Polarization conversion

Theoretically, for a given chemical nature, the immersion energy of a nonporous solid should be proportional to the surface area and the corresponding coefficient should be available from a reference solid of known surface area. Nevertheless, the detailed surface composition and structure of solids with similar bulk composition and even crystaUinity can be very different because of their chemical, mechanical or thermal history. Therefore, it would be unwise to use the relative measurement of surface area when both the surface and the immersion liquid are polar. Conversely, nonpolar hquids can be used for such a determination because the corresponding immersion energies are not sensitive to minute variations of the surface chemistry. This point will be addressed again later on in the case of microporous samples. 

CHROMATIC POLARIZATION CONVERSION OF TERAHERTZ RADIATION BY A DENSITY-MICROSTRUCTURED TWO-DIMENSIONAL ELECTRON SISTEM... 

Results of a theoretical investigation of the chromatic polarization conversion of the electromagnetic wave in a density-modulated two-dimensional (2D) electron system are presented. Numerical calculations are performed with the characteristic parameters of an actual 2D electron system in the electron inversion layer on p-Si at the terahertz frequencies. 

Due to the symmetry constraints in a 2D electron system with a periodically modulated electron density, one can anticipate that strong chromatic conversion of the EW polarization will occur due to resonant coupling between the EW and plasma oscillations even without dc magnetic field applied. The theory of EW polarization conversion in the 2D electron system with a rectangular electron density profile was developed within the first principles electromagnetic approach... 

In this paper we employ this theory to analyze the chromatic polarization conversion of terahertz (THz) radiation in such systems. 

Here we present further results on the angle dependence of the polarization conversion spectra. It follows from Fig.l that the resonant frequencies... 

Figure 1. Polarization conversion resonance curves (a) for different angles of incidence when t=45° and (b) for different azimuthal angles

In Fig. 2 we show the dependence of azimuthal angle (pmdielectric constants 2 / i It is seen that

contrast ratio. The value of max 5° at 0=0 is also independent of a particular profile of electron density distribution in 2D system as well as the modulation factor Ans= NA N )l(NA+N ). At 0 O the value of is smaller than 45°. A smaller contrast ratio corresponds fo smaller (p max- The value of

total reflection angle 0-0r because, in this case, the in-plane component of electric field in the plane of 2D electron system vanishes. 

Note that the solution of the problem of the incidence of an s-polarized EW onto a periodic density-modulated 2D electron system gives the same values for the polarization conversion coefficients = R ) in the TIR regime. This attests to a reciprocal character of the polarization conversion process for 0> Or,. 

Recent n-channel semiconductors have been conveniently developed by modifying the rr-frameworks of high-performance p-channel semiconductors with strong electron-withdrawing fluoro groups at the terminal positions. Takimiya et al. attempted the conversion of p-channel 2,6-diphenylbenzo [l,2- 4,5- ]diselenophene (53) into an n-channel semiconductor by means of this strategy. This polarity conversion was accomplished for 2,6-bis(4-trifluoromethylphenyl)[l,2-i> 4,5-ir ]diselenophene (56) [126]. 

Fig. 2.4 (a) Specifications of the three types of nanostructures used in numerical evaluation of the conversion eflSdency based on the FDTD method, and corresponding surface charge density distributions induced in each nanostmctuie. (1) Shape A only, (2) Shape B only, and (3) a stacked stiucture of Shapes A and B. (b) Calculated performance figure of the quadrupole-dipole transform, namely, polarization conversion elfidency, with the three types of nanostmctures. (c) Selective comparison at a wavelength of 690 nm... 

One of the reasons to use the Poincare sphere is that the effect of retardation films and the evolution of the polarization state can be easily visualized. We consider polarization conversion in the following few special cases. 

S.1 Polarization conversion using quarter-wave plates... 

Refractive index (and thickness) of thin films can be determined by ellipsome-try. This is a noninvasive technique that measures the polarization conversion... 

At that time, it is not the design of this reverse circular polarizing plate that the polarization emitted firom broad band XjA board returns polarization conversely and... 

As seen in Fig. 9.2, the observed polarization conversion properties, including the difference in polarization in the incident direction, were described on the basis of our simple binary model involving homogeneous and TN alignments. When the probe beam was incident on film A, the ellipticity of the diffracted beams was almost zero (the diffracted beams were LP). However, the diffracted beams were ellipticaUy polarized when the probe beam was incident on film B. The measured diffraction efficiencies of the 0th and lst order beams were approximately 51 % and 20 %, respectively, for any polarization state of the probe beam. This was also in reasonable agreement with the calculated diffraction efficiencies, which are 50 and 20 % for the 0th and lst order diffracted beams. 

In summary, using a two-step exposure method with a line-and-space photomask we fabricated an LC grating inner coated with PLCP photoalignment films. The diffraction efficiencies and the unique polarization conversion properties of the LC grating were well explained based on the simple binary model involving planar and TN alignments, the Jones matrix method, and diffraction theory. 

Ono H, Emoto A, Takahashi F, Kawatsuki N, Hasegawa T (2003a) Highly stable polarization gratings in photocrosslinkable polymer liquid crystals. J Appl Phys 94 1298-1303 Ono H, Emoto A, Kawatsuki N, Hasegawa T (2003b) Multiplex dif action fiom functionalized polymer liquid crystals and polarization conversion. Opt Express 11 2379-2384 Ono H, Emoto A, Kawatsuki N, Uchida E, Kuwabara M (2004) New fabrication method for anisotropic gratings formed in photocrosslinkable polymer liquid crystals. Appl Phys A 79 1725-1727... 

Khoo,I. C.,and J. Ding. 2002. All-optical cw laser polarization conversion at 1.55 micron by two beam coupling in nematic liquid crystal film. Appl. Phys. Lett. 81 2496-2498. 

Khoo, I. C., and A. Diaz. 2003. Nonlinear dynamics in laser polarization conversion by stimulated scattering in nematic liquid crystal films. Phys. Rev. E. 68 042701-1-4. 

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