Volume 92, Issue 8, 15 October 2002
Index of content:
- LASERS, OPTICS, AND OPTOELECTRONICS (PACS 42)
High-efficiency optical phase conjugation by degenerate four-wave mixing in volume media of disperse red 1-doped poly(methyl methacrylate)92(2002); http://dx.doi.org/10.1063/1.1509085View Description Hide Description
High-efficiency optical phase conjugation (PC) by degenerate four-wave mixing in stress-processed volume media of disperse red 1 (DR1)-doped poly(methyl methacrylate) in the transparent region (647 nm) is reported. With vertically polarized counterpropagating pump waves, PC reflectivities of 43% and 37% were achieved, respectively, for a horizontally and vertically polarized probe wave, which is 50 times higher than the value reported on resonance. Reflectivities over 30% were achieved over a wide range of intensity for both polarization configurations. Photoinduced reorientation of the DR1 chromophore through trans-cis-trans isomerization is the dominant mechanism for the PC wave generation. Other mechanisms involved in the configuration of all vertical polarization waves are also examined. The roles of the polymer matrix and azo-dye photoisomerization in this high-efficiency PC process are also discussed.
Effective optical properties associated with wave propagation in photonic crystals of finite length along the propagation direction92(2002); http://dx.doi.org/10.1063/1.1506390View Description Hide Description
The effective properties associated with the propagation of electromagnetic waves in photonic crystals (PCs) are analyzed for one dimensional photonic crystals to illustrate the difference in those properties between infinitely extended and finite size photonic crystals (along the wave propagation direction). It is shown that the multiple reflections at the two end surfaces of a PC result in oscillations in transmittance, phase velocity, group velocity, as well as effective refractive indexes which are often determined experimentally from the transmitted or reflected wave. At the frequencies far away from the bandgap, the oscillation in both the transmittance and can be modeled by treating the PC as an effective medium with the effective properties derived from the dispersion curves of the corresponding infinitely extended PC. As the frequencies approaching the band edges, however, the oscillations in both transmittance and are markedly enhanced due to the reflections from the internal interfaces in the PC. The results clearly demonstrate the importance of the two end faces on the effective properties of a finite size PC, which can be quite different from those deduced for an infinitely extended PC.
92(2002); http://dx.doi.org/10.1063/1.1509097View Description Hide Description
Waxes and thermopolymers are commonly used to mount optical and photonicmaterials prior to polishing and singularization. After demounting, residual wax/thermopolymer can adhere to the component surface, frequently in the form of particles. Dry, ultraviolet-pulsed laser cleaning has been demonstrated to effectively remove paraffin wax particles, prepared on a glasssurface using a wax aerosol technique. This method produces dome-shaped particles. Experimental evidence suggests the dome-shaped particles are vaporized by the absorption of the energy from the laser pulse. A theoretical model based on vaporization has been developed and this leads to predictions of the critical fluence for single laser pulse removal of dome-shaped particles which is in good agreement with that experimentally measured The model also gives insight into the geometries and relative thermal properties of the “particles” and surface, which are important in determining whether removal by vaporization is a viable process.
92(2002); http://dx.doi.org/10.1063/1.1509110View Description Hide Description
Light shifts induced in the electronic and shallow on-center donor states in spherical semiconductorquantum dots, including magnetic fieldeffects, are theoretically investigated. The interaction of light with the spherical GaAs–(Ga, Al)As quantum dot is treated within a dressed-band approach in which the Kane band structure scheme is used to model the GaAs bulk semiconductor whereas the dressing by the laser field is treated through the renormalization of the GaAs energy gap and conduction/valence effective masses. This nonperturbative approach is valid far from resonances and has been successfully adopted for other confined semiconductor heterostructures. The discrete nature of the electronic and impurity states, characteristic of quantum dot systems, and the possibility of adding extra confining effects by laser and applied magnetic fields opens up a promising route of applicability and/or manipulation of quantum-dot states in recent quantum-computer proposals.