Nonlinear optical phenomenon

This term is responsible for the generation of frequency-doubled light. A prerequisite is that the crystal has a non-central symmetric structure. Using symmetry arguments, it can be shown that for a material with a centre of symmetry all even coefficients x etc. must vanish. Since is always small it is necessary for c q be sufficiently high. With pulsed lasers electric field strengths of a sufficient magnitude ( 10 V/cm) can easily be 

By using an intracavity frequency-doubling crystal or an external enhancement cavity [8.71,72] continuous frequency doubling and mixing can also be achieved for cw dye laser radiation. Powers of several mW can then be achieved (Fig. 8.28). 

It can be seen that apart from the doubled frequencies, sum and difference frequencies are obtained. The phase matching is chosen to strongly enhance 

The Optical Parametric Oscillator (OPO) process should also be mentioned. Here a nonlinear crystal in a cavity is used to generate two new frequencies (oji and 0J2) out of a single one (a ) that is used to pump the crystal. Energy conservation requires Ui- U 2 = ct . The frequency division between the two new waves (the signal and the idler) is chosen by the phase matching condition. The parametric process can also be used in Optical Parametric Amplifiers (OPA). Parametric laser light generation was reviewed in [8.77,78]. 

In the CARS process the sample is irradiated by two laser beams and the frequency difference between the beams is chosen to correspond to the vibrational (rotational) splitting of the irradiated molecules. The beams are denoted the pump beam (at frequency cjp) and the Stokes beam (at frequency c s). Two photons of frequency Wp are mixed with a photon of frequency c s, through the third-order susceptibility to generate a stimulated anti-Stokes photon of frequency (in the anti-Stokes position with regard to the pump beam) 

It can be seen that, apart from the doubled frequencies, sum and difference frequencies are obtained. The phase matching is chosen to strongly enhance one of the tern. In Fig. 8.38 curves for sum generation employing a dye laser and the fundamental fr-equency of the NdrYAG laser are given. 

For difference-frequency generation materials that are transpar ent in the IR region are needed. In Fig. 8.39 IR generation in LiNbOa (lithium niobate) is illustrated employing single-mode Ar and dye lasers, and output curves 

Frequency mixing can also be achieved in mixtures of metal vapours and inert gases. Since asymmetry is not present in a gas, terms depending on are excluded. Third-order processes ( ) 0) can be utilized. Direct frequency tripling and four-wave mixing processes are of this type. 

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We now embark on a more fonnal description of nonlinear optical phenomena. A natural starting point for this discussion is the set of Maxwell equations, which are just as valid for nonlinear optics as for linear optics. 

Microscopy methods based on nonlinear optical phenomena that provide chemical information are a recent development. Infrared snm-frequency microscopy has been demonstrated for LB films of arachidic acid, allowing for surface-specific imaging of the lateral distribution of a selected vibrational mode, the asymmetric methyl stretch [60]. The method is sensitive to the snrface distribntion of the functional gronp as well as to lateral variations in the gronp environmental and conformation. Second-harmonic generation (SHG) microscopy has also been demonstrated for both spread monolayers and LB films of dye molecules [61,62]. The method images the molecular density and orientation field with optical resolution, and local qnantitative information can be extracted. 

Nonlinear optical phenomena, as well as near-field optics, provide us with super resolving capability [20]. The probability of nonlinear optical phenomena is proportional to the number of photons which participate in the phenomenon. For example, the intensity distribution of two-photon excited fluorescence corresponds to the square of the excitation light. Thus, we proposed a combination of the field... 

Tichonov EA, Shpak MT (1979) Nonlinear optical phenomena in organic compounds. Naukova Dumka, Kijiv (in Rus)... 

Two straightforward third-order nonlinear optical phenomena which are used to characterize ft and y are EFISH and THG (2)... 

Butcher, P. N. "Nonlinear Optical Phenomena" Ohio State University Engineering Columbus, 1965-... 

Nonlinear ion traps, 15 662 Nonlinear materials, 14 680 Nonlinear optical materials, 17 442-460 advantage of, 17 448 classification of, 17 443—444 economic aspects of, 17 457-458 photorefractive materials, 17 457 second-order, 17 444r-453 third-order, 17 453—457 Nonlinear optical phenomena, 17 443 Nonlinear optics... 

One result of studying nonlinear optical phenomena is, for instance, the determination of this susceptibility tensor, which supplies information about the anharmonicity of the potential between atoms in a crystal lattice. A simple electrodynamic model which relates the anharmonic motion of the bond charge to the higher-order nonlinear susceptibilities has been proposed by Levine The application of his theory to calculations of the nonlinearities in a-quarz yields excellent agreement with experimental data. 

Therefore after scaling it could serve as thermometer. The complicated processes involved in de- and re-colouration are not fully understood, but the latter is undoubtedly associated with the complex decomposition triggered by thermal motion of the cyclo dextrin involved. Thus it reflects the dynamic character of the phenolophthalein complex with 11 (see Section 3.4 for a short discussion of dynamic character of supramolecular complexes). Optoelectronics making use of nonlinear optical phenomena is yet another field of prospective applications of molecular assemblies [32]. 

Several other applications of supramolecular systems have been proposed. Amongst those that are thought to be capable of bringing enormous benefits are devices making use of nonlinear optical phenomena [3,127]. Another exciting possibility of application of supramolecular systems includes the use of nematic... 

R. Tanas, Quantum noise in nonlinear optical phenomena, first chapter in Part 1 of this three-volume set. 

J. Perina, Quantum Statistic of Linear and Nonlinear Optical Phenomena, Kluwer, Dordrecht, 1991. 

Khoo. lam-Choon C. Liquid Crystals Properties attd Nonlinear Optical Phenomena. 

The theoretical problems associated with calculating nonlinear polarizabilities is closely linked to the field of charge transfer spectroscopy and reactivity as well as the field of multi-photon and excited state spectroscopy. It is likely that theoretical methods from these fields will contribute to a deeper understanding of nonlinear optical phenomena in organic, inorganic, and organometallic compounds. 

Two classes of material will be described here - the metal dithiolenes and rare earth metallocenes. In the metal dithiolenes a strong, low energy pi-pi transistion occurs in the near IR (9.10). This can be tuned from about 700 nm to 1400 nm by altering the metal ion, substituents or charge state of the dithiolene. The dithiolenes are particularly attractive because of their optical stability which has been exploited in their use as laser Q-switch materials. In the rare earth complexes the near IR band is provided by/-/transistions of the rare earth ion rather than the cyclopentadienyl ring structure various nonlinear optical phenomena have been observed in glasses incorporating similar ions. Previous studies have shown that dicyclopentadienyl complexes such as ferrocene have off-resonant nonlinearities similar to nitrobenzene or carbon disulphide (11-13)... 

IC Khoo. Liquid crystals Physical Properties and Nonlinear Optical Phenomena. New York Wiley, 1995. 

Vogel, E.M., Weber, M.J. and Krol, D.M. (1991) Nonlinear optical phenomena in glass, Phys. Chem. Glasses, 32, 231-54. 

Optical nonlinearities can be explained by considering the interaction of strong electric fields with matter. If the fields have optical frequencies, the phenomena resulting from the nonlinear interactions are called nonlinear optical phenomena. Most texts on nonlinear optics (e.g., Refs. 22-25) begin the discussion of this area from considerations of macroscopic relations between the vector quantities P (the polarization vector), D (the displacement vector), and E (the electric field vector). Chemists, however, consider the molecular origin of physical phenomena, so the description of NLO phenomena that follows starts from consideration of the behavior of a single molecule in a strong electric field. 

With intense laser pulses, new nonlinear optical phenomena are possible. The prime example is two-photon excitation (TPE). The peak power in a laser pulse from a Ti sapphrre laser (pulse width 100fs) can readily reach 10 W or higher, with a focused intensity of lO W/cm. Under these conditions, excitation can occur with two photons that have half of the energy (twice the wavelength) of the corresponding one-photon transition (see Fig. 2a). The rate of TPE is given by ... 

In a similar manner, one can also consider third-order nonlinear vibrational spectroscopy. CARS is one of well-known third-order nonlinear optical phenomena... 

Hi h-performance optical materials 1-d Nonlinear optical phenomena Photoinduced electron transfer Photovoltaic devices Tunable NLO properties... 

Studies of nonlinear optical phenomena in conjugated polymers date back to the earliest studies of the polydiacetylenes [219], The large oscillator strength associated with the p-p transition gives rise to a relatively large linear electronic polarizibility. The early work speculated that because of the implied delocalization of charge in the excited state, conjugated polymers would offer opportunities as NLO materials. 

Wendorff, J. H., and Eich, M. Nonlinear optical phenomena in liquid crystalline side chain polymers. Mol. Cryst. Liq. Cryst. 169, 133 (1989). 

PHOTOINDUCEDTHIRD-ORDER NONLINEAR OPTICAL PHENOMENA IN AZO-DYE POLYMERS... 

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