Volume 85, Issue 19, 08 November 2004
- lasers, optics, and optoelectronics
- structural, mechanical, thermodynamic, and optical properties of condensed matter
- electronic transport and semiconductors
- magnetism and superconductivity
- dielectrics and ferroelectricity
- nanoscale science and design
- device physics
- applied biophysics
- interdisciplinary and general physics
Index of content:
Optically active and electrically excitable erbium complexes on silicon are made by wet-chemical synthesis. The single-crystalline Er–Si–O compound is formed by coating a Si(100) substrate with an ∕ethanol solution, followed by rapid thermal oxidation and annealing. Room-temperature Er-related photoluminescence is observed with a peak linewidth as small as . The complexes can be excited directly into the Er intra- states, or indirectly, through photocarriers. Er concentrations as high as are achieved, incorporated in a crystalline lattice with a periodicity. Thermal quenching at room temperature is only a factor 5, and the lifetime at is .
- LASERS, OPTICS, AND OPTOELECTRONICS
Influence of the surface termination to the point imaging by a photonic crystal slab with negative refraction85(2004); http://dx.doi.org/10.1063/1.1814430View Description Hide Description
Point imaging by a photonic crystal slab due to the negative refraction is studied theoretically. By investigating the transfer function of the imaging system, the influence of the surface termination to the imaging quality is analyzed. It is shown that an appropriate surface termination is important for obtaining an image of good quality.
85(2004); http://dx.doi.org/10.1063/1.1815377View Description Hide Description
We report on junction light-emitting diodes fabricated from triple heterostructures. Energy band diagrams of the light-emitting diodestructure incorporating piezoelectric and spontaneous polarization fields were simulated, revealing a strong hole confinement near the interface with a hole sheet density as large as for strained structures. The measured current–voltage characteristics of the triple heterostructure junctions have rectifying characteristics with a turn-on voltage of . Electron-beam-induced current measurements confirmed the presence of a junction located at the interface. Strong optical emission was observed at as expected for excitonic optical transitions in these structures. Experimental spectral dependence of the photocurrent confirmed the excitonic origin of the optical transition at . Light emission was measured up to , providing additional confirmation of the excitonic nature of the optical transitions in the devices.
85(2004); http://dx.doi.org/10.1063/1.1818726View Description Hide Description
To overcome the influence of chromophore absorption and degradation in the ultraviolet spectral range for direct photopatterning of electro-opticdevices, a blue laser writing technique operating at has been used to fabricate electro-opticwaveguides from side-chain disperse red-1 doped photosensitive hybrid sol–gel films. The waveguide has good optical confinement and shows an electro-optic coefficient of about and high temporal stability. The results indicate that the hybrid sol–gel a promising matrix for chromophores, and this technique can find applications in direct patterning of electro-opticdevices from nonlinear chromophores-doped photosensitive materials including sol–gels and polymers.
85(2004); http://dx.doi.org/10.1063/1.1815392View Description Hide Description
We report on a process to design highly ordered monolayers of two-dimensional photonic crystals, made of silicananoparticules, that can be used for the development of organic optical devices. We have used a photopolymerization process to incorporate a dye gain medium into the nanoparticle layers in order to achieve a laser cavity. The high spatial coherence of the deposits allows for single-mode laser emission in the plane of the layer when the light excitation is perpendicular to the plane. Such periodic films should help in reducing the number of layers needed for future electrically pumped distributed feedback lasers.
85(2004); http://dx.doi.org/10.1063/1.1815043View Description Hide Description
quantum dots have been fabricated by the selective growth of GaN micropyramid arrays topped with quantum wells. The spatially, spectrally, and time-resolved emission properties of these structures were measured using cathodoluminescence hyperspectral imaging and low-temperature microphotoluminescencespectroscopy. The presence of InGaNquantum dots was confirmed directly by the observation of sharp peaks in the emission spectrum at the pyramid apices. These luminescence peaks exhibit decay lifetimes of approximately , with linewidths down to (limited by the spectrometer resolution).
85(2004); http://dx.doi.org/10.1063/1.1819511View Description Hide Description
We fabricated dye-doped zirconia channel waveguides using wet or dry etching of quartz substrates followed by sol-gel deposition of the Rhodamine 6G-doped zirconia in the channel. Distributed feedback laser action was generated in the channel waveguides by crossing two nanosecond laser beams at . Maintaining the depth of the active zirconia layer at , narrow linewidth lasing was achieved for rectangular channel waveguides with widths at 5, 6.5, and . Wavelength tuning was achieved from . The output laser mode was identified as the fundamental mode. The dispersion behavior of the laser output was checked by comparing experiments with the predictions of Marcatili’s theory.
85(2004); http://dx.doi.org/10.1063/1.1819983View Description Hide Description
We describe an optically prepared and controlled nematic liquid crystal device, using derivatized methyl red self-assembled monolayers for surface alignment on both of its windows. This material demonstrates both reversible and irreversible photoinduced anisotropy, depending on the availability of oxygen during illumination. One window of the cell was permanently aligned prior to assembly while the other window retained its sensitivity to the orientation of the polarization of a controlling optical beam, leading to either a uniform or twisted state in the nematic cell. The entire management of the cell was thereby achieved without touching the alignment surfaces.
Fabrication of high-efficiency Fresnel-type lenses by pinhole diffraction imaging of sol-gel hybrid materials85(2004); http://dx.doi.org/10.1063/1.1815393View Description Hide Description
Sol-gel hybrid materials containing a large quantity of photoactive molecules exhibited large changes in both refractive index and volume on UV exposure. The materials were used for fabrication of Fresnel-type lenses using a simple method: pinhole diffraction imaging. With this technique, problems associated with the contact method could be overcome and Fresnel-type lenses with good focusing performance could be fabricated easily. Importantly, a high diffraction efficiency approaching 85% could be obtained.
85(2004); http://dx.doi.org/10.1063/1.1815069View Description Hide Description
type-I midinfrared diode lasers emitting continuous wave at at room temperature have been studied under high hydrostaticpressure. When the pressure was increased up to , the threshold current varied from , showing a minimum of close to , and the emission spectra shifted to shorter wavelengths by up to (i.e., from ). This exceptional tuning range could be very useful in tunable diode laserabsorption spectroscopy.
Plasma damage-free deposition of Al cathode on organic light-emitting devices by using mirror shape target sputtering85(2004); http://dx.doi.org/10.1063/1.1815394View Description Hide Description
We report on the fabrication of plasma damage-free organic light-emitting devices (OLEDs) by using a mirror shape target sputtering (MSTS) technique. It is shown that OLEDs with Al cathodedeposited by the MSTS show much lower leakage current at reverse bias of , compared to that ( at ) of OLEDs with Al cathodes grown by conventional dc magnetron sputtering. This indicates that there is no plasma damage, which is caused by the bombardment of energetic particles. This suggests that MSTS could be a useful plasma damage-free and low-temperature deposition technique for both top- and bottom-emitting OLEDs and flexible displays.
Femtosecond coherent anti-Stokes Raman scattering spectroscopy using supercontinuum generated from a photonic crystal fiber85(2004); http://dx.doi.org/10.1063/1.1818741View Description Hide Description
Femtosecond time-resolvedcoherent anti-Stokes Raman scattering(CARS)spectroscopy is demonstrated using a Ti:Sapphire oscillator and a photonic crystal fiber. A spectrally dispersed CARS signal of cyclohexane exhibits well-defined beats with a period of , which agrees well with a frequency difference between the symmetric and antisymmetric -stretching vibrational modes.
85(2004); http://dx.doi.org/10.1063/1.1815061View Description Hide Description
A laser micromanipulation is suitable for manipulation of a microscopic object suspended in the liquid. Here we proposed the synchronized laser micromanipulation (SLM) for the trajectory control of the multiple targets with each designed trajectories independently by the single laser. SLM is different from the existing laser scanning micromanipulation in that we can manipulate multiple targets independently by the single laser by changing discrete laser scanning pattern. Here we show the condition for stable transportation of targets depends on the effect of Brownian motion. Accordingly we can manipulate multiple microbeads stably along with each designed trajectories by the proposed method.
Highly efficient yellow and white organic electroluminescent devices doped with -diphenylnaphthacene85(2004); http://dx.doi.org/10.1063/1.1803911View Description Hide Description
We describe the applications of a sterically-hindered yellow dopant,-diphenylnaphthacene () which, when compared to 5,6,11,12-tetraphenylnaphthacene in either tris(8-hydroxyquinolinato)aluminum or diamine (NPB) as host emitter, shows a 50%–34% increase in luminance efficiency over that of device without significantly affecting its color. In addition, we have incorporated the doped yellow NPB emitter into the two-element white organic light-emitting diodes based on benzene dopedanthracene sky-blue emitter which improved the luminance efficiency by 44% over that of to and at with .
Surfactant-assisted synthesis of Tb(III)-doped cerium phosphate single-crystalline nanorods with enhanced green emission85(2004); http://dx.doi.org/10.1063/1.1818346View Description Hide Description
Strong green emission has been obtained for Tb(III)-doped cerium phosphate single-crystalline nanorods synthesized via a facile, Pluronic P123 (, Aldrich)-assisted, hydrothermal method. The surfactant Pluronic P123 was found to play a crucial role in the enhanced photoluminescence emission as compared with the same material but synthesized without the surfactant. The smooth surface, well-defined facets, single crystalline feature, uniform morphologies, and especially very narrow size distributions of the Tb(III)-doped cerium phosphate single-crystalline nanorods are considered to be responsible for the strong photoluminescence emission.
85(2004); http://dx.doi.org/10.1063/1.1814432View Description Hide Description
The temperature performance of type-II semiconductor lasers has been analyzed by comparing the temperature-concentration dependence for a charge-carrier subsystem at the threshold with steady-state temperature-concentration relationship implied by the carrier heating process. The low material gain characteristic of type-II heterostructures and the high resistance of the thermal link to the heat sink are primarily responsible for limiting the continuous-wave laser operation to low temperatures. We show also that the number of cascades for type-II interband cascade lasers can be optimized with respect to the highest achievable operating temperature.
Growth, optical characterization, and laser operation of epitaxial composites with monoclinic structure85(2004); http://dx.doi.org/10.1063/1.1814426View Description Hide Description
Epitaxial monoclinic double tungstate laser crystals were grown with high crystalline quality. Based on these Yb-doped composites, laser operation was demonstrated. Continuous-wave laser emission of a Yb:KYW∕KYW crystal was achieved at . The -thin Yb:KYW layer was pumped at wavelengths near by a Ti:sapphire laser. A maximum output power of was obtained at room temperature.
85(2004); http://dx.doi.org/10.1063/1.1815379View Description Hide Description
We show that the extraordinary transmission of light through an array of square subwavelength holes is strongly influenced by the size of the holes. For small, square holes (air fraction below 20%), the dependence of the normalized transmission (transmissivity) on hole width greatly exceeds the expectations on the basis of conventional aperture theory. For larger holes, the transmissivity saturates. Moreover, the positions of the transmission maxima shift when the size is varied.
85(2004); http://dx.doi.org/10.1063/1.1818729View Description Hide Description
The electromagnetic theory predicts that when a linearly polarized collimated field is focused by a high-angle focusing system, components perpendicular to the initial polarization are generated. The use of annular masks to reduce the area of the focal spot usually increases the magnitude of this phenomenon, known as depolarization. We present a class of masks, the three-ring masks, which are important because they narrow the central lobe of the focal intensity distribution without increasing the depolarization. This can be very useful in modern optical applications, such as confocal microscopy or multiphotonscanning microscopy.
85(2004); http://dx.doi.org/10.1063/1.1818340View Description Hide Description
We investigated bends for photonic crystals with triangular arrays of holes theoretically by employing two-dimensional band-structure and transmission calculations. We find that the guided mode of the bend is frequency-shifted compared with that of a straight waveguide. Decreasing the size of the holes in the immediate vicinity of the bend shifts the frequency of the mode back. These optimized bends can guide light in the frequency region of very low group velocities around corners.
85(2004); http://dx.doi.org/10.1063/1.1810628View Description Hide Description
We present a -doped tellurite glass microsphere laser operating in the band via a cascade process. The microsphere is fabricated by melting the end of a tellurite glass wire, and the microsphere laser is pumped at using a tapered optical fiber. Laser oscillation is observed simultaneously in the band and the band. The threshold of lasing in the band is lower than in the band, and the quantum efficiency in the band increases with pump power above the lasing threshold of the band.