Particle-Based Optical Devices
Organic and polymer nanocrystals prepared by the reprecipitation method, including the SCR, RMI and IR techniques (see Chap. 2), have been obtained as a dispersion liquid [1 , 2 , 3 ]. Nanocrystals are remarkably stable, when dispersed in a medium, becaus
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Particle-Based Optical Devices
H. Oikawa and H. Nakanishi
29.1
Introduction
Organic and polymer nanocrystals prepared by the reprecipitation method, including the SCR, RMI and IR techniques (see Chap. 2), have been obtained as a dispersion liquid [1-3]. Nanocrystals are remarkably stable, when dispersed in a medium, because of the highly negative (-potential [4]. As described in Chap. 14, poly(DCHD) nanocrystal thin films with high optical quality and very low scattering loss can be conveniently fabricated by utilizing this character of nanocrystals dispersed in an aqueous liquid. From an alternate view point, the organic nanocrystal dispersion system itself is of much interest, and usually behaves as a random and isotropic phase. However, once organic nanocrystals could respond sensitively to applied external potentials like electric and/or magnetic fields, polarized light, and flow field, the dispersion system is converted from a random phase to an oriented and anisotropic phase, which may cause changes of the optical properties such as transmittance and refractive index in the whole dispersion system. In the present chapter, our attention is focused on nanocrystal-based optical devices as two detailed examples. One is an optical switching device based on a Fabry-Perot optical oscillator, and the other is the electric-field-induced orientation of organic nanocrystals. To achieve orientation under an applied electric field, two factors are required: to use organic polar nanocrystals having a dipole moment, and to use a dispersion medium with low dielectric constant. The dipole moment is of course necessary to respond to the applied electric field, while the latter is required to apply effectively the electric field to organic polar nanocrystals. According to these two factors, the dispersion system of DAST nanocrystals dispersed in decalin has been chosen for the experiments [5,6]. DAST is well-known to be one of the most promising materials as a functional ionic chromophore for a second-order NLO (SHG-active) material [7-9].
29.2
Optical Switching by the Fabry-Perot Optical Oscillator
We attempted to confirm the fringe pattern in the transmission spectra from a Fabry-Perot optical oscillator [10]. In general, Fabry-Perot cavities with nonH. Masuhara et al. (eds.), Single Organic Nanoparticles © Springer-Verlag Berlin Heidelberg 2003
29 Particle-Based Optical Devices
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Fig. 29.1. Fringe pattern typically obtained from a Fabry-Perot optical resonator combined with nonlinear optical materials (n2 > 0): (a) without pump beam, (b) with pump beam linear spacer layers have been recognized as useful structures for all-optical switching, as shown in the typical fringe patterns in Fig. 29.1. In addition, poly(DCHD) nanocrystals exhibit significant near-resonant (640 nm) optical nonlinearity and induced transparency [11]. These characteristics of absorption bleac
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