Judd-Ofelt analysis of spectra and experimental evaluation of laser performance of Tm3+ doped Lu2SiO5 crystal

This paper reports that the TM3+:Lu2SiO5 (Tm:LSO) crystal is grown by Czochralski technique. The room-temperature absorption spectra of Tm:LSO crystal are measured on a b-cut sample with 4 at.% thulium. According to the obtained Judd-Ofelt intensity parameters Omega(2)=9.3155 x 10(-20) cm(2), Omega(4)=8.4103 x 10(-20) cm(2), Omega(6)=1.5908 x 10(-20) cm(2), the fluorescence lifetime is calculated to be 2.03 ms for F-3(4) -> H-3(6) transition, and the integrated emission cross section is 5.81 x 10(-18) cm(2). Room-temperature laser action near 2 mu m under diode pumping is experimentally evaluated in Tm:LSO. An optical-optical conversion efficiency of 9.1% and a slope efficiency of 16.2% are obtained with continuous-wave maximum output power of 0.67 W. The emission wavelengths of Tm:LSO laser are centred around 2.06 mu m with spectral bandwidth of similar to 13.6 nm.

γ-LiAlO_2上a面ZnO薄膜的光谱特性研究

利用激光脉冲沉积(PLD)技术在(302)γ-LiAlO2衬底上成功生长了非极性的a面(1120)ZnO薄膜,光致发光谱(PL)带边发射峰半峰宽仅为115meV.研究了非极性ZnO薄膜光谱特性的面内各向异性,发现随着入射光偏振方向改变,在偏振透射光谱上,吸收边移动了20meV,这与A、B激子和C激子的能量差一致;而在拉曼光谱上,激发光偏振方向的改变导致E2模式的强度发生明显改变.

利用窄得-奥菲特理论研究Tm:Lu_2SiO_5晶体的光谱特性

采用丘克拉斯基(Czochralski)技术生长了掺铥硅酸镥(Tm∶Lu2SiO5,Tm∶LSO)晶体;测量了LSO晶体在室温下的非偏振吸收光谱和非偏振荧光光谱;利用窄得-奥菲特(Judd-Ofelt)理论计算了Tm∶LSO晶体的窄得-奥菲特强度参数、振子强度、自发辐射概率、辐射寿命、积分吸收截面和积分发射截面.Tm∶LSO晶体的强度参数为Ω2=9.1355×10-20cm2,Ω4=8.4103×10-20cm2,Ω6=1.5908×10-20cm2;Tm∶LSO晶体在1.9μm附近有明显的发射峰(3F4→3H6跃迁),相应的辐射寿命为2.03 ms,积分发射截面为5.81×10-18cm2,半峰全宽(FWHM)为250 nm.用Tm∶LSO晶体在77 K温度下实现了激光运转.利用792 nm的激光二极管(LD)作为抽运源,获得中心波长为1960 nm的激光输出,抽运阈值为2.13 kW/cm2.

Characterization of m-plane ZnO thin film on gamma-LiAlO2 (100) substrate by metal-organic chemical vapor deposition

Non-polar (1 (1) over bar 00)m-plane ZnO thin film has been prepared on gamma-LiAlO2 (100)substrate via the low pressure metal organic chemical vapor deposition. Obvious intensity variation of the E-2 mode in the polarized Raman spectra and the absorption edge shift in the polarized optical transmission spectra indicate that the m-plane film exhibits optical anisotropy, which have applications in certain optical devices, such as the UV modulator and polarization-dependent beam switch. From the atomic force microscopy images, highly-oriented uniform-sized grains of rectangular shape were observed. (c) 2008 Elsevier B.V. All rights reserved.

Light absorption and electrical transport in Si:O alloys for photovoltaics

Thin films (100-500 nm) of the Si:O alloy have been systematically characterized in the optical absorption and electrical transport behavior, by varying the Si content from 43 up to 100 at. %. Magnetron sputtering or plasma enhanced chemical vapor deposition have been used for the Si:O alloy deposition, followed by annealing up to 1250 °C. Boron implantation (30 keV, 3-30× 1014 B/cm2) on selected samples was performed to vary the electrical sheet resistance measured by the four-point collinear probe method. Transmittance and reflectance spectra have been extracted and combined to estimate the absorption spectra and the optical band gap, by means of the Tauc analysis. Raman spectroscopy was also employed to follow the amorphous-crystalline (a-c) transition of the Si domains contained in the Si:O films. The optical absorption and the electrical transport of Si:O films can be continuously and independently modulated by acting on different parameters. The light absorption increases (by one decade) with the Si content in the 43-100 at. % range, determining an optical band gap which can be continuously modulated into the 2.6-1.6 eV range, respectively. The a-c phase transition in Si:O films, causing a significant reduction in the absorption coefficient, occurs at increasing temperatures (from 600 to 1100 °C) as the Si content decreases. The electrical resistivity of Si:O films can be varied among five decades, being essentially dominated by the number of Si grains and by the doping. Si:O alloys with Si content in the 60-90 at. % range (named oxygen rich silicon films), are proved to join an appealing optical gap with a viable conductivity, being a good candidate for increasing the conversion efficiency of thin-film photovoltaic cell. © 2010 American Institute of Physics.

Intersubband optical absorption in quantum dots-in-a-well heterostructures

The theoretical analysis of intersubband optical transitions for InAs/ InGaAs quantum dots-in-a-well ( DWELL ) detectors are performed in the framework of effective-mass envelope- function theory. In contrast to InAs/ GaAs quantum dot (QD) structures, the calculated band structure of DWELL quantitatively confirms that an additional InGaAs quantum well effectively lowers the ground state of InAs QDs relative to the conduction-band edge of GaAs and enhances the confinement of electrons. By changing the doping level, the dominant optical transition can occur either between the bound states in the dots or from the ground state in the dots to bound states in the well, which corresponds to the far-infrared and long-wave infrared (LWIR ) peaks in the absorption spectra, respectively. Our calculated results also show that it is convenient to tailor the operating wavelength in the LWIR atmospheric window ( 8 - 12 mu m ) by adjusting the thickness of the InGaAs layer while keeping the size of the quantum dots fixed. Theoretical predictions agree well with the available experimental data. (c) 2005 American Institute of Physics.

The plasmon resonance absorption of Ag/SiO2 nanocomposite films

The plasmon resonance absorption of the Ag/SiO2 nanocomposite film is investigated. The measured absorption spectra are compared with those calculated by the Mie theory. The results indicate that the Mie theory on the basis of classical electrodynamics can only partially explain the optical absorption spectra of the Ag/SiO2 nanocomposite film. We believe that the plasmon resonance absorption is mainly an intrinsic quality of the metal particle, and can be explained only with the electronic structure of the metal particle. In the latter, surface resonance state is introduced to systematically discuss the optical absorption spectra of the Ag/SiO2 nanocomposite film. (C) 2003 Elsevier Science B.V. All rights reserved.

Fine structure of the plasmon resonance absorption peak of Ag nanoparticles embedded in partially oxidized Si matrix

Ag/Si nanocomposite films were prepared by the radio-frequency magnetron cosputtering method. The fine structure of the plasmon resonance absorption peak was found in film samples. X-ray photoelectron spectroscopy analysis indicated that the samples were composed of a two-layer structure, which accounted for the structure of the optical absorption spectra. The peak located near 445 nm is the plasmon resonance absorption peak of Ag nanoparticles embedded in a partially oxidized Si matrix. Its intensity decreases with decreasing film thickness and disappears in a very thin sample. The peak located near 380 nm originates from the plasmon resonance absorption of the thoroughly oxidized surface layer of the sample. Its intensity does not change with increasing thickness, but it cannot be observed in the very thick sample. (C) 2001 American Institute of Physics.

Interband luminescence and absorption of GaNAs/GaAs single-quantum-well structures

We have investigated the interband electron transitions in a GaNAs/GaAs single quantum well (QW) by photoluminescence and absorption spectra. The experimental results show that the dominant photoluminescence at low temperature and high excitation intensity originates from transitions within the GaNAs layer. The interband transition energy for QWs with different well widths can be well fitted if a type-II band line up of GaNAs/GaAs QWs is assumed. (C) 2000 American Institute of Physics. [S0003-6951(00)03220-4].

Investigation of absorption of nanocrystalline silicon

Nanocrystalline silicon embedded SiO2 matrix is formed by annealing the SiO2 films fabricated by plasma enhanced chemical vapor deposition technique. In conjunction with the micro-Ramam spectra, the absorption spectra of the films have been investigated. The blue-shift of absorption edge with decreasing size of silicon crystallites is due to quantum confinement effect. It is found that nanocrystalline silicon is of an indirect band structure, and that the absorption presents an exponential dependance absorption coefficient on photon energy ii! the range of 2.0-3.0 eV, and a sub-band appears in the the range of 1.0-1.5 eV. We believe that the exponential absorption is due to the indirect band-to-band transition of electrons in silicon nanocrystallites, while the Sub-band absorption is ascribed to transitions between the amorphous silicon states existing in the films.

Kinetic spectra of light-adaptation dark-adaptation and M-intermediate of BR-D96N

BR-D96N is a kind of genetically site-specific mutants of bacteriorhodopsin (BR) with obvious photochromic effect. Compared to the wild type BR, the lifetime of M state of BR-D96N is prolonged to several minutes so that the photochromic kinetics and the intermediates formation can be studied by the conventional spectra analysis. In the experiment, the absorption spectra of the sample at different time after light illumination are measured with spectrophotometer. By fitting and analyzing the variation of the spectra, we suppose that there are three main states in the, photochromic process, i.e., B state (light-adapted state), M state and D state (dark-adapted state). The absorption spectra of the B state, M state and D state are extracted from the experimental data based on this three-state model and the spectra at various time are fitted with the least-square method. So, the variations of population percentages of the M state, B state and D state are obtained and the M state and B state lifetimes are estimated. In another way, from the measurement of the absorption dynamics at 407 and 568 nm, the M state and B state lifetimes are also obtained by two exponential data fitting, which give coincident results with those of the spectra analysis. (C) 2003 Elsevier Science B.V. All rights reserved.

Franz-Keldysh effect and dynamical Franz-Keldysh effect of cylindrical quantum wires

We investigate the interband optical absorption spectra near the band edge of a cylindrical semiconductor quantum wire in the presence of a static electric field and a terahertz electric field polarized along the axis. Optical absorption spectra are nonperturbatively calculated by solving the low-density semiconductor Bloch equations in real space and real time. The influence of the Franz-Keldysh (FK) effect and dynamical FK effect on the absorption spectrum is investigated. To highlight the physics behind the FK effect and dynamical FK effect, the spatiotemporal dynamics of the polarization wave packet are also presented. Under a reasonable static electric field, substantial and tunable absorption oscillations appear above the band gap. A terahertz field, however, will cause the Autler-Townes splitting of the main exciton peak and the emergence of multiphoton replicas. The presented results suggest that semiconductor quantum wires have potential applications in electro-optical devices.

Photochromic kinetic spectra and intermediates of BR-D96N

BR-D96N is a kind of genetically site-specific mutant of bacteriorhodopsin (BR) with obvious photochromic effect. Compared to the wild type BR, the lifetime of M state of BR-D96N is prolonged to several minutes so that the photochromic kinetics and the intermediates formation can be studied by the conventional spectra analysis. In the experiment, the absorption spectra of the sample at different time after light illumination are measured with spectrophotometer. By fitting and analyzing the variation of the spectra, we suppose there-are three main states in the photochromic process, i.e. B state (light-adapted state), M state and D state (dark-adapted state). The absorption spectra of the B state, M state and D state are extracted from the experimental data based on this three-state model and the spectra at various time are fitted With the least square method. So, the variations of population percentages of the M state, B state and D state are obtained and the M state and B state lifetimes are estimated. In another,way, from measuring the absorption dynamics at 407 nm and 568 nm, the M state and B state lifetimes are also obtained by two exponential data fitting, which give coincident results with those of the spectra analysis.

INFLUENCES OF ALLOY DISORDER AND INTERFACE ROUGHNESS ON OPTICAL-SPECTRA OF INGAAS/GAAS STRAINED-LAYER QUANTUM-WELLS

We present studies of alloy composition and layer thickness dependences of excitonic linewidths in InGaAs/GaAs strained-layer quantum wells grown by MBE, using both photoluminescence and optical absorption. It is observed that linewidths of exciton spectra increase with indium content and well size. Using the virtual crystal approximation, the experimental data are analyzed. The results obtained show that the alloy disorder is the dominant mechanism for line broadening at low temperature. In addition, it is found that the absorption spectra related to light hole transitions have varied from a peak to a step-like structure as temperature increases. This behavior can be understood by the indirect space transitions of light holes.

Spectroscopic properties of anisotropic absorption in a neodymium-doped YAlO3 laser crystal

Absorption spectra of YAlO3:Nd for the three crystallographic axes are investigated at room temperature, The spectral strengths indicate that the absorption coefficient of YAlO3:Nd is anisotropic. The anisotropy of the local electric field acting on the rare-earth ion in a laser crystal is considered, An extended Judd-Ofelt theory is applied to calculate the absorption cross sections and oscillator strengths of the electric-dipole transitions in the different principal directions. Three groups of the phenomenological parameters are derived from a least-squares-fitting procedure. We also analyze theoretically the anisotropy of the optical absorption of YAlO3:Nd crystal in detail. (C) 1997 American Institute of Physics.