We present the results of an experimental investigation of the nonlinear optical properties of boric-acid glass doped with the organic dye fluorescein. This material has a very large third-order nonlinear optical susceptibility of approximately 1 esu, which is shown to be electronic and not thermal in origin. Measurements of the tensor nature of the nonlinear susceptibility are presented.
Lasing mechanisms for a laser resonator with cholesteric liquid crystal end mirrors were investigated. The effective radius of curvature of a cholesteric liquid crystal mirror was measured. The slope efficiency of a CLC-dielectric resonator was measured and compared with a flat-flat dielectric resonator with or without a pinhole for a Gaussian output.
We present a detailed theory and experimental study of infrared optical wave mixing based on thermal nonlinearity in nematic liquid crystal films. Because of the longer wavelength of infrared laser, lower scattering loss, transparency and other unique physical characteristics, very efficient degenerate optical wave mixing effects can be realized in nematic liquid crystal films. Applications to fairly fast (submillisecond) phase conjugations, beam and image amplification and self-pumped phase conjugation are also discussed.
The sensitivity function ▵R of WORM media often is a function of the incident energy (E) and pulsewidth (t), as well as incident power (P), of the write laser. A unified theory is developed to include all variables. It models the sensitivity function as ▵R (E,P,t) = AR (Y,t) [1 - X at (Y,t)/X], where X is the dominant and Y the secondary variable which determines media performance. ▵R(Y,t) is the saturation and X at(Y t) is the threshold behavior. The theory is applied to five distinct types of organic,T 'inorganic, and textured WORM media. The results are discussed and recommendations for test planning are made.
Electra-optic shutters that operate at a kilohertz rate have been demonstrated with nematic liquid crystals operated in the surface-mode or π-cell configuration. This principle has been employed to fabricate an NLC photoaddressed spatial light modulator that is faster than twisted-nematic devices.
The understanding of fracture in solid state lasers is reviewed, with an emphasis on fracture of high average power thin slabs. Methods for characterizing strength in the context of materials selection and device implementation are discussed. Progress in slab strengthening is analyzed; aggressive optical fabrication research (to give low damage surfaces), coupled with the implementation of existing schemes for placing the slab surfaces in compression, are recommended to reduce the problem of slab fracture.
A total internal reflection (TIR) spatial light modulator (SLM) employing the organic electrooptic crystal 2-methyl-4-nitroaniline (MNA) is discussed. The design configurations and performance characteristics are presented and compared with devices using inorganic electrooptic crystals such as LiNb03. It is estimated that the diffraction efficiency of a TIR SLM using MNA is enhanced by a factor of more than six compared with that using LiNb03, and, correspondingly, the driving voltage of the very large scale integration (VLIC) circuit is reduced approximately by a factor of two and half.
Polydiacetylene crystals with different kinds of side chains are formed and show two characteristic nonlinear-optical responses: the photo-induced structure change and the very large third-order optical susceptibility. The former property may be used as optical memory and the latter as the optical information processor. These two aspects of polydiacetylene are discussed in this paper.
The development of organic nonlinear optical materials requires the accurate measurement of its nonlinear optical and electrooptical properties. These measurements provide a guide to the synthesis and fabrication of new nonlinear organic materials with improved properties. A new technique for the electrooptical characterization of thin polymeric films is presented. This technique is used to measure the linear electrooptical Pockels effect in poled MNA/PMMA guest host glassy polymers. These results are compared to x(2) values derived from second harmonic generation studies. D. C. Kerr effect results are reported for a novel sol gel glass/PMMA composite material containing MNA. These results probe the relative mobility of MNA in PMMA at room temperature and elevated temperatures. x(3) values of several organic liquids are also measured by third harmonic generation studies in air. These values are compared with those derived from measurements in vacuum and good agreement is found between the two techniques.
The electro-optic response of nonlinear supermolecular arrays of organic dyes, prepared by the Langmuir-Blodgett (LB) technique is measured by an attenuated total reflection (ATR) method. The field induced dielectric constant changes in the films modify the coupling conditions for the excitation of a silver surface plasmon mode and produces a differential reflectivity in the region of the ATR minimum. The magnitude of the response is measured for film thicknesses corresponding to 1 through to 13 monomolecular LB layers. An anomalous dependence is seen. The anomaly occurs at a film thickness which segregates two thickness regimes for which the differential responses are qualitatively dissimilar. Structural re-organisations in the thin film regime may be responsible.
The categorization of existing polydiacetylene structures according to the nature of the polymer side-chain interactions is presented. Opportunities for generating new diacetylene molecular architectures based on creating mesogenic side-chains then becomes evident. Carrying through on this concept, the synthesis of four new symmetric diacetylene monomers based on the N-benzylideneaniline and cyanobiphenyl mesogens is reported. 1,6- Bis[N-(4-oxybenzylidene) 4-octylaniline] 2,4-hexadiyne(1-0BOA) contains a methylene oxide spacer between the mesogen and the diacetylene core and shows smectic liquid crystalline textures over a broad temperature range. Monomers containing a tetrametylene-oxide spacer do not show liquid crystallinity as monomers but are intended to result in liquid crystalline polymer.
The large nonresonant third order optical nonlinearities and fast response times of conjugated polymers make them attractive materials for nonlinear optics. The X(3) spectrum of polyacetylene and polydiacetylenes show similar structure, with magnitudes that agree with calculations of X(3) for the infinite polyene, as well as from the extrapolation of the calculated hyperpolarizabilities of finite polyenes. Of the conjugated polymers, the polydiacetylenes offer the best combination of physical properties since they can be obtained as large single crystals, thin crystalline films, Langmuir-Blodgett multilayers or as spun thin films. Unfortunately, all the conjugated polymers show some sensitivity to oxygen, though single crystals of polydiacetylenes are robust.
The introduction of advanced optical materials into communication technology facilitates increased data trans-mission speed, increased bandwidth, intrinsic low crosstalk and high security in multiplexed systems, and simplified implementation of parallel processing. Prototype and first-generation optical communication, information storage and information processing systems have been developed from hybrid electro-optical or all-optical effects in inorganic crystals and semiconductors. Organic and polymer nonlinear optical materials may have processing or performance ad-vantages in the next generation of optical information systems design, but research is needed to define the materials of interest and development will be necessary to incorporate these new materials into practical active elements. This paper is an overview of 3M's program for development of nonlinear optical materials.
A single molecular layer is generally sufficient to produce observable optical second harmonic generation (SHG). Furthermore, the selection rules governing this process make the SHG from a single monolayer often stronger than that from the medium supporting the monolayer. We have studied SHG from various Langmuir-type monolayers (i.e. monolayers spread on a water surface) in the following contexts: (1) Study of chemical reactions (e.g. polymerization) and two-dimensional phase transitions in molecular monolayers on water. (2) Development of a new technique to evaluate optical nonlinear coefficients of organic molecules, and their relationship to the molecular structure.
Highly oriented dye-containing polymer films are a promising class of nonlinear optical materials. We have prepared a poly(epicholorohydrin) derivative suitable for fabrication of noncentrosymmetric Langmuir-Blodgett (L/B) multilayer films. The synthesis, L/B deposition, and second harmonic generation measurements of these polymer films are reported.
A formal relation between molecular polarization and macroscopic nonlinear dielectric susceptibilities is derived. The importance of local field effects is reiterated. Application to crystalline and random media are discussed. To test validity of averaging procedures and semiempirical local-field models some optical third-harmonic generation experiments in binary solutions are described.
The convenient method for the short-time measurements using temporally incoherent light instead of short pulses was applied to electronic- and vibrational-dephasing-time measurement. Electronic dephasing in a polydiacetylene film and vibrational dephasing in dimethylsulfoxide liquid were observed with femtosecond time resolution.
Optical bistability has been observed in highly concentrated fluorescein dye solutions and in thin (-1 pm) doped polymeric films. At concentrations larger than 10-5 mole/k dye dimers are formed. For fluorescein dye, the dimer-monomer equilibrium constant is 10 -5 mole/ℓ so that most of the dye species are in the dimer form. At 480 nm the dimer absorption cross section is 10-18 cm2/molecule, while that for the dye monomer molecule is 7.6 x 10-17 cm2/molecule. Upon laser excitation dimers dissociate to form monomers thus providing a highly nonlinear laser induced absorption. This high nonlinear absorption coefficient can be utilized for optically bistable response of the dye system. Optical bistability was observed by placing dye solutions or dye thin films inside a Fabry-Perot resonator and exciting it with 480 nm dye laser pulses of 10 ns duration. The effect is more pronounced in 10-4 mole/ℓ fluorescein than in 10-6 mole/k fluorescein in which dimer formation is not that efficient.
Organic and polymeric materials have many useful features for thin-film electro-optic devices. These include low dielectric constants, moderate-to-large electro-optic coefficients, and low optical loss. This paper presents a review of the useful features of organic materials for device applications, summarizes the current optical response levels of some organic materials, and describes the performance of several device prototypes fabricated from poled organic films.
Optical power limiting behavior is demonstrated in several nonlinear optical polymers and organic model compounds that exhibit third-order optical nonlinearities. A remarkably sharp intensity-limiting behavior was observed in nonlinear transmission measure-ments of output versus input intensities at 1064 nm laser light without an aperture. The soluble novel organic polymers were found to exhibit both absorptive and refractive nonlinear optical effects that were evidenced by nonlinear absorption and temporal pulse steepening measurements. Nonlinear absorption coefficient (α2) and nonlinear index of refraction (n2) as high as 10 -7 cm/W and 10 -11 cm respectively were obtained at 1064 nm using a nanosecond Q-switched Nd:YAG laser. The observed nonlinearities decreased when measured with a 35 picosecond mode-lock laser. However, since the observed nonlinearities were independent of the energy density of the laser irradiation, it is suggested that the nonlinear mechanism is not thermal in origin. Solutions and solid films of the organic materials were studied. Intensity-limiting thresholds as low as 10 MW/cm2 and laser damage threshold greater than 10 GW/cm2 were obtained. It is suggested that nonlinear optical polymers hold promise for applications in passive optical limiting and regulating devices.
A particularly useful format for organic non-linear optical materials is that of a planar or stripe waveguide so that the materials can be utilised in integrated optical devices. The materials then have requirements placed upon them in addition to the need for high x2 or x3 coefficients: they must also be depositable in films of well controlled thickness and low scatter to enable low loss waveguiding to be performed over a sufficient distance to achieve non-linear interactions. Three approaches to achieving this in polymeric systems are described: 1. Non-linear dopant/film forming polymer/solvent systems where high levels of dopant can be achieved without phase separation in solvent cast, spun polymer films. 2. Solvent assisted indiffusion of non-linear dopant molecules into a polymer matrix material to produce slab or strip waveguides. 3. Deposition of novel non-linear optical polymers using the Langmuir Blodgett technique. Multilayer films have been built up to a sufficient thickness to achieve low loss waveguiding. For each of these approaches the choice of non-linear and/or polymer material will be discussed together with a description of the fabrication technique and optical properties of the finished structure. The applicability and suitability of these approaches to the fabrication of non-linear optical devices will be compared.
We are searching for new second and third harmonic generators among the salts of organic acids and bases. We discuss the relevant properties of crystals from this group of compounds, including their nonlinear and phasematching characteristics, linear absorption, damage threshold and crystal growth. In addition, we summarize what is known concerning other nonlinear optical properties of these crystals, such as two-photon absorption, nonlinear refractive index, and stimulated Raman thresholds. A preliminary assessment is made of the potential of these materials for use in future high power, large aperture lasers such as those used for inertial confinement fusion experiments.