Third-order nonlinear optics characterizations

Characterizations bv Third-Order Nonlinear Optical Experimentation... 

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

This paper is a tutorial overview of the techniques used to characterize the nonlinear optical properties of bulk materials and molecules. Methods that are commonly used for characterization of second- and third-order nonlinear optical properties are covered. Several techniques are described briefly and then followed by a more detailed discussion of the determination of molecular hyperpolarizabilities using third harmonic generation. 

On the route to all-optical signal processing the development of materials with large third-order nonlinear optical effects is of decisive importance. For the material characterization and the assessment of its usefulness for applications the absolute value of the third-order nonlinear optical susceptibility y has to be known. Since most measurements are performed relative to a reference material, the establishment of a well accepted value for a standard material is important. 

The most widely employed material characterization techniques in third-order nonlinear optics are third-harmonic generation (THG) [21], degenerate four wave-mixing (DFWM) [22], Z-scan [6], and optical limiting by direct two-photon absorption (TPA) and fluorescence spectroscopy induced by TPA [23]. All of them will be discussed in the following. Further measurement techniques such as electric-field induced second-harmonic generation (EFISH) [24], optical Kerr... 

Jiang, C.-W., Chao, H., Li, R.-H., Li, H., Ji, L.-N. Syntheses, characterization and third-order nonlinear optical properties of ruthenium(II) complexes containing 2-phenylimidazo-[4,5-/][l,10]phenanthroline and extended diimine ligands. Polyhedron 20, 2187-2193 (2001)... 

The functionalized polymers appear to be attractive materials for third order nonlinear optical applications. They are characterized by small propagation losses (wave-guiding devices. Although their nonlinear optical response is lower than that... 

In order to fully use the potential of various structures prepared by this technique, an important step is a careful characterization of L-B films. In our laboratory, a number of spectroscopic and surface-sensitive techniques are used. Both second and third-order nonlinear optical processes have been observed using L-B films. The organization of this paper is as follows. First, some of the techniques used for the characterization of L-B films are discussed. Then some interesting examples of control of order and conformation in the L-B films are presented. This is followed by a subsection, which presents results of the study of both second and third-order nonlinear optical processes in L-B films. Finally, possible applications of L-B films in nonlinear optical devices are discussed. 

Micron- and submicron-scale lateral structures of optically nonlinear organic films comprised of substituted trons-stilbene derivatives (Ri = OCH3, R2 = CN) was characterized [45]. Second harmonic generation (SHG), optical microscopy, and atomic force microscopy (AFM) were used in this investigation. The third-order nonlinear optical properties and two-photon absorption ofdifferent types of stilbene derivatives (D-tt-D, A-7t-A, D-7t-A) were investigated [46]. Using the INDO/CI method, the UV-vis spectra were explored and the position and strength of the two-photon absorption were predicted by sum-over-states expression. Relationships of the structures, spectra, and nonlinear optical properties have been examined. Two-photon absorption spectra (650-1000 nm) of a series of asymmetrically substituted stilbenoid chromophores... 

The terminally substituted diphosphines have also been used to prepare Au complexes (16-18, Chart 5.4) [37]. The metal does not shift the absorption maxima much relative to the free ligands however, dual emission is observed in the case of 17. This is attributed to emission from both monomer and an Au-Au bridged dimer, which is observed in the solid state. Several of the Pt and Pd complexes (19-24, Chart 5.4) have also been characterized crystallographically and some of these structures show k-k stacking interactions between thiophene rings in the solid state [38]. A third-order nonlinear optical response was obtained for the Pd and Pt complexes (21 and 24) using Z-scan measurements [39]. These complexes have nonlinear refractive index values of (—1.5 to —1.8) Hicks and co-workers have prepared a... 

PHTs, which are characterized by a highly conjugated structure, have attracted interest for their third-order nonlinear optical response PT in particular has been actively investigated [330]. 

Characterization of Third-Order Nonlinear Optical Properties in... 

Keywords Characterization techniques, Second-order nonlinear optical response, Third-order... 

Because of their large optical nonlinearities and good mechanical, chemical, thermal, and optical stability, organic nonlinear materials are among the leading practical materials for device applications [2]. A number of experimental techniques have been proposed to obtain information about the dispersion, the sign, and the contributions of both the real and imaginary parts of the nonlinear optical response. In this chapter, we will explore the methods most widely used to characterize the third-order nonlinear coefficient and introduce some of the more recent results. 

Several of the third-order nonlinear effects described in section 4.1.3 can be used to characterize bulk materials. Degenerate four-wave mixing (DFWM) is used for measuring third-order properties of films and solutions [43-45], and though this experiment is complex to set up and interpret, it can give valuable information on the magnitude, sign and speed of the nlo process, as well as an indication of the nature of the excitation process. Results from DFWM can be found in section 4.3. Optical Kerr effect (OKE) [46] and electrical Kerr effect (EKE) [47] measurements have also been used to characterize third-order properties of nlo polymers. It is important to note that THG, DFWM, OKE and EKE all measure different parts of the third-order susceptibility, and... 

Electrodeposited sol-gel-based composite films also showed optical applications. Gu and coworkers [85,86] co-electrodeposited Te0 > -Si02 hybrid films from the TEOS-Te(i-PrO)4 niixed precursor for nonlinear optics. Te(IV) was partially reduced during electrodeposition, as characterized by EDX of the obtained films. The as-prepared films had third-order nonlinear susceptibility ix ) of 5.9 X10 to 4.29 X 10 esu, and the films had of 1.551 X 10 esu after posttreatment annealing. Mandler and coworkers co-electrodeposited TMOS with multiwalled carbon nanotubes (MWCNTs) on ITO and silver. The optimized films electrodeposited on ITO showed transparency of about 50% with nonlinear optical properties, and the optimized films electrodeposited on silver had specular reflectance lower than 0.5% in the wavelength range of 400-15 000 nm, which can be used as antireflection coatings. 

Out of the large range of possible nonlinear optical effects, chemists are likely to encounter only a limited number of measurement techniques. These include both second- and third-order NLO characterization methods. A brief listing of the different types of measurements, the nonlinear susceptibility involved and the related molecular nonlinear polarizabilities is given here. 

We have presented a review of the salient features of nonlinear integrated optics. It appears that nonlinear organic materials can play an important role in second- and third-order guided-wave devices. This field requires a great deal of material characterization and processing, however, before significant advances are realized. 

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