Peter Guenter

Photorefractive gratings in the organic crystal 2-cyclooctylamino-5-nitropyridine doped with 7,7,8,8-tetracyanoquinodimethane

Single crystals of the electro-optic compound 2-cyclo-octylamino-5-nitropyridine (COANP) doped with small amounts of 7,7,8,8-tetracyanoquinodimethane (TCNQ) have been shown to be the first organic material exhibiting the photorefractive effect. Measurements of light induced gratings and beam coupling proved that the electro-optic response originates from photocarrier generation, charge separation, and the electro-optic effect driven by the space charge field.

Electro-optical and nonlinear-optical materials

Abstract This paper presents a review of electro-optical and nonlinear-optical crystals. Materials properties relevant for electro-optic modulator-, display- and storage applications and nonlinear-optical applications such as optical frequency doubling, optical parametric oscillation and optical sum- and difference frequency generation are discussed. Ferroelectrics as well as other piezoelectric dielectrics and semiconductors, with light transmission ranges extending from 180 nm up to 25 μm, have been included in this review.

KNbO 3 crystals for photorefractive applications

Characterization and optimization of KNbO 3 crystals for photorefractive applications over an extended spectral range is described. Intrinsic properties are used to describe the refractive index response to space-charge field gratings. Extrinsic properties that are important for the photorefractive effect, such as absorption, photoconductivity, charge transport, and trapping, are discussed. Some results on the extended IR response of crystals doped with Fe, Ni, Cu, Ce, Mn, and Co are presented. Post growth annealing at temperatures of 400 to 900°C in a controlled atmosphere is shown to modify the charge-transport parameters, therefore also modifying the response time of photoinduced refractive index changes.

Modified polyimide side-chain polymers with high glass transition temperatures for nonlinear optical applications

Novel modified polyimide polymers with nonlinear optical chromophores as pendent side groups show high glass transition temperatures and large nonlinear optical coefficients up to d33 equals 78 pm/V at (lambda) equals 1313 nm (electro-optic coefficient r33 equals 18 pm/V). Due to the high glass transition temperatures of up to 190

All-optical associative memory using photorefractive crystals and a saturable absorber

DEGC an excellent long term stability of the nonlinearity results. Extrapolation from measurements at elevated temperatures predict long term stabilities of the nonlinearity in excess of tens of years at 80

Second-harmonic generation with Ga1-xAlx as lasers and KNbO3 crystals

DEGC and hundreds to thousands of years at room temperature. The structural (molecular weight, glass transition temperature) and optical (refractive index, nonlinearity) properties of these polyimides can easily be varied which allows to taylor active layer and buffer layer materials.

Electrical properties of organic light-emitting diodes (OLEDs) studied by impedance spectroscopy in ultra-high vacuum

We report on the investigation of a new configuration of an all-optical associative memory. The images to be recalled associatively are stored in a LiNbO 3 crystal via angular multiplexing. Thresholding of the reconstructed reference beams during associative readout is achieved by using a saturable absorber with an intensity-tunable threshold. We demonstrate associative readout and error correction for 10 strongly overlapping black-and-white images. Associative recall and full reconstruction is performed when only 1/500 of the image stored is entered.

Molecular crystals for nonlinear optical applications

Abstract Possible materials for second-harmonic generation from pulsed Ga1-xAlxAs injection lasers operating at room temperature will be discussed. It is shown that KNbO3 fullfills all the requirements for this application ideally. Non-critical 90° phase matching in KNbO3 at room temperature is possible at λpm=860 nm for the nonlinear optical coefficient d32. Up to 0.35 mW harmonic power was obtained with a pulsed fundamental power of 785 mW from Ga1-xAlxAs lasers emitting near 860 nm with a KNbO3 crystal 5.74 mm long.

Electro-optic effects in organic single crystals

Alq3-based organic light emitting diodes (OLEDs) were prepared by molecular beam deposition in Ultra-High Vacuum (UHV) and their electrical properties were studied by impedance spectroscopy before they were exposed to any impurity gases. To characterize the fundamental injection processes, we studied the simplest OLED structure, consisting of a single layer of Alq3 between an ITO anode and a Mg cathode. In UHV, and below the threshold voltage for luminescent, instabilities in the frequency dependence of the resistivity, as well as in the current vs. voltage characteristics, are observed, which could be related to inhomogeneous contacting at the electrodes. When the same experiment is performed in air, both kinds of instabilities disappear, which demonstrates that exposure to atmospheric gas plays a role in stabilizing the contact and injection properties in the devices. Additionally, the impedance spectrum in air below the threshold voltage for luminescent shows an additional feature that hints to two different regions in the Alq3 layer, which we assign to the effect of Mg atoms which diffused into the Alq3 layer during deposition.

Waveguiding and nonlinear optics in 2-docosylamino-5-nitropyridine Langmuir-Blodgett films

We give an overview of the current status of research in the field of molecular crystals with respect to frequency-conversion, electro-optic modulation, and photorefractive effects. Applications of organic materials for nonlinear optics will depend on the development of waveguide devices and bulk crystals. Up to now the most advanced integrated optical organic devices use polymers. Thin crystalline films would also be very attractive if suitable techniques for high quality film deposition would become available. Organic molecular beam epitaxy offers new possibilities for fabricating low loss waveguides based on crystalline materials.