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1 May 2012

Volume 111, Issue 9, Articles (09xxxx)

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J. Appl. Phys. 111, 093103 (2012); http://dx.doi.org/10.1063/1.4709385 (8 pages)

Ani Khachatrian, Joseph S. Melinger, and Syed B. Qadri
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back to top Lasers, Optics, and Optoelectronics

Surface enhanced fluorescence on three dimensional silver nanostructure substrate

Jun Dong, Shixian Qu, Zhenglong Zhang, Meicen Liu, Gaining Liu, Xiaoqing Yan, and Hairong Zheng

J. Appl. Phys. 111, 093101 (2012); http://dx.doi.org/10.1063/1.4709442 (4 pages) | Cited 5 times

Online Publication Date: 2 May 2012

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Multi-dimensional metallic nanostructures were fabricated by self-assembling silver nanoparticles on 3-aminopropyltrimethoxysilane-modified glass substrate and using p-aminothiophenol molecule as a linker. Surface enhanced fluorescence was investigated for Rhodamine 6G fluorophore molecules on the prepared 2D and 3D substrates. The experimental observation showed that the 3D nanostructured substrate presented stronger fluorescence enhancement, comparing with what was observed on the 2D nanoparticle arrays. Higher intensity of local electric field and stronger coupling of surface plasmon resonance in 3D silver nanostructure enhanced the excitation and emission of fluorophore molecules more effectively, leading to a stronger fluorescence enhancement on 3D nanostructured substrate. The result suggests that a metallic substrate with 3D nanostructures can produce better fluorescence enhancement, which is important for studying the mechanism and expanding the potential applications of enhanced fluorescence effect.
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78.55.Hx Other solid inorganic materials
61.46.Df Structure of nanocrystals and nanoparticles ("colloidal" quantum dots but not gate-isolated embedded quantum dots)
78.67.Bf Nanocrystals, nanoparticles, and nanoclusters
73.20.Mf Collective excitations (including excitons, polarons, plasmons and other charge-density excitations)
78.68.+m Optical properties of surfaces
81.16.Dn Self-assembly

High-aspect-ratio grooves fabricated in silicon by a single pass of femtosecond laser pulses

Yuncan Ma (马云灿), Haitao Shi (史海涛), Jinhai Si (司金海), Hai Ren (任海), Tao Chen (陈涛), Feng Chen (陈烽), and Xun Hou (侯洵)

J. Appl. Phys. 111, 093102 (2012); http://dx.doi.org/10.1063/1.4709726 (4 pages) | Cited 1 time

Online Publication Date: 2 May 2012

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High-aspect-ratio grooves have been fabricated in silicon by a single pass of femtosecond laser pulses in water and ambient air. Scanning electron microscopy and energy dispersive x-ray spectroscopy were employed to image for the morphology of the photoinduced grooves and analyze the chemical composition in the surrounding of the grooves. It was observed that the sidewall of the grooves fabricated in water was much smoother than that in ambient air, and there were homogeneous nano-scale protrusions on the sidewall of the grooves fabricated in water. Meanwhile, oxygen species, which was incorporated into the grooves fabricated in air, was not observed in those in water.
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81.16.-c Methods of micro- and nanofabrication and processing
82.53.Mj Femtosecond probing of semiconductor nanostructures
82.80.Ej X-ray, Mössbauer, and other γ-ray spectroscopic analysis methods
68.35.bg Semiconductors
68.47.Fg Semiconductor surfaces
79.20.Ds Laser-beam impact phenomena
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Waveguide terahertz time-domain spectroscopy of ammonium nitrate polycrystalline films

Ani Khachatrian, Joseph S. Melinger, and Syed B. Qadri

J. Appl. Phys. 111, 093103 (2012); http://dx.doi.org/10.1063/1.4709385 (8 pages)

Online Publication Date: 3 May 2012

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We report temperature-dependent measurements of the terahertz (THz) vibrational spectrum of ammonium nitrate (AN) films and mixed potassium nitrate (KN)–ammonium nitrate films using waveguide THz time domain spectroscopy. The experiments were performed on polycrystalline films on the metal surface of a parallel plate waveguide. At cryogenic temperature and with frequency resolution as high as 7 GHz, our measurements produce a complex vibrational spectrum for AN, and show vibrational resonances not observed in previous far infrared and Raman measurements. We investigate potential interactions between AN and the metal surface by measuring THz spectra of films on aluminum, gold, and a gold surface coated with an organic self-assembled monolayer. Measurements are also performed on a deuterated AN film and indicate that the observed THz modes are due largely to the motion of the nitrate ions in the AN crystal. Finally, the effect of introducing small amounts of an impurity into the AN lattice is examined. We find that introduction of as little as 1%-2% by weight of potassium nitrate into the AN lattice causes line broadening of the THz modes, which is consistent with increased disorder introduced by the impurity.
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78.70.Gq Microwave and radio-frequency interactions
78.66.Nk Insulators
78.30.Hv Other nonmetallic inorganics

Effect of Si-induced defects on 1 µm absorption losses in laser-grade YAG ceramics

R. Gaume, Y. He, A. Markosyan, and R. L. Byer

J. Appl. Phys. 111, 093104 (2012); http://dx.doi.org/10.1063/1.4709756 (5 pages)

Online Publication Date: 3 May 2012

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High sensitivity optical absorption at 1 µm was measured in 40 undoped and Nd-doped Y3Al5O12 (YAG) transparent ceramics and single crystals using photothermal common-path interferometry. Concurrently, chemical trace analysis was performed on those samples by glow discharge mass-spectroscopy. Silicon and calcium were found to be the major impurities with concentrations up to 250 wt. ppm. A univocal linear correlation between the Si content and the absorption loss at 1 µm is revealed and a possible mechanism for the formation of Si-induced color centers based on a bound polaron model is discussed. Solutions to reduce this optical absorption in ceramics are also proposed.
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42.70.Hj Laser materials
71.38.-k Polarons and electron-phonon interactions
78.20.Ci Optical constants (including refractive index, complex dielectric constant, absorption, reflection and transmission coefficients, emissivity)
61.72.jn Color centers
78.20.nb Photothermal effects

Transfer printing and nanomanipulating luminescent photonic crystal membrane nanocavities

Bowen Wang, Timothy Siahaan, Mehmet A. Dündar, Richard Nötzel, Sailing He, and Rob W. van der Heijden

J. Appl. Phys. 111, 093105 (2012); http://dx.doi.org/10.1063/1.4712410 (5 pages)

Online Publication Date: 4 May 2012

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The release of photoluminescent InGaAsP photonic crystal nanocavity chiplets from the host chip for creating autonomous functional microparticles is demonstrated. A transfer printing method using a soft polymeric material as a stamp is used to transfer cavity arrays to other substrates. Alternatively, cavities are transferred individually by a nanomanipulation technique. The chiplets can be fully deterministically positioned on both the host chip and another substrate (glass) with the nanomanipulator. The chiplets have the striking property of spontaneously orienting themselves with their plane perpendicular to the receiving surface. At each stage of the process, the condition of the cavities as dependent on their immediate surroundings is monitored from their photoluminescence spectrum.
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42.70.Qs Photonic bandgap materials
78.55.-m Photoluminescence, properties and materials

Strong nonlinear growth of energy coupling during laser irradiation of transparent dielectrics and its significance for laser induced damage

Guillaume Duchateau, Michael D. Feit, and Stavros G. Demos

J. Appl. Phys. 111, 093106 (2012); http://dx.doi.org/10.1063/1.4707755 (12 pages) | Cited 4 times

Online Publication Date: 4 May 2012

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The interaction of high power nanosecond laser pulses with absorbing defects, located in the bulk of transparent dielectric materials and having a multilevel electronic structure, is addressed. The model assumes a moderate localized initial absorption that is strongly enhanced during the laser pulse via excited state absorption and thermally driven generation of new point defects in surrounding material. This model is applied to laser induced damage initiation in the bulk of potassium dihydrogen phosphate crystals (KH2PO4 or KDP) and addresses how during a fraction of the pulse duration the host material around the defect cluster is transformed into a strong absorber that leads to the sufficiently large energy coupling resulting in a damage event. This scenario is supported by time resolved imaging of material modification during the initial phases of laser induced damage in KDP and fused silica.
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79.20.Ds Laser-beam impact phenomena
68.35.Dv Composition, segregation; defects and impurities
71.55.Ht Other nonmetals
73.20.At Surface states, band structure, electron density of states

Nonreciprocal light transmission in silicon by Raman-induced asymmetry of the permittivity tensor

Michael Krause

J. Appl. Phys. 111, 093107 (2012); http://dx.doi.org/10.1063/1.4709622 (4 pages)

Online Publication Date: 4 May 2012

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We consider the effect of Raman-induced nonreciprocal light transmission in silicon and show that it can be understood as the consequence of the asymmetry of an effective permittivity tensor at the Stokes wavelength. This viewpoint enables the derivation of a necessary condition for this effect: the pumping electric field must have components along two different crystallographic axes which are oscillating out of phase with respect to each other.
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78.30.Am Elemental semiconductors and insulators

High efficient antireflective down-conversion Y2O3:Bi,Yb films with pyramid preferred oriented nano-structure

Ming-Hao Qu, Ru-Zhi Wang, Ying Zhang, Kai-Yu Li, and Hui Yan

J. Appl. Phys. 111, 093108 (2012); http://dx.doi.org/10.1063/1.4712461 (5 pages) | Cited 2 times

Online Publication Date: 8 May 2012

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The high efficient antireflective down-conversion Y2O3:Bi,Yb films with nano-structure pyramids were grown successfully on Si (100) substrates using the pulsed laser deposition (PLD). The films microstructure can be controllably tuned only by changing the oxygen pressure in PLD process. With the increasing of the oxygen pressure, the surface morphology changes from smooth surface to pyramid nano-structure, and the preferential orientation of films changes from (222) to (400). Besides, the average reflectance of the films decreases first and then increases, giving a minimum value of 15.8% at 5 Pa as the oxygen pressure increases, which is comparable to that of uniform pyramidal micro-textured surfaces with an average reflectance of 13%–15% fabricated by the complicated chemical etching method. Moreover, upon excitation of ultraviolet photon varying from 300 to 400 nm, near infrared emission of Yb3+ due to transition of the 2F5/2→2F7/2 was observed for all samples, which can be efficiently absorbed by silicon solar cell. These pyramid nano-structure down-conversion Y2O3:Bi,Yb films possess promising applications in enhancement of energy efficiency for crystalline Si solar cells by light trapping and spectrum shifting.
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81.16.Mk Laser-assisted deposition
81.65.Cf Surface cleaning, etching, patterning
68.55.A- Nucleation and growth
61.46.-w Structure of nanoscale materials
78.30.Hv Other nonmetallic inorganics
78.66.Nk Insulators

Thickness dependence of the amplified spontaneous emission threshold and operational stability in poly(9,9-dioctylfluorene) active waveguides

M. Anni, A. Perulli, and G. Monti

J. Appl. Phys. 111, 093109 (2012); http://dx.doi.org/10.1063/1.4711993 (5 pages) | Cited 2 times

Online Publication Date: 9 May 2012

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We investigate the thickness dependence of the amplified spontaneous emission (ASE) threshold and operational lifetime in air-poly(9,9-dioctylfluorene)(PF8)-glass asymmetric active waveguides. We show that the ASE threshold decreases with the film thickness up to about 200 nm, and increases for higher thicknesses. The ASE operational lifetime increases with the thickness up to about 300 nm, and it is almost thickness independent for higher thickness. We show that the observed results are related to the guided mode confinement in the waveguide and to the spatial overlap between the guided modes and the excited region in the film.
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42.79.Gn Optical waveguides and couplers
42.50.Nn Quantum optical phenomena in absorbing, amplifying, dispersive and conducting media; cooperative phenomena in quantum optical systems

Efficiency degradation behaviors of current/thermal co-stressed GaN-based blue light emitting diodes with vertical-structure

Lilin Liu, Minjie Ling, Jianfu Yang, Wang Xiong, Weiqing Jia, and Gang Wang

J. Appl. Phys. 111, 093110 (2012); http://dx.doi.org/10.1063/1.4712030 (9 pages) | Cited 3 times

Online Publication Date: 10 May 2012

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With this work, we demonstrate a three-stage degradation behavior of GaN based LED chips under current/thermal co-stressing. The three stages in sequence are the initial improvement stage, the platform stage, and the rapid degradation stage, indicating that current/thermal co-stressing activates positive effects and negative ones simultaneously, and the dominant degradation mechanisms evolve with aging time. Degradation mechanisms are discussed. Electric current stress has dual characters: damaging the active layers by generating defects and at the same time improving the p-type conductivity by activating the Mg-dopant. High temperature stresses will promote the effects from electric current stresses. The activation of the Mg-dopant will saturate, whereas the generation of defects is carried on in a progressive way. Other mechanisms, such as deterioration of ohmic contacts, also operate. These mechanisms compete/cooperate with each other and evolve with aging time, resulting in the observed three-stage degradation behavior. There exist risks to predict the lifetime of LEDs by a model with a constant accelerated factor.
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85.60.Jb Light-emitting devices

Visual and quantitative measurement of the temperature distribution of heat conduction process in glass based on digital holographic interferometry

Qian Wang, Jianlin Zhao, Xiangyang Jiao, Jianglei Di, and Hongzhen Jiang

J. Appl. Phys. 111, 093111 (2012); http://dx.doi.org/10.1063/1.4712318 (5 pages) | Cited 1 time

Online Publication Date: 10 May 2012

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multimedia

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The temperature distribution of heat conduction process in transparent solid medium is visually and quantitatively measured based on digital holographic interferometry. A series of phase maps reflecting the temperature distribution of a glass sample during the heat conduction process are numerically reconstructed from the digital holograms. Then, based on the derived relationship between temperature variation and phase change, we obtained the full field temperature distribution of the glass sample by the method of sample point calibration. By seriating maps of the temperature distribution, a movie is produced to show the heat conduction phenomenon more vividly. What is more, based on the thermodynamic model of heat conduction, we numerically figured out the temperature distribution of the glass sample using the finite element algorithm. It turns out that the experimental results are consistent with the numerical simulation results very well.
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44.10.+i Heat conduction
05.70.-a Thermodynamics
42.40.Kw Holographic interferometry; other holographic techniques
02.70.Dh Finite-element and Galerkin methods

First-principle description for the high-harmonic generation in a diamond by intense short laser pulse

T. Otobe

J. Appl. Phys. 111, 093112 (2012); http://dx.doi.org/10.1063/1.4716192 (7 pages)

Online Publication Date: 14 May 2012

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We present a first-principles description for the electron excitation and the high-harmonic generation (HHG) in a diamond by intense laser pulse irradiation and their laser parameter dependence. Above band gap harmonics are generated after the peak of the incident laser pulse and have duration much shorter than the laser pulse. The intensity of individual harmonic peaks increases as laser intensity increases nonlinearly, and we find the blue shift of the HHG spectrum when the optical breakdown occurs.
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42.65.Ky Frequency conversion; harmonic generation, including higher-order harmonic generation
42.65.Re Ultrafast processes; optical pulse generation and pulse compression
42.60.-v Laser optical systems: design and operation

Heating dynamics of CO2-laser irradiated silica particles with evaporative shrinking: Measurements and modeling

S. Elhadj, S. R. Qiu, A. M. Monterrosa, and C. J. Stolz

J. Appl. Phys. 111, 093113 (2012); http://dx.doi.org/10.1063/1.4716016 (5 pages) | Cited 1 time

Online Publication Date: 15 May 2012

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The heating dynamics of CO2-laser heated micron-sized particles were determined for temperatures <3500 K measured using infrared imaging. A coupled mass and energy conservation model is derived to predict single particle temperatures and sizes, which were compared with data from particles deposited on non-absorbing substrates to assess the relevant heat transfer processes. Analysis reveals substrate conduction dominates all other heat losses, while laser absorption determined from Mie theory is strongly modulated by particle evaporative shrinking. This study provides insights into the light coupling and heating of particle arrays where the material optical properties are temperature-dependent and particle size changes are significant.
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61.80.Ba Ultraviolet, visible, and infrared radiation effects (including laser radiation)
61.82.Ms Insulators
78.20.Ci Optical constants (including refractive index, complex dielectric constant, absorption, reflection and transmission coefficients, emissivity)
81.40.Gh Other heat and thermomechanical treatments
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