Volume 94, Issue 6, 15 September 2003
Index of content:
- LASERS, OPTICS, AND OPTOELECTRONICS (PACS 42)
Jones matrix method for predicting and optimizing the optical modulation properties of a liquid-crystal display94(2003); http://dx.doi.org/10.1063/1.1601688View Description Hide Description
We present a simple technique for the calibration, prediction, and optimization of the optical modulationproperties of a liquid-crystal display(LCD). The method is useful when there is no information about the internal fabrication parameters of the device (the orientation of liquid-crystal molecules, the twist angle, or the birefringence of the material). A complete determination of the LCD Jones matrix is accomplished by means of seven irradiance measurements for a single wavelength. This technique only requires two linear polarizers and one quarter-wave plate. Once the Jones matrix has been calibrated, the amplitude, phase, and polarization modulation response can be predicted. Therefore, it can be optimized through the control of the polarization configuration. The validity of the proposed method is experimentally probed. Finally, we present a particular application to produce phase-only modulation.
Effects of classical and quantum charge fluctuations on sequential electron tunneling in multiple quantum wells94(2003); http://dx.doi.org/10.1063/1.1594815View Description Hide Description
A previous theory [M. Ershov et al., Appl. Phys. Lett. 67, 3147 (1995)] for studying the distribution of nonuniform fields in multiple-quantum-well photodetectors under an ac voltage is generalized to include nonadiabatic space-charge-field effects. From numerical results calculated by the generalized theory, it is found that field-domain effects are only important at high temperatures or high voltages, where both injection and sequential-tunneling currents are expected to be large. On the other hand, field-domain effects become negligible at low temperatures and low voltages, but nonadiabaticeffects included in this extended theory are enhanced for small sequential-tunneling currents. The time duration for nonadiabaticeffects is determined by the quantum capacitance. By using the generalized theory, a differential capacitance is calculated for a non-steady state, and a negative conduction current is predicted under a positive voltage in this case due to charge accumulation around the collecting contact.
94(2003); http://dx.doi.org/10.1063/1.1603344View Description Hide Description
The left-handed property of a metamaterial is demonstrated by measuring the power at the output of a T-junction waveguide loaded with a metamaterial having one edge cut at 45° with respect to the waveguide axis. Both experimental scattering data and numerical results are presented. The metamaterial sample is realized by using a periodic arrangement of wires and split-ring resonators, and the operating frequency is chosen to correspond to a refraction index of about The results show that when the T junction is empty, most of the power is received at the output port directly facing the input port, whereas when it is loaded with the sample of metamaterial, most of the power is received at the output port perpendicular to the input axis. This indicates that the energy is bent by the oblique edge of the sample by an angle of with respect to the normal, which suggests a negative index of refraction.
94(2003); http://dx.doi.org/10.1063/1.1602571View Description Hide Description
We optimize the water-window x-ray flux and debris deposition for a liquid-jet laser plasma source by varying both the target diameter and the jet material. For two target liquids, methanol and ethanol, measurements of the C VIx-ray flux and the debris deposition rates are presented as function of the jet diameter. It is shown that the effective carbon debris deposition is more than 1 order of magnitude smaller for methanol, while the x-ray flux is reduced only ∼40%. The reduction in carbon debris deposition may be explained by reactive ion etching by oxygen from the plasma. Thus, the methanol water-window source may be operated at a 5–10× higher flux without increasing the debris deposition. The optimization potentially allows a reduction of the exposure time of compact soft x-ray microscopy or other water-window applications based on such sources without increasing damage to sensitive x-ray optics.