Volume 96, Issue 12, 15 December 2004
Index of content:
- LASERS, OPTICS, AND OPTOELECTRONICS (PACS 42)
96(2004); http://dx.doi.org/10.1063/1.1811374View Description Hide Description
We report the fabrication of widely tuneable optically pumped two-dimensional distributed feedback polymer lasers that utilize a red-emission fluorene copolymer as the active gain medium. The lasers exhibit efficient, low threshold operation and emit highly directional output beams as a result of the enhanced two-dimensional photonic confinement provided by the employed resonator. Their emission and operating characteristics are described in detail. We demonstrate that the very wide spectral range over which these lasers can be systematically tuned is in very good agreement with theoretical predictions based on a simple waveguide model. In addition, we show that the lasers have long operating lifetimes pulses and we discuss the impact that degradation has on the laser output characteristics.
96(2004); http://dx.doi.org/10.1063/1.1810204View Description Hide Description
We present two methods based on the analysis of Fabry-Pérot interference for a detailed characterization of a 90° corner in a two-dimensional photonic crystal waveguide fabricated in a thin Si membrane. These methods are a means of identifying the critical waveguide elements in the process of improving photonic crystal devices. The effects of the elements forming the photonic crystal waveguide are identified and quantified by means of a stage-by-stage analysis. By Fourier transforming the transmission spectra we observe the amount of light that is back reflected inside the waveguide and based on the fringe contrast of the Fabry-Pérot modulation we calculate the loss contribution of each waveguide element, such as the tapers and the 90° corner.
96(2004); http://dx.doi.org/10.1063/1.1806534View Description Hide Description
A heterodyneinterferometry technique for parallel photodisplacement imaging is presented. In the parallel photodisplacement technique, a linear region of photothermal displacement is excited using a line-focusing intensity-modulated laser beam and is detected with a parallel heterodyneinterferometer in which a charge-coupled device linear image sensor is used as a detector. The integration and sampling effects of the sensor provide spatiotemporally multiplexing of the interference light. To extract the spatially resolved photodisplacement component from the multiplexed sensor signal for heterodyneinterferometry, a scheme of phase-shifting light integration under an undersampling condition is developed. The frequency relation for the heterodyne beat signal, modulation signal, and sensor gate signal is optimized so as to eliminate undesirable components, allowing only the displacement component to be extracted. Preliminary experimental results using a point-focused laser beam demonstrate that the technique is effective, making it possible to accurately extract photodisplacement components from the multiplexed interferogram. Subsurface structures and defects in silicon wafers are clearly imaged with a detection time of . In combination with a line-focusing laser beam, this technique is very promising for high-throughput subsurface imaging with detection speeds more than 10 000 times faster than conventional photoacoustic microscopy.
96(2004); http://dx.doi.org/10.1063/1.1814807View Description Hide Description
Wormhole liquid crystal display modes are proposed. Micron-sized and randomly arranged holes on upper and lower electrodes are formed in order to deform a liquid crystal alignment. By optimizing cell thickness, the calculation of director profiles and transmittance based on Frank’s continuum theory and Jones matrix are carried out and the maximum transmittance is compared with experimental results. Good transmittance versus voltage characteristics was obtained regardless of the sign of the dielectricanisotropy. From optical microscopy, radial and spherical domains were found at the electrode holes. The position of these domains was randomly arranged and its shape was that of a half-cut droplet. Electro-optical response and viewing angle characteristics have also been evaluated.
96(2004); http://dx.doi.org/10.1063/1.1815383View Description Hide Description
The angular and wavelength selectivity of noise gratings in doped strontium barium niobate crystals for samples with two different thicknesses are investigated. We found that an offset in the optimum reconstruction angle with respect to the recording geometry occurs as a function of the thickness. This is a consequence of the unidirectional amplification. Thus the scattering intensity for the thinner sample is considerably lowered at the very recording conditions. We analyze the experimental results in terms of the kinematic theory of diffraction.