Optical nonlinearity measurement

Barzoukas and Blanchard-Desce proposed an approach of molecular engineering using multivalence-bond state models [55]. Push-pull polyenes were shown also to present an enhancement of the TPA response and a loss of transparency of molecules, as a function of the increase of the polyenic chain length [56,57]. Trends observed in these polyenic systems are supported by the large third-order optical nonlinearities measured in asymmetric carotenoids, in which the role of the large value of dipole moment difference A/z was shown [58]. 

The second order optical nonlinearity shown in these figures has been measured by second harmonic generation as previously described. Relevant optical data and measured values of optical nonlinearity (measured for the polymer systems reported in this communication) are summarized in Table 1. 

For measurements carried out closer to resonances, thermal contributions to the optical nonlinearity, given by the following formula, can compete with electronic contributions (54,55) ... 

These structure-function relationships provide extremely useful guidance for the future rational design of molecules and polymers with even higher optical nonlinearities. For non-centrosymmetric molecules such as 95, very high first hyperpolarizabilities /3 that determine the second-order nonfinear optical properties were also measured [140]. 

Sheik-Bahae, M., Said, A. A., Wei, T. H., Hagan, D. J. and Van Stryland, E. W. (1990) Sensitive measurement of optical nonlinearities using a single beam. IEEE J Quantum Electron., 26, 760-769. 

Sheik-Bahae M, Said AA, Wei TH, Hagan DJ, Van Stryland EW (2007) Special 30th anniversary feature sensitive measurement of optical nonlinearities using a single beam. IEEE LEOS Newslett 21 17-35... 

Although a great deal of data analysis is needed to obtain a value of the optical nonlinearity from this measurement, we can estimate the order of magnitude of the value. The estimate comes from a comparison of this data with that taken on a similar experiment using Si as the nonlinear material. (15) The two experiments used approximately the same laser power and beam geometry, and the linear reflectivity curves were similar in shape and size (the minimum value of reflectivity). Neglecting differences... 

Using the alternating deposition of the amphiphiles with a carboxyl substituent and arachidic add, noncentrosymmetric LB films (hetero Y-type) were prepared, and molecular orientation and second-order optical nonlinearity in the LB films were evaluated with the linear dichroism [4] and the second-harmonic generation (SHG) measurements, respectively. The SHG measurement procedure is mentioned in the section 1.3. 

Third-order optical nonlinearity of the oriented MOPPV LB film was evaluated by the THG measurement [30]. The detailed procedure is described in the section 2.1. 

At a fundamental wavelength of 1064 nm, large and anisotropic optical nonlinearity was also observed. The values of X (3) and are 4.5 x 1010 esu and 1.0 x 10 10 esu, respectively. The large values are due to the two photon resonance, because the harmonic wavelength of 355 nm is near off-resonance region. From the two-photon fluorescence measurement, we confirmed that a two-photon absorption band, which is origin of the enhancement effect, exist around 532 nm, half of the fundamental wavelength. 

Shcheslavskiy, V., Petrov, G. I., and Yakovlev, V. V. 2003. Nonlinear optical susceptibility measurements in solutions using third-harmonic generation at interfaces. Appl. Phys. Lett. 82 3982-84. 

Sulfur heterocycles, including those with more than two sulfur atoms, are used for optical materials <2000JPP2002040201>. The molecular third-order optical nonlinearity 7R (Second hyperpolarizability or nonlinear refractive index) was measured for pentathiepinethiafulvalene <1999PCA6930>. 

The work described in this paper represents the contributions of several people. Laura Davis is responsible for the linear optical property measurements and the development of the microreffactometer. Most of the nonlinear optical measurements on small single crystals have been made by Mark Webb, who is also responsible for several improvements in the apparatus and technique. Francis Wang synthesized the chiral organic salts and did the powder SHG measurements. David Eimerl was the source of much encouragement, advice, and support during the course of this work. 

Fig-2. Correlation of ionic conductivity with poling efficiency (second-order nonlinear optical activity). The upper graph shows conductivity measured as a function of temperature while the lower graph shows second-order nonlinear optical activity (measured by second harmonic generation, SHG) as a function of temperature. Note that second-order NLO activity starts to decrease with the onset of conductivity. Conductivity in this case was shown to arise from ionic impurities... 

Assessing thermal and photochemical stability is important. Thermal stability can be readily measured by measuring properties such as second harmonic generation as a function of heating at a constant rate (e.g., 4-10 °C/min) [121]. The temperature at which second-order optical nonlinearity is first observed to decrease is taken as defining the thermal stability of the material [2,3,5,63,63]. It is important to understand that the loss of second-order nonlinear optical activity measured in such experiments is not due to chemical decomposition of the electro-optic material but rather is due to relaxation of poling-induced acentric... 

Since all these excitations possess clear spectroscopic fingerprints, a very powerful tool for studying their photophysics is the so-called pump-and-probe technique, which can be related to the optical nonlinearities of the material. As far as optical properties are concerned, the change in refractive index upon excitation (An or Ak), either optical or otherwise, is the nonlinear part of the optical response. Traditionally two approaches have been developed to measure nonlinearities, based on different techniques ... 

Similar methods have been used to prepare CdS NCs in optical quality borosilicate glasses." Nonlinear optical characterization of one composite sample with particle sizes ranging from 2.5-5.5nm yielded a range for of 10 -10 esu. Optical gain measurements of a similar material afforded a value of 33 cm at room temperature. At 11 K, maximum gain values reached 200 cm , and like the optical nonlinearities, these values were also dependent on NC concentration. ... 

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