Electro-optic experiment

The amplitude of the saturated ionic dipole moment is found to be independent of the molecular weight in Stellwagen s electro-optical experiments for DNA restriction fragments [81], although the theory of Sokerov and Weill [82] predicts quadratic dependence of this moment on the polyion length. The diversity of results implies that not all aspects of the molecular weight dependence of the LF effect are well understood and further inves-... 

This chapter is concerned with experimental measurements of flexo-electric coefficients. After a brief introduction to flexoelectricity in nematic liquid crystaJs, some applications exploiting the flexoelectric effect and the influence of this effect on electrohydrodynamic instabilities are pointed out. Flexoelectricity axises in samples with a splay-bend distortion in the director field and as such its measurement is not as direct as for dielectric constants. The theoretical background needed to analyse electro-optic experiments and extract the flexocoefficients is outlined in Section 2.2. Various experimental techniques that have been developed are described in Section 2.3. These involve cells in which the alignment of the nematic director is homeotropic, or planar or hybrid. In the first case, the interdigitated electrode technique is particularly noteworthy, as it has been used to establish several features of flexoelectricity (1) the effect can arise purely from the quadrupolar nature of the medium, and (2) the dipolar contribution relaxes at a relatively low frequency. 

In this thesis Johanna Bruckner reports the discovery of the lyotropic counterpart of the thermotropic SmC phase. By means of polarizing optical microscopy. X-ray diflfraction and electro-optic experiments she firmly establishes aspects of its stmcture and elucidates its fascinating properties, among them a pronounced polar electro-optic effect, analogous to the ferroelectric switching of its thermotropic counterpart. The helical ground state of this new lyotropic phase raises the fundamental question of how chiral interactions are communicated across layers of disordered and achiral solvent molecules which are located between adjacent... 

The Frederiks transition in linear-chain and comb-like polymers may be treated in an analogous way as low-molecular-weight compounds, with some precautions [13], because, in general, the electric and viscoelastic properties of liquid crystal polymers are field dependent and the response of the materials to an external field is essentially nonlinear. Unfortunately, in the major part of electro-optical experiments this nonlinearity is not taken into account and results are interpreted in terms of conventional nema-todynamics and constant material parameters. In addition, in only a few papers (e.g. 

A copolymer (DCV-MMA) of methyl methacrylate and 4,4(dicyano-vinyl)-4 -(dialkylamino)azobenzene-substituted methacrylate (Fig. 4.9) formed by a novel azo coupling reaction [67] has been used [68] for corona poling and electro-optic experiments. The DCV-MMA has a Tg of 127 °C and when poled exhibits a 33 value of 5.1 x 10 esu, relaxing to 4.6. This... 

In this brief survey the author will outline a number of electrooptical methods in current use and give illustrative results wiiich demonstrate their practical utility. Theory for the various effects will be given predominantly for cylindrically symmetric molecules which are rigid, uncharged and non-interacting as this is the best developed to date and allows a useful comparison between the methods. Reference will be made to work done on flexible systems. The object of this survey is primarily to introduce those scientists who are on the look-out for novel methods to characterise macromolecules in dilute solution to electro-optic experiments and to demonstrate the potential and versatility of the methods. The selected illustrative data on various polymer solutions are not intended to be comprehensive. They have simply been drawn from studies conducted in the author s research group. 

Fig. 6. Cells used in various electro-optic experiments. In (a) the field is transverse to the light path as for birefringence and dichroism experiments, (b) is the multireflecting cell for electric dichroism. In (c) the multi de cells are also arranged in longitudinal array for optical rotation experiments, (d) are light scattering cells with hmizontal and vertical electrodes as shown...

Experiments on transport, injection, electroluminescence, and fluorescence probe the spatial correlation within the film, therefore we expect that their response will be sensitive to the self-affinity of the film. This approach, which we proved useful in the analysis of AFM data of conjugated molecular thin films grown in high vacuum, has never been applied to optical and electrical techniques on these systems and might be an interesting route to explore. We have started to assess the influence of different spatial correlations in thin films on the optical and the electro-optical properties, as it will be described in the next section. 

Until recently a general drawback of this passive Q-switching scheme was the difficulty of obtaining an exact synchronization of the giant pulse with other events in more complex experiments. This difficulty does not exist with active Q-switching in which an electro-optic device, e.g. a Kerr-cell or Pockels-cell, is used instead of a dye cell, and one is able to determine exactly the time at which... 

The formation of boundary layers at the surface interface between semiconductor and gas influences also the luminescence and the electro-optical qualities of semiconductors. These effects offer interesting possibilities for studying experimentally the mechanism of chemisorption, the stationary state of chemisorption, and electron defects in the catalyst during catalysis. Experiments along this line have been carried out by some investigators (40,41) who have studied in a qualitative way the factors influencing the oxidation of phenols catalyzed by zinc oxide under the influence of light. Further work on this subject is desirable. 

In anisotropic materials, the electronic bonds may have different polarizabilities for different directions (you may think of different, orientation-dependent spring constants for the electronic harmonic oscillator). Remembering that only the E-vector of the light interacts with the electrons, we may use polarized light to test the polarizability of the material in different directions, lno is one of the most important electro-optic materials and we use it as an example. The common notations are shown in Figure 4.7. If the E-vector is in plane with the surface of the crystal, the wave is called a te wave. In this example, the te wave would experience the ordinary index na of LiNbOs (nG 2.20). If we rotate the polarization by 90°, the E-ve ctor will be vertical to the surface and the wave is called tm. In lno, it will experience the extraordinary index ne 2.29. Therefore these two differently polarized waves will propagate with different phase velocities v c/n. In the example of Figure 4.7, the te mode is faster than the tm mode. 

The dielectric tensor describes the linear response of a material to an electric field. In many experiments, and particularly in optical rheometry, anisotropy in is the object of measurement. This anisotropy is manifested as birefringence and dichroism, two quantities that will be discussed in detail in Chapter 2. The nonlinear terms are responsible for such effects as second harmonic generation, electro-optic activity, and frequency tripling. These phenomena occur when certain criteria are met in the material properties, and at high values of field strength. 

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... 

In 1875 John Kerr carried out experiments on glass and detected electric-field-induced optical anisotropy. A quadratic dependence of n on E0 is now known as the Kerr effect. In 1883 both Wilhelm Rontgen and August Kundt independently reported a linear electro-optic effect in quartz which was analysed by Pockels in 1893. The linear electro-optical effect is termed the Pockels effect. 

For certain macroscopic nonlinear parameters the tensor notation can be simplified due to the intrinsic symmetry of the experiment, e.g., second-harmonic generation and the linear electro-optic effect. Let us first consider SHG. The second-order contribution to the polarization is given by Eq. (9). 

We wish to extend our personal thanks to the many persons associated with the warm core ring experiments and with the AOL project. In particular, we are indebted to Jack L. Bufton and the Instrument Electro-Optics Branch for the loan of the frequency-doubled YAG laser. We also thank Wayne E. Esaias and the Oceanic Processes Branch of NASA Headquarters for their assistance and encouragement in various aspects connected with these experiments. 

Frank A. Horrigan retired from the technical development staff for sensors and electronic systems at Raytheon Systems Company. Dr. Horrigan has a background in technologies relevant to military systems, in particular, radar and sensor technologies. A theoretical physicist, he has more than 37 years experience in advanced electronics, electro-optics, and advanced information systems. In addition, he has experience in planning and managing industry research and... 

In brief, we propose the TOT electro-optical setup in which electrical measurements have a high quality factor combined with the coherence of an all optical experiment. The TOT can be easily incorporated in electrical circuits as a nonlinear element ensuring a scalability of the architecture. The quantum dot isolation in the TOT will protect entanglement of quantum states thus permitting field programmable gates arrays. 

---