Volume 90, Issue 17, 23 April 2007
- 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:
The authors report frequency and dissipation scaling laws for doubly clamped diamond resonators. The device lengths range from corresponding to frequency and quality-factor ranges of and 600–2400, respectively. The authors find that the resonance frequency scales as confirming the validity of the thin-beam approximation. The dominant dissipation comes from two sources: for the shorter beams, clamping loss is the dominant dissipation mechanism, while for the longer beams, surface losses provide a significant source of dissipation. The authors compare and contrast these mechanisms with other dissipation mechanisms to describe the data.
- LASERS, OPTICS, AND OPTOELECTRONICS
90(2007); http://dx.doi.org/10.1063/1.2731705View Description Hide Description
A comparative study of cutoff wavelength is performed by photocurrent (PC), transmission, and infrared photoreflectance (PR) spectroscopies on arsenic-doped molecular beam epitaxial layers in the midinfrared spectral region. It is illustrated that (i) a shorter cutoff wavelength of PC response may be predicted by either the band gap or the energy of the half-maximum transmission and (ii) the main PR peak is coincident energetically to that of the third-derivative maximum of the PCspectrum. The mechanism behind is discussed with the aid of photoluminescence measurements. The results indicate that the infrared PR spectroscopy may serve as a contactless alternative to the PCspectroscopy for predicting the cutoff wavelength of narrow-gap HgCdTe epilayers reliably.
Raman intensity enhancement in silicon-on-insulator substrates by laser deflection at atomic force microscopy tips and particles90(2007); http://dx.doi.org/10.1063/1.2730576View Description Hide Description
It is shown that Raman intensities of bulk and film in silicon-on-insulator substrates strongly depend on the incident angle of the exciting laser. In a backscattering geometry with perpendicular laser incidence, deflection at particles or atomic force microscopy tips can thereby lead to a selective enhancement of the film signal, which can be misinterpreted as surface/tip enhanced Raman scattering. The authors report strong enhancement effects by scattering at dielectric particles on silicon-on-insulator and silicon substrates as well as smaller effects for deflection at tips. In evaluating field enhancements on such substrates, this must be considered.
Ultrafast transient photoinduced absorption in silicon nanocrystals: Coupling of oxygen-related states to quantized sublevels90(2007); http://dx.doi.org/10.1063/1.2728756View Description Hide Description
The authors have studied transient photoinduced absorption in single monolayers of oxidizedsiliconnanocrystals. Transient photoinduced absorption measurements along with optical absorption and photoluminescence(PL) emission reveal that the light-absorption process takes place in defects related to strong PL emission, suggesting that the photoexcited carriers are in oxygen-related interface states. They have time-resolved ultrafast relaxation paths in oxygen-related states and quantized sublevels, which have important implications in the understanding of fundamental optical properties for this system.
90(2007); http://dx.doi.org/10.1063/1.2731729View Description Hide Description
The authors demonstrate multiple wavelength lasers fabricated from InGaAsquantum dots. Selective area epitaxy is used to grow the active region, consisting of five layer stack of InGaAsquantum dots with different band gapenergies in selected regions of the substrate, for fabrication of the lasers. The mechanism responsible for engineering of the band gap of quantum dots is discussed. The performance of the selectively grown lasers is compared to the lasers fabricated from structures grown in a standard, nonselective area growth process.
Enhanced spontaneous emission at from colloidal PbSe quantum dots in a Si photonic crystal microcavity90(2007); http://dx.doi.org/10.1063/1.2731657View Description Hide Description
The authors report on the design, fabrication, and characterization of Si-based photonic crystalmicrocavity light emitters utilizing PbSequantum dots. Efficient coupling of emission from PbSequantum dots to Si photonic crystal membrane microcavity is achieved by inserting the quantum dots in a central air hole in the microcavity. Enhancement of spontaneous emission with linewidth of is observed at at room temperature. The Purcell factor and the spontaneous emission coupling factor are estimated to be 35 and 0.04, respectively.
90(2007); http://dx.doi.org/10.1063/1.2731523View Description Hide Description
The authors demonstrate and study two- and three-wavelength generations in the semiconductor diode laser with a tunnel junction separating two different quantum-well active regions integrated within a single waveguide. To avoid resonant cross absorption of the modes at different frequencies and achieve phase matching, the laser waveguide is designed to generate the first-order transverse mode at a longer wavelength and the third-order mode at a shorter wavelength. Excellent agreement with the designed and measured device parameters is observed. Intracavity nonlinear mixing leading to sum-frequency and second-harmonic generation is demonstrated.
90(2007); http://dx.doi.org/10.1063/1.2733601View Description Hide Description
The authors report a technology to make a distributed Bragg reflector laser with buried dielectric grating and band gap tuned reflector region. The Bragg reflector is constructed by high coupling coefficient gratings made of and InP. The band gap of the reflector is blueshifted by self-aligned quantum well intermixing using the buried grating itself. The photoluminescence peak wavelength can be shifted by for the quantum well sample covered by grating compared to thermal shift only at annealing temperature of for . The enhanced interdiffusion is caused by the P vacancies generated at and InP interfaces as proved by secondary ion mass spectroscopy.
90(2007); http://dx.doi.org/10.1063/1.2724894View Description Hide Description
The angular dependence of the reflectivityspectrum for visible light was measured in opal-metal (Ag and W) composites with a high filling factor. The diffraction patterns were observed at a wavelength essentially exceeding the period of a three-dimensional photonic structure. The authors offer a qualitative explanation based on the similarity between the experimental observations and those modified by the three-dimensional periodicity plasmonic effects in two-dimensional periodic structures with a subwavelength defect.
Terahertz continuous-wave large-area traveling-wave photomixers on high-energy low-dose ion-implanted GaAs90(2007); http://dx.doi.org/10.1063/1.2722235View Description Hide Description
Nitrogen ion implantation at and low doses into commercial semi-insulating GaAs is used to manufacture continuously operated metal-semiconductor-metal terahertz photomixer radiation sources based on a traveling-wave interdigitated-finger coplanar stripline structure. The authors systematically investigated the terahertz efficiency over the implantation dose range of and determined the optimum implantation dose range for operation in the frequency range , where a significant higher efficiency is obtained compared to low-temperature-grown GaAs.
90(2007); http://dx.doi.org/10.1063/1.2732832View Description Hide Description
This letter presents a single mode, actively -switched distributed feedback fiber laser. Acoustic pulses are launched into an erbium-doped fiber Bragg grating, resulting in the introduction of a traveling defect. Thus, a transmission peak appears in the reflection band while the pulse travels along the grating. This effect allows the laser to operate in a -switched regime, providing optical pulses which repetition rate was continuously tuned up to . Pulses of of peak power and of temporal width were obtained at low repetition rate.
Tunable few-optical-cycle pulses with passive carrier-envelope phase stabilization from an optical parametric amplifier90(2007); http://dx.doi.org/10.1063/1.2732834View Description Hide Description
The authors report on a scheme for the generation of few-optical-cycle pulses broadly tunable in the visible with passively stabilized carrier-envelope phase (CEP). The system starts with an infrared optical parametric amplifier in which both pump and seed are derived from an amplified, non-CEP-stabilized Ti:sapphire laser. The passively stabilized idler beam is then spectrally broadened through white-light generation and seeds a blue-pumped noncollinear optical parametric amplifier. The system produces few-optical-cycle pulses tunable from , with energy up to and rms CEP fluctuations.
90(2007); http://dx.doi.org/10.1063/1.2732179View Description Hide Description
In integrated circuits, most of the heating is produced in the active layers below the surface, making thermal measurements extremely difficult. The authors demonstrate that near infrared thermoreflectance can provide thermal imaging inside the circuit, through its silicon substrate. The use of an InGaAs camera with a noncoherent illumination in the band allows fast thermal imaging with a diffraction-limited resolution of . A silicon solid immersion lens was then used to further improve the resolution to , corresponding to an effective numerical aperture of 2.36.
90(2007); http://dx.doi.org/10.1063/1.2732202View Description Hide Description
The authors analyze early stages of gradual degradation in highly reliable emitting high-power diode laser arrays with continuous wave emission powers of (facet load of ). In all cases the edges of the metallized emitter stripes are identified as the starting points of gradual degradation. The magnitude of the observed degradation signatures, however, is highly correlated with the bar-specific packaging-induced strain at each emitter. We find a bar-specific effect, namely, the presence of packaging-induced strain, to be the driving force of gradual degradation. Our findings point to the significance of proper strain management in advanced device structures.
Manipulation of tunneling frequencies using magnetic fields for resonant tunneling effects of surface plasmons90(2007); http://dx.doi.org/10.1063/1.2732827View Description Hide Description
This work investigates the manipulation of terahertz surface plasmons (SPs) on a semiconductor surface by applying an external static magnetic field. The dispersion relations of the coupled surface magnetoplasmon under the Voigt configuration in the semiconductor-insulator-semiconductor structure are derived. For a TM-polarized wave that is normally incident onto a semiconductor film with periodic narrow grooves on both surfaces, the applied external static magnetic field with the Voigt configuration redshifts the frequencies of the SP-induced resonant tunneling. This phenomenon is attributable to the reduction in the effective plasma frequency by the applied magnetic field.
90(2007); http://dx.doi.org/10.1063/1.2732835View Description Hide Description
The authors demonstrate a compact and efficient fiber coupling scheme for a surface-emitting photonic crystal laser by using a cleaved fiber tip connected to a wavelength-division-multiplexing fiber coupler. Simultaneous optical excitation and laser light collection are achieved for a InGaAsP graphite-lattice -point band edge laser. On comparing with the conventional microphotoluminescence setup based on an objective lens, their direct butt coupling setup is much simpler and yet offers the fiber-coupled output approximately ten times higher. Finite-difference time-domain simulations confirm that the -point band edge laser exhibits the desired vertical emission property and that the fiber coupling efficiency can be as high as 30%.
Electro-optically tunable second-harmonic-generation gratings in ion-exfoliated thin films of periodically poled lithium niobate90(2007); http://dx.doi.org/10.1063/1.2728739View Description Hide Description
The authors demonstrate that thin, single-crystalfilms fabricated by ion exfoliation of a bulk periodically poled (PPLN) crystal reduced the tuning voltages for electro-optically tunable harmonic generation in PPLN devices. The tuning voltage of resulted in total tuning of the second harmonic signal in the authors’ -thick device, compared to an order of magnitude higher tuning voltage value needed in a comparable bulk device.
90(2007); http://dx.doi.org/10.1063/1.2734388View Description Hide Description
A technique for the generation and detection of phononpolariton was developed based on the near-field heterodyne transient grating method. It features a compact and simple optical setup and easy wavelength tuning ability of the phononpolariton. The wavelength was tuned by changing the grating spacing of a transmission grating positioned in front of a sample, and this was performed by sliding a glass plate with transmission gratings with many different grating spacings along the glass plate surface.
Ambipolar light-emitting organic field-effect transistors using a wide-band-gap blue-emitting small molecule90(2007); http://dx.doi.org/10.1063/1.2734389View Description Hide Description
The authors applied a wide-band-gap molecule of 4,- -bis(styryl)biphenyl (BSBP) as an active layer in light-emitting organic field-effect transistors. They found that BSBP provided both relatively high field-effect hole mobility of and photoluminescence efficiency of 20% in thin film. They achieved ambipolar operation by without breaking vacuum through devices’ preparation and measurements, applying aluminum contacts, and inserting a hydroxyl-free poly(methylmethacrylate) layer, and light emission was observed when the device was operated in the ambipolar mode. The results presented here will open the way to fabricating efficient light-emitting transistors with high mobility.
Direct observation of trapped carriers in polydiacetylene films by optical second harmonic generation90(2007); http://dx.doi.org/10.1063/1.2734469View Description Hide Description
Trapped carriers in polydiacetylene (PDA) films were directly observed by the electric field induced second harmonic generation (EFISHG) using field effect transistor(FET) structure. Response of EFISHG signal from PDA-FET with applying voltage depended strongly on the polarity of gate voltage. For negative bias, which promotes hole injection from source electrode, EFISHG signal was not observed during bias application, whereas it was enhanced after turning off the bias. Electric field formed by trapped holes in PDA activated the EFISHG signal for the negative bias condition.
90(2007); http://dx.doi.org/10.1063/1.2734471View Description Hide Description
The authors have used an electromagnetically induced transparency resonance in rubidium as a dispersive reference to lock the relative frequency of two lasers to the atomic ground-statehyperfine splitting. The beat frequency between the two lasers directly generates a microwave signal at or . High bandwidth feedback was achieved with only low-frequency electronics using the frequency modulation sideband method. The spectral width of the microwave beat frequency was reduced to less than . The technique offers a convenient and low-cost method suitable for many topical two-frequency experiments, including coherent population trapping, slow light, lasing without inversion, and Raman sideband cooling.