Purified deoxyribonucleic acid (DNA), derived from salmon milt and roe sacs, waste products of the Japanese fishing industry in Hokkaido, has been processed into a promising, optical waveguide quality, biopolymer material suitable for both passive and active optical and electro-optic applications. Intercalation of aromatic compounds into stacked layers within the double helix of DNA molecules has rendered active optical waveguide materials with excellent nonlinear optical properties.
A frequency-unshifted and backward stimulated scattering can be efficiently generated in one-photon-absorption free but two-photon absorbing materials. Using a number of novel two-photon absorbing dye solutions as the scattering media and nanosecond pulsed laser as the pump beams, a highly directional backward stimulated scattering at the exact pump wavelength can be readily observed once the pump intensity is higher than a certain threshold level. The spectral and spatial structures as well as the temporal behavior and optical phase-conjugation property of this new type of backward stimulated scattering have been experimentally studied. This stimulated scattering phenomenon can be explained by using a model of two-photon-excitation enhanced standing-wave Bragg grating initially formed by the strong forward pump beam and much weaker backward Rayleigh scattering beam; the partial reflection of the pump beam from this grating provides an positive feedback to the initial backward Rayleigh scattering beam without suffering linear attenuation influence. Comparing to other known stimulated (Raman, Brillouin, Rayleigh-wing, and Kerr) scattering effects, the stimulated Rayleigh-Bragg scattering exhibits the advantages of no frequency-shift, low pump threshold, and low spectral linewidth requirement.
Recent successes in developing two-photon absorption (2PA) materials and applications have now created significant interest in exploring three-photon absorption (3PA) based novel optical materials and new applications. 3PA-based techniques may exhibit two major advantages: (1) much longer IR wavelengths (1.2-1.7 μm) can be used, and (2) much better beam confinement (resolution) can be achieved owing to the cubic dependence of nonlinear absorption on the local intensity of the excitation IR light. We have demonstrated efficient three-photon excitation in a number of nonlinear organic materials developed at our Institute or in cooperation with other research groups. The 3PA capability of a given material can be estimated by measuring the 3PA coefficient (or cross-section) at a given excitation wavelength or as a function of the wavelength. The 3PA-active materials can be either highly fluorescent or non-fluorescent. Potential applications of novel and highly efficient three-photon absorbing materials include (i) three-photon pumped (3PP) and frequency upconverted lasing, (ii) 3PA-based optical power limiting and stabilization, (iii) 3PA-based bio-imaging via IR to visible conversion, and (iv) 3PA-associated 3D data storage and microfabrication. Some recent experimental results of 3PP lasing as well as 3PA-based power limiting are briefly presented.
Two-photon absorption (TPA), a molecular excitation process by the simultaneous absorption of two photons, has recently attracted growing interest in many photonic and optical applications because of the availability of chromophores that exhibit large, effective TPA cross-sections. Over the past 6-7 years, we have successfully synthesized a family of TPA molecules (designated as AFX) that possess large nonlinear optical properties, including unsymmetrical and multi-branched chromophores comprised of 'electron acceptor-aromatic bridge-electron donor’ structural motif. These chromophores are excitable with useful wavelengths around 800 nm and fluoresce in the 400-450 nm region. However, practical uses of these chromophores depend on developing functionalization chemistry pertinent to specific applications. We are particularly interested in incorporating these TPA active molecules into polymeric or low melting glassy materials that are amenable to easy processing and fabrication. Our recent results in this direction will be discussed in this paper.
Optical power limiting can be accomplished by a variety ofmaterials whose spectral and temporal utility is determined
by a number ofparameters. The most important determinant ofhow a particular material will perform is defmed by
the mechanism(s) by which optical power limiting is achieved. This paper discusses the use of complementary materials
to obtain the greatest spectral and temporal range. One new class of materials has strongly absorbing charge states
(cationic and dicationic) which make them highly desirable for consideration. Several materials are discussed along
with their optical characterization. These processes can be carried out in solutions containing various compounds
including electron acceptors. Other materials such as two photon absorbing materials exhibit optical power limiting with
shorter response times and/or over different spectral regions. Recent progress in the development and characterization
oftwo photon absorbing compounds is discussed with particular attention to how they can be used in a complementary
fashion with other compounds operating through other mechanisms to deliver broad optical power limiting responses.
In this paper, the theoretical and experimental studies of the orientational characteristics of electro-optic chromophore in a low glass transition temperature material are presented. The amplitude and the phase behaviors of the orientation have been discussed. The photorefractivity in a material PVK:TCP:APSS:C60 is experimentally studied.
A newly synthesized laser dye, trans-4-[P-(N-ethyl-N-hydroxyethylamino)styryl]- N-methylpyridinium tetraphenylborate (dye I), has high thermal- and photo-stability as well as strong two-photon-induced upconversion emission. Utilizing dye I doped bulk polymer rods, two-photo pumped frequency unconverted cavity lacing has been accomplished using a Q- switched Nd:YAG laser as the pump source. The upconversion lacing efficiency was 3.5%, and the cavity lacing lifetime, in terms of pulse numbers, was more than 4 by 104 pulses at 2 Hz repetition rate. By impregnating these dyes into a silica-gel:polymethylmethacrylate (PMMA) and Vycor-PMMA composite glasses, two-photon cavity lacing properties have also been studied.
Polyimides possess interesting nonlinear optical properties. The overall goal of our effort is to develop the requisite synthesis and processing techniques to produce polyimides with high (Chi) (3) and low absorptive losses. The target value for many applications is (Chi) (3)/(alpha) equals 10-7 esu-cm. The synthesis and characterization of both the linear and nonlinear optical properties of these materials and the requirements for their utilization in optical bistability is reported.