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27 Aug 2012

Volume 101, Issue 9, Articles (09xxxx)

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Appl. Phys. Lett. 101, 091102 (2012); http://dx.doi.org/10.1063/1.4747168 (3 pages)

Hagay Shpaisman, Bhaskar Jyoti Krishnatreya, and David G. Grier
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Lasing in localized mode at optimized photonic amorphous structure

Kwang-Yong Jeong, Yong-Hee Lee, Hui Cao, and Jin-Kyu Yang

Appl. Phys. Lett. 101, 091101 (2012); http://dx.doi.org/10.1063/1.4748109 (4 pages) | Cited 1 time

Online Publication Date: 27 August 2012

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We demonstrated lasing in localized modes of an optimized photonic amorphous structure with short-range order. The InGaAsP multiple quantum wells embedded in a free-standing InGaAsP slab were employed as an active medium by optical pumping at room temperature. The high index contrast between air and InGaAsP, combined with uniformity of local topology and short-range order, enables strong confinement of light via multiple scattering. We confirmed the characteristic of lasing modes in the complex geometry with numerical simulations based on the real images of fabricated samples.
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42.55.Px Semiconductor lasers; laser diodes
42.60.By Design of specific laser systems
42.70.Qs Photonic bandgap materials

Holographic microrefractometer

Hagay Shpaisman, Bhaskar Jyoti Krishnatreya, and David G. Grier

Appl. Phys. Lett. 101, 091102 (2012); http://dx.doi.org/10.1063/1.4747168 (3 pages) | Cited 1 time

Online Publication Date: 27 August 2012

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In-line holographic microscopy of micrometer-scale colloidal spheres yields heterodyne scattering patterns that may be interpreted with Lorenz-Mie theory to obtain precise time-resolved information on the refractive index of the suspending medium. We demonstrate this approach to spatially resolved refractometry with measurements on calibrated refractive index standards and use it to monitor chemical concentration in a microfluidic channel. Using commercially available colloidal spheres as probe particles and a standard video camera for detection yields values for the fluid’s refractive index at the position of each probe particle in each holographic snapshot with a demonstrated resolution of 2×10−3 refractive index units (RIU) and a potential resolution surpassing 10−4 RIU. The combination of spatial resolution, temporal resolution, multi-point in situ access, and technical simplicity recommends this technique for cost-effective lab-on-a-chip applications.
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07.60.Hv Refractometers and reflectometers
07.60.Pb Conventional optical microscopes
42.40.Kw Holographic interferometry; other holographic techniques
82.80.-d Chemical analysis and related physical methods of analysis
85.85.+j Micro- and nano-electromechanical systems (MEMS/NEMS) and devices
07.10.Cm Micromechanical devices and systems

Dual-band terahertz metamaterials based on nested split ring resonators

Sajid Hussain, Jeong Min Woo, and Jae-Hyung Jang

Appl. Phys. Lett. 101, 091103 (2012); http://dx.doi.org/10.1063/1.4748163 (4 pages)

Online Publication Date: 27 August 2012

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Two dual-band terahertz metamaterials based on nested split ring resonators (SRRs) were designed and fabricated on a flexible plastic substrate. Each nested SRR structure composed of two electric field coupled resonators exhibited two transmission minimums, which inherently come from the LC resonances of the respective SRRs. The primary and secondary resonance frequencies can be individually fine-tuned by adjusting the geometry of the respective resonator. The fabricated devices exhibited very low insertion loss of 3 dB in the transmission band and the high attenuation of 27 dB in the stop band.
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84.40.Az Waveguides, transmission lines, striplines

Size and surface effects on transient photoconductivity in CdS nanobelts probed by time-resolved terahertz spectroscopy

Mingjie Li, Bo Wu, Sandy Adhitia Ekahana, Muhammad Iqbal Bakti Utama, Guichuan Xing, Qihua Xiong, Tze Chien Sum, and Xinhai Zhang

Appl. Phys. Lett. 101, 091104 (2012); http://dx.doi.org/10.1063/1.4748300 (5 pages)

Online Publication Date: 27 August 2012

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Ultrafast optical-pump terahertz probe spectroscopy was performed over a graduated size distribution of CdS nanobelts to investigate the size and surface effects on the transient photoconductivity. It was found that the nanobelt size has a profound influence on the carrier localization and photoconductivity dynamics, brought about by the carrier trapping at surface defects. The strong carrier localization in the nanobelt is ascribed to the internal surface boundaries arising from the surface depletion layer. The increased thickness of surface depletion layer due to a continuous trapping of photocarriers at surface defects results in more pronounced carrier localization after photoexcitation.
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73.63.Bd Nanocrystalline materials
78.47.D- Time resolved spectroscopy (>1 psec)
72.40.+w Photoconduction and photovoltaic effects
78.70.Gq Microwave and radio-frequency interactions
72.20.Jv Charge carriers: generation, recombination, lifetime, and trapping
73.25.+i Surface conductivity and carrier phenomena

Control of reflectance and transmittance in scattering and curvilinear hyperbolic metamaterials

T. U. Tumkur, J. K. Kitur, B. Chu, Lei Gu, V. A. Podolskiy, E. E. Narimanov, and M. A. Noginov

Appl. Phys. Lett. 101, 091105 (2012); http://dx.doi.org/10.1063/1.4746387 (4 pages) | Cited 2 times

Online Publication Date: 27 August 2012

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We demonstrate reduced reflectance in curvilinear lamellar hyperbolic metamaterials as well as planar hyperbolic metamaterials consisting of metal/dielectric multilayers, with scatterers deposited on the top. The reduced reflectance is accompanied by a significant enhancement in transmission along with non-reciprocity of transmittance in forward and backward propagating directions. The observed experimental behavior is qualitatively similar to the results of numerical solutions of Maxwell equations. The findings of this study pave the way to a variety of important applications, including broadband enhancement of light trapping in photovoltaic devices.
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81.05.Xj Metamaterials for chiral, bianisotropic and other complex media
42.70.-a Optical materials
42.79.Wc Optical coatings
78.20.Ci Optical constants (including refractive index, complex dielectric constant, absorption, reflection and transmission coefficients, emissivity)
78.67.Pt Multilayers; superlattices; photonic structures; metamaterials

Spontaneous emission control of single quantum dots by electromechanical tuning of a photonic crystal cavity

L. Midolo, F. Pagliano, T. B. Hoang, T. Xia, F. W. M. van Otten, L. H. Li, E. H. Linfield, M. Lermer, S. Höfling, and A. Fiore

Appl. Phys. Lett. 101, 091106 (2012); http://dx.doi.org/10.1063/1.4748302 (4 pages) | Cited 1 time

Online Publication Date: 28 August 2012

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We demonstrate the control of the spontaneous emission rate of single InAs quantum dots embedded in a double-membrane photonic crystal cavity by the electromechanical tuning of the cavity resonance. Controlling the separation between the two membranes with an electrostatic field, we obtain the real-time spectral alignment of the cavity mode to the excitonic line and we observe an enhancement of the spontaneous emission rate at resonance. The cavity has been tuned over 13 nm without shifting the exciton energies. A spontaneous emission enhancement of ≈ 4.5 has been achieved with a coupling efficiency of the dot to the mode β ≈ 92%.
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73.21.La Quantum dots
73.63.Kv Quantum dots
78.67.Hc Quantum dots
71.35.-y Excitons and related phenomena
78.47.jd Time resolved luminescence
42.70.Qs Photonic bandgap materials

Ultralow-power local laser control of the dimer density in alkali-metal vapors through photodesorption

Pankaj K. Jha, Konstantin E. Dorfman, Zhenhuan Yi, Luqi Yuan, Vladimir A. Sautenkov, Yuri V. Rostovtsev, George R. Welch, Aleksei M. Zheltikov, and Marlan O. Scully

Appl. Phys. Lett. 101, 091107 (2012); http://dx.doi.org/10.1063/1.4747537 (4 pages) | Cited 1 time

Online Publication Date: 28 August 2012

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Ultralow-power diode-laser radiation is employed to induce photodesorption of cesium from a partially transparent thin-film cesium adsorbate on a solid surface. Using resonant Raman spectroscopy, we demonstrate that this photodesorption process enables an accurate local optical control of the density of dimer molecules in alkali-metal vapors.
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68.43.Nr Desorption kinetics
61.80.Ba Ultraviolet, visible, and infrared radiation effects (including laser radiation)
68.43.Mn Adsorption kinetics
78.30.Er Solid metals and alloys
78.66.Bz Metals and metallic alloys
82.50.Nd Control of photochemical reactions

Glancing angle Talbot-Lau grating interferometers for phase contrast imaging at high x-ray energy

D. Stutman and M. Finkenthal

Appl. Phys. Lett. 101, 091108 (2012); http://dx.doi.org/10.1063/1.4748882 (5 pages)

Online Publication Date: 28 August 2012

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A Talbot-Lau interferometer is demonstrated using micro-periodic gratings inclined at a glancing angle along the light propagation direction. Due to the increase in the effective thickness of the absorption gratings, the device enables differential phase contrast imaging at high x-ray energy, with improved fringe visibility (contrast). For instance, at 28° glancing angle, we obtain up to ∼35% overall interferometer contrast with a spectrum having ∼43 keV mean energy, suitable for medical applications. In addition, glancing angle interferometers could provide high contrast at energies above 100 keV, enabling industrial and security applications of phase contrast imaging.
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87.85.Pq Biomedical imaging
07.85.-m X- and γ-ray instruments
42.25.Fx Diffraction and scattering
42.79.Dj Gratings
87.59.-e X-ray imaging

Terahertz imaging of inhomogeneous electrodynamics in single-layer graphene embedded in dielectrics

M. J. Paul, J. L. Tomaino, J. W. Kevek, T. DeBorde, Z. J. Thompson, E. D. Minot, and Yun-Shik Lee

Appl. Phys. Lett. 101, 091109 (2012); http://dx.doi.org/10.1063/1.4749280 (3 pages) | Cited 1 time

Online Publication Date: 29 August 2012

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We investigate electron transport properties in large-area, single-layer graphene embedded in dielectric media, using free-space terahertz (THz) imaging and time-domain spectroscopy. Sandwiched between a thin polymethyl methacrylate (PMMA) layer and a Si substrate, graphene layers of different growth recipes exhibit distinctive spatial inhomogeneity of sheet conductivity. The non-contacting, non-destructive THz probe reveals that the PMMA layer induces a small, yet noticeable reduction in conductivity.
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72.80.Vp Electronic transport in graphene
78.70.Gq Microwave and radio-frequency interactions

Low-threshold blue lasing from silk fibroin thin films

Stefano Toffanin, Sunghwan Kim, Susanna Cavallini, Marco Natali, Valentina Benfenati, Jason J. Amsden, David L. Kaplan, Roberto Zamboni, Michele Muccini, and Fiorenzo G. Omenetto

Appl. Phys. Lett. 101, 091110 (2012); http://dx.doi.org/10.1063/1.4748120 (4 pages)

Online Publication Date: 29 August 2012

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Silk is a natural biocompatible material that can be integrated in a variety of photonic systems and optoelectronic devices. The silk replication of patterned substrates with features down to tens of nanometers is exploited to realize highly transparent, mechanically stable, and free-standing structures with optical wavelength size. We demonstrate organic lasing from a blue-emitting stilbene-doped silk film spin-coated onto a one-dimensional distributed feedback grating (DFB). The lasing threshold is lower than that of organic DFB lasers based on the same active dye. These findings pave the way to the development of an optically active biocompatible technological platform based on silk.
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42.55.Mv Dye lasers
42.60.By Design of specific laser systems

Cavity enhanced plasma self-absorption spectroscopy

Anton Walsh, Dongfeng Zhao (赵东锋), and Harold Linnartz

Appl. Phys. Lett. 101, 091111 (2012); http://dx.doi.org/10.1063/1.4748125 (4 pages) | Cited 1 time

Online Publication Date: 29 August 2012

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We introduce cavity enhanced plasma self-absorption spectroscopy (CEpSAS), a sensitive spectroscopic diagnostic tool that is used here for plasma analysis, but can also be used for any light emitting sample. It works without an additional external light source. In CEpSAS, plasma is located in an optically stable cavity consisting of two high reflectivity mirrors, and here it acts both as light source and absorbing medium. We present proof of principle results to illustrate the performance of this technique that literally combines “sense and simplicity.” Quantitative absorption experiments are described on a supersonically expanding hydrocarbon plasma.
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52.70.Kz Optical (ultraviolet, visible, infrared) measurements
07.60.Rd Visible and ultraviolet spectrometers

Simple visible supercontinuum light source with true continuous-wave output power

I. Shavrin, S. Novotny, A. G. Savelyev, S. C. Buchter, and H. Ludvigsen

Appl. Phys. Lett. 101, 091112 (2012); http://dx.doi.org/10.1063/1.4748327 (4 pages) | Cited 1 time

Online Publication Date: 29 August 2012

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We present the concept and both the experimental and computational study of a simple supercontinuum light source emitting at temporally highly stable output powers. The principle of the light source is based on a standard pulsed supercontinuum source combined with fiber-based dispersive time-stretching. This approach allows for tailored spectral emission in the visible at a power stability of below 1%. Furthermore, the computation indicates that highly stable light emission with this concept does not necessarily require highest possible input pulse repetition rates and longest dispersive fiber lengths.
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42.81.Dp Propagation, scattering, and losses; solitons
42.65.-k Nonlinear optics
42.72.-g Optical sources and standards
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Strong reddish-orange light emission from stress-activated Srn+1SnnO3n+1:Sm3+ (n = 1, 2, ∞) with perovskite-related structures

Sunao Kamimura, Hiroshi Yamada, and Chao-Nan Xu

Appl. Phys. Lett. 101, 091113 (2012); http://dx.doi.org/10.1063/1.4749807 (4 pages) | Cited 1 time

Online Publication Date: 30 August 2012

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We report mechanoluminescence (ML) in Sm3+-doped Srn+1SnnO3n+1 (n = 1, 2, ∞) phosphors with perovskite-related structures, which consist of layered units depending on the number of n. The intensity of the ML was strongly dependent on the layered structure; the ML intensity for Sr3Sn2O7:Sm3+ was three orders of magnitude higher than that for SrSnO3:Sm3+. The charge transfer state (CTS) band in the photoluminescence excitation spectra was observed for Sr3Sn2O7:Sm3+ and Sr2SnO4:Sm3+, indicating that the efficient energy transfers from the host to the Sm3+ ions. The formation of CTS and the layered structure may be responsible for this ML enhancement.
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78.60.Mq Sonoluminescence, triboluminescence
71.70.-d Level splitting and interactions
78.55.Hx Other solid inorganic materials

Integrating a plasmonic coupler to photo detector of terahertz frequency

Zhihai Wang, Koji Ishibashi, S. Komiyama, N. Nagai, and K. Hirakawa

Appl. Phys. Lett. 101, 091114 (2012); http://dx.doi.org/10.1063/1.4748581 (3 pages) | Cited 1 time

Online Publication Date: 31 August 2012

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Projection type photo lithography and electroplating techniques were applied to fabricate a plasmonic coupler, and to integrate the coupler on top of a photo detector for terahertz frequency. The coupler is a metallic disk with a sub-wavelength aperture surrounded by concentric gratings. The period and height of the gratings are about 200 μm and 20 μm, respectively. The photo detector is 2-dimensional electron gas in perpendicular magnetic field. The photo signal is change of longitudinal resistance, due to cyclotron absorption of photons. Enhancement of photo signal, due to presence of the plasmonic coupler, was observed.
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42.79.Gn Optical waveguides and couplers
42.82.Et Waveguides, couplers, and arrays
85.60.Gz Photodetectors (including infrared and CCD detectors)
42.79.Dj Gratings
84.40.-x Radiowave and microwave (including millimeter wave) technology
42.82.Cr Fabrication techniques; lithography, pattern transfer

Observation of In-related collective spontaneous emission (superfluorescence) in Cd0.8Zn0.2Te:In crystal

C. R. Ding, Z. L. Li, Z. R. Qiu, Z. C. Feng, and P. Becla

Appl. Phys. Lett. 101, 091115 (2012); http://dx.doi.org/10.1063/1.4748883 (5 pages)

Online Publication Date: 31 August 2012

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The In-related superfluorescence at 788 nm from Cd0.8Zn0.2Te:In single crystal has been observed and characterized by the time-resolved photoluminescence comparing with undoped Cd0.8Zn0.2Te. The peak intensity scales Nc2 and the emitted pulse width scales 1/Nc, where Nc is the coherent excited state population. The detected emission pulse shows delay of 43 ps with respect to the pump pulse and has a pulse width of 60 ps. The observation of superfluorescence from Cd0.8Zn0.2Te:In single crystal extends characteristic studies of CdZnTe as one of materials for making superfluorescence sources.
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78.45.+h Stimulated emission
78.55.Et II-VI semiconductors
61.72.uj III-V and II-VI semiconductors
78.47.jd Time resolved luminescence
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