This combination leads to large polarization‐optical coefficients.

PARAMETRIC INTERACTIONS IN THE ORGANIC SALT 4-N, N-DIMETHYLAMINO-4'-N'-METHYL-STILBAZOLIUM TOSYLATE AT TELECOMMUNICATION WAVELENGTHS

We show that the organic salt 4-N,N-dimethylamino-4′-N′-methyl-stilbazolium tosylate, originally developed for electro-optic applications, is also a very interesting material for phase-matched parametric interactions such as frequency-doubling and optic parametric oscillation in the near infrared. These favorable properties are due to the large off-diagonal element d26 which gives measured effective phase-matchable nonlinear optical coefficients of deff=31±5 and 15±3 pm/V at the telecommunication wavelengths of λ=1313 and 1535 nm, respectively.

2‐cyclooctylamino‐5‐nitropyridine, a new nonlinear optical crystal with orthorhombic symmetry

A new nonlinear optical crystal 2‐cyclooctylamino‐5‐nitropyridine (COANP) with point group symmetry mm2 has been grown by a temperature difference solution growth technique. Its linear and nonlinear optical properties have been investigated. The refractive indices na =1.702, nb =1.847, and nc =1.681 (λ=550 nm) and the nonlinear optical susceptibilities d31 and d33 (λω =1.06 μm) have been determined. Type I phase matching for Nd:YAG lasers (λ=1.06 μm) has been demonstrated for the configuration using a combination of d31 and d32 by angle tuning. A peak efficiency η=P2ω/Pω =3.6% has been observed with a 0.90‐mm‐thick crystal and a fundamental power Pω =560 W.

Second-order polarizabilities of nitropyridine derivatives determined with electric-field-induced second-harmonic generation and a solvatochromic method : a comparative study

A comparison is made between the second‐order polarizabilities of nitropyridine derivatives determined with two different methods: electric‐field‐induced second‐harmonic generation (EFISH) and a solvatochromic method. Both techniques yield the same values within the experimental errors, showing that the main contribution of the microscopic nonlinearity arises from a single intramolecular charge‐transfer transition. Based on the quantum‐mechanical two‐level model, the solvatochromic method also yields important molecular parameters, such as transition and excited‐state dipole moments. The second‐order polarizabilities determined with the EFISH method are shown to follow the theoretical two‐level dispersion.

Large nonlinear phase modulation in quasi-phase-matched KTP waveguides as a result of cascaded second-order processes

Nonlinear spectral modulation and broadening have been observed in quasi-phase-matched KTP waveguides near 850 nm, indicative of self-phase modulation that is due to cascaded second-order processes. Numerical beam-propagation simulations indicate nonlinear peak phase shifts larger than π for 600 W of peak power in a 2.8-mm-long guide.

Electro-optic effects in molecular crystals

The electro-optic properties of 2-cyclooctylamino-5-nitropyridine and 2-(N-prolinol)-5-nitropyridine single crystals have been evaluated. The dependence of the electro-optic coefficients on the optical wavelength and the frequency of the applied electric field was determined. Enhancements of these coefficients near acoustic resonances were observed and are discussed in terms of elasto-optic contributions. We propose a simple expression for estimation of the limiting values of electro-optic and nonlinear-optical coefficients. In addition, the wavelength dependence of the electro-optic figure of merit for organic and inorganic materials is estimated.

Linear- and nonlinear-optical properties of 2-cyclooctylamino-5-nitropyridine

The linear- and nonlinear-optical properties of 2-cyclooctylamino-5-nitropyridine (COANP) have been investigated. The refractive indices exhibit strong dispersion and a high birefringence (0.15–0.3) in the visible. The three main refractive indices at λ = 550 nm are na = 1.700, nb = 1.845, and nc = 1.683. The calculations that were carried out show interesting critical (frequency doubling of the Nd:YAG laser at λ = 1064 nm) and noncritical [sum-frequency generation using 488-nm (argon) and 647-nm (krypton)] phase-matching properties. The nonlinear-optical susceptibilities d32 = (32 ± 16) pm/V and d33 = (13.7 ± 2) pm/V were determined. A one-dimensional charge-transfer model can be used to explain the anisotropy of the nonlinear-optical susceptibility tensor of COANP qualitatively.

Optical waveguiding and nonlinear optics in high quality 2‐docosylamino‐5‐nitropyridine Langmuir–Blodgett films

The linear and nonlinear optical properties of well‐ordered Y‐type Langmuir–Blodgett (LB) multilayers of 2‐docosylamino‐5‐nitropyridine (DCANP) have been investigated. The nonlinear optical susceptibilities have been determined for the wavelengths λ=1064 nm [d33=(7.8±1) pm/V, d31=(2.0±0.5) pm/V] and λ=1318 nm [d33=(5.6±1) pm/V]. In first waveguiding experiments carried out TE0 and TM0 modes propagating over more than 20 mm could be excited. Coupling experiments allowed the determination of the dispersion of the refractive index n3 (n632.8 nm3 =1.598). Guided wave attenuation coefficients as low as 12 dB/cm (at the wavelength λ=632.8 nm) are reported.

Optical and nonlinear optical properties of 4‐(N,N‐dimethylamino)‐3‐acetamidonitrobenzene single crystals

A method of growing high quality 4‐(N,N‐dimethylamino)‐3‐acetamidonitrobenzene (DAN) single crystals is presented. Crystal plates with dimensions of up to 10×5×2 mm3 were produced and optically characterized. The transparency region extends from 485 to 2270 nm. Large birefringence and strong dispersion of the refractive indices were measured allowing two branches of type I and two of type II phase‐matched second‐harmonic generation. From effective second‐order nonlinear optical susceptibilities measured along the branches all nonlinear susceptibilities were evaluated, the highest being d23 =(50±15) pm/V.