Volume 85, Issue 14, 04 October 2004
- lasers, optics, and optoelectronics
- plasmas and electrical discharges
- 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:
- LASERS, OPTICS, AND OPTOELECTRONICS
85(2004); http://dx.doi.org/10.1063/1.1795359View Description Hide Description
We achieved the soliton-based miniaturized integration of electro-opticdevices in a photorefractive paraelectric bulk crystal, by driving self-trapping through an external bias field in a top-sided electrode geometry. The ensuing spatially resolved electric field manifests a localized voltage-dependent region in which a quasi-uniform field leads to screening-like self-trapped waves at considerably low voltages without sample miniaturization, along with their electro-optic beam manipulation. By replicating the electrode structure, our achievements constitute the basic building block that paves the way to digitally addressable volume photonic manipulator arrays.
85(2004); http://dx.doi.org/10.1063/1.1795370View Description Hide Description
We experimentally show coupling between two photonic crystal waveguide Bloch modes having a different parity. A monomode ridge waveguideetched in a silicon-on-insulator substrate and connecting to the photonic crystal waveguide allows us to excite the even Bloch mode. Transmission measurements, performed on a broad spectral range, show the even mode propagation along the defect line. Then, spectrally resolved near-field patterns obtained by using a scanning near-field optical microscope in collection mode for wavelengths, inside and outside the multimode region of the photonic crystal waveguide, clearly demonstrate coupling phenomenon between even and odd modes.
85(2004); http://dx.doi.org/10.1063/1.1799243View Description Hide Description
Neodymium-doped strontiumlanthanum aluminate crystals contain two structural centers with slightly different spectroscopic properties, whose proportion is determined by the composition parameter . By choosing a composition with , which grants the dominance of one of these centers (the center ), whose properties are suitable for quasi-three-level laser scheme, efficient continuous-wave laser emission (slope efficiency ) was obtained under Ti:sapphire laser pumping. Preliminary experiments evidence the possibility of obtaining radiation by frequency doubling. Owing to the large absorption linewidth this crystal shows good prospect for diode laserpumping.
85(2004); http://dx.doi.org/10.1063/1.1803617View Description Hide Description
A photoresist microlens is shown to be an extremely efficient reflective element for out-of-plane coupling of light from a negative epoxy-based photoresist (SU8) optical waveguide into a buried siliconphotodetector. Experimentally determined coupling efficiencies are given for integrated waveguide∕photodetector and waveguide∕microlens∕photodetector structures. The highest measured coupling efficiency in a structure with a diameter, high microlens is about 74%, versus an average of about 11% in structures without a microlens. The measured microlens-mediated coupling efficiency is in satisfactory agreement with a simple ray tracing simulation that provides a calculated value of 77.5% for the coupling efficiency.
85(2004); http://dx.doi.org/10.1063/1.1781363View Description Hide Description
In this work, we have studied the temperature dependence of a cholesteric liquid-crystal laser coupled to an optical fiber, with a view towards optical fibersensor applications. To stabilize the laser emission, we developed a procedure to align the liquid crystal placed in the fiber. Unexpected oscillations in the laser emission were observed as the temperature was varied, which can be understood in terms of the competition between bulk and surface anchoring torques.
85(2004); http://dx.doi.org/10.1063/1.1796532View Description Hide Description
The excitation density dependence of the terahertz radiation from a semi-insulating InPsurface was investigated in detail. By changing the excitation density, substantial changes were observed in the wave form with a reversal of the polarity of the radiation field. Different azimuthal angle dependence was also observed for low- and high-density excitations. These facts indicate that three different radiation mechanisms coexist and that the dominant radiation mechanism changes with increasing the excitation density from the drift current, for low-excitation density, to the diffusioncurrent and the optical rectification, for high-excitation density.
85(2004); http://dx.doi.org/10.1063/1.1801166View Description Hide Description
A islands resonant-cavity-enhanced (RCE) detector with high-reflectivity bottom mirror was fabricated by a simple method. The bottom mirror was deposited in the hole formed by anisotropically etching in a basic solution from the back side of the sample with the buried layer in silicon-on-insulator substrate as the etch-stop layer. Reflectivityspectrum indicates that the mirror deposited in the hole has a reflectivity as high as 99% in the range of . The peak responsivity of the RCE detector at is and a full width at half maximum of is obtained. Compared with the conventional photodetector, the responsivity of RCE detector has a nearly threefold enhancement.
85(2004); http://dx.doi.org/10.1063/1.1803937View Description Hide Description
We report an achromatic holographic method to fabricate high-resolution x-ray optics using coherent extreme-ultravioletradiation from an undulator source. The interference pattern between two spherical beams, which are created using Fresnel zone plates, is recorded to produce a higher-resolution zone plate. Analytical and simulation results showing the formation of the zone plate pattern was confirmed experimentally with the production and testing of a lens with outermost zone width. The combination of extreme-ultraviolet light, which exposes photoresists with practically no proximity effect, and holography, which guarantees the accurate placement of zones, addresses the main difficulties faced in the improvement of the resolution of x-raylenses.Holography with extreme-ultraviolet light has the potential to produce lenses with sub- resolution.
85(2004); http://dx.doi.org/10.1063/1.1804252View Description Hide Description
We present a nonlinear modulation scheme based on coupling between optically excited surface plasmons in a thin goldfilm and the heating of the film by a pulsed direct current, and also for the reverse process. The reflected surface-plasmon excitation beam is shown to undergo a spatial deformation as a function of a pulsed current through the foil. Similarly, the current through the thin film is modulated by the action of periodic excitation of surface plasmons using infrared photons.
Temporal and noise characteristics of continuous-wave-pumped continuum generation in holey fibers around85(2004); http://dx.doi.org/10.1063/1.1801175View Description Hide Description
The noise of continuous-wave-pumped broadband continua generated in a holey fiber is characterized in two different all-fiber configurations. An amplified spontaneous emission seeded ytterbium-doped fiber source and fiber Bragg grating based laser were employed to initiate Raman-soliton continuum generation in of anomalously dispersive holey fiber with spectral width of and spectral power density over . Low noise operation makes these sources suitable for optical coherence tomography applications.
Recovering image resolution in reconstructing digital off-axis holograms by Fresnel-transform method85(2004); http://dx.doi.org/10.1063/1.1791735View Description Hide Description
The resolution of amplitude and phase reconstruction of images from digital holograms by the Fresnel transformation method is limited by the pixel width in the reconstructed image plane. The reconstruction pixel depends on distance, wavelength, and number of pixels in the hologram. The spatial frequencies, in the reconstructed image, are band limited by the size of the reconstruction pixel. Undersampling can occur, in the image plane, in the reconstructed amplitude and/or wrapped phase maps. Recovery of reconstructed undersampled spatial frequencies, is possible by the fictitious enlargement of the digital hologram. Correct profile reconstruction of a siliconmicroelectromechanical structure is demonstrated, applying the proposed method.
85(2004); http://dx.doi.org/10.1063/1.1801686View Description Hide Description
Europium was implanted into through a thick epitaxially grown layer that protects the surface during the implantation and also serves as a capping layer during the subsequent furnace annealing. Employing this layer prevents the formation of an amorphous surface layer during the implantation. Furthermore, no dissociation of the crystal was observed by Rutherford backscattering and channeling measurements for annealingtemperatures up to . Remarkably, the intensity of the Eu related luminescence, as measured by cathodoluminescence at room temperature, increases by one order of magnitude within the studied annealing range between 1100 and .
85(2004); http://dx.doi.org/10.1063/1.1797554View Description Hide Description
We have performed measurements on terahertz (THz) apertureless near-field microscopy that show that the temporal shape of the observed near-field signals is approximately proportional to the time-integral of the incident field. Associated with this signal change is a bandwidth reduction by approximately a factor of 3 which is observed using both a near-field detection technique and a far-field detection technique. Using a dipole antenna model, it is shown how the observed effects can be explained by the signal filtering properties of the metal tips used in the experiments.
85(2004); http://dx.doi.org/10.1063/1.1801672View Description Hide Description
We present a rigorous mathematical formulation of the diffraction process in optical systems, provided the aperture stop is much smaller than the remaining components. This mathematical scheme allows us to develop methods for the exact numerical calculation of the complex amplitude for any optical system consisting of lenses and an aperture stop placed at any space (either input, output, or intermediate). The procedure eliminates the need of using the exit pupil for calculations and evidences the practical inaccuracies that may arise due to the use of the exit pupil. We present several results for a meniscus lens working with an aperture stop placed before the lens, so that the comparison between the standard calculation procedures, our methods, and the experiment is clearly illustrated.
85(2004); http://dx.doi.org/10.1063/1.1798394View Description Hide Description
We report experimental results on a high-power, cladding-pumped, heavily co-doped phosphate fiber laser of very short length. Up to cw laser power was obtained from an-long multimode-core active fiber with optimized input and output couplers, when pumped by a diode laser at . The fiber laser was demonstrated at with a linewidth, and a good beam quality of .
Quasistatic electric-field-modulated optical pattern transition in a thin nematic liquid-crystal film with a single feedback mirror85(2004); http://dx.doi.org/10.1063/1.1795363View Description Hide Description
We present here the pattern formation in the transverse profile of a continuous-wave laser beam passing through a parallel planar-aligned nematic liquid crystal(NLC)film biased by a quasistatic electric field and then reflected back to the sample cell by a single planar mirror. The effect of the biasing voltage is studied through the ability to change the nonlinearity by modulating the orientation of the NLC molecules electrically. By suitably modulating the quasistatic electric field the optical pattern transition from the hexagon to the roll is achieved. The pattern transition can be explained by the linear stability analysis for the nonlinear liquid crystalfilm with optical feedback.
85(2004); http://dx.doi.org/10.1063/1.1803623View Description Hide Description
We report the use of extrusion for the development of planar buried channel waveguide lasers in a neodymium-doped lead-silicate glass host. The extrusion process was performed at a constant die temperature of , an applied pressure of and a viscosity of , respectively. A planar substrate, in length cut from the extruded product, had four buried waveguides each with a core size of 8 by in the horizontal and vertical directions. Optical characterization of this waveguide revealed single-mode laser operation at with a slope efficiency of 40% for an absorbed power of . The measured device propagation loss was .
85(2004); http://dx.doi.org/10.1063/1.1801681View Description Hide Description
We show that the wave front of a total internal reflected beam is perturbed by fluctuations in the region probed by the evanescent wave, and light is scattered both above and below the critical angle. While singly scattered light is related to the two-dimensional Fourier transform at the boundary, multiply scattered light originating from very turbid samples can appear only below the critical angle. We show that the very weak scattered light above the critical angle is due to a double tunnel effect, and it is solely due to single scattering at the surface. Applications are discussed.
Semiconductor lasers with an inversely biased active region for generation of millimeter wave modulated signals85(2004); http://dx.doi.org/10.1063/1.1758778View Description Hide Description
A semiconductor laser structure is proposed to introduce field effects in its active region. It has five layers of with four electrical contacts to the doped layers, where the current injection into an inversely biased active region is based on the operation of two complementary bipolar transistors with their base-collector junction common. The inverse bias is useful to incorporate carrier transfer phenomena like Gunn effect in semiconductor lasers. Our analysis on the proposed lasers shows that its lasing operation is possible while applying a high electric field more than V/m in the carrier transfer domain.
- PLASMAS AND ELECTRICAL DISCHARGES
Enhanced generation of fast protons from a polymer-coated metal foil by a femtosecond intense laser field85(2004); http://dx.doi.org/10.1063/1.1803915View Description Hide Description
The results of generation of fast protons from -thick copper foil targets by laser irradiation at are presented. Both polyvinylmethylether (PVME)-coated and uncoated copper foil targets are examined. Fast protons are measured using a Thomson mass spectrometer and maximum proton energies are 570 and for the PVME-coated and the uncoated target, respectively. The intensity of fast protons with energy of from the PVME-coated target is approximately 80-fold higher than that from the uncoated target.