High Power Quantum Cascade Lasers Operating at Room Temperature

M. Razeghi,S. Slivken 한국물리학회 2003 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.42 No.III

In this paper, some key design and technology issues for development of high power quantum cascade lasers are discussed. The scaling of power output with the number of emitting stages is shown. As part of this work, high power, 75-stage, $\lambda$ = 9 $\mu$m lasers have been demonstrated with a peak power of 7 W at room temperature. This power is a direct result of high quality material growth and a low loss waveguide design. Similar results are demonstrated at a shorter wavelength ($\lambda$ = 6.1 $\mu$m) utilizing a strain-balanced active region/injector design. For a 30-stage structure, 2 W peak power and 250 mW average power have been demonstrated at room temperature. Lastly, a timeline comparison of QCL laser performance is presented in terms of room temperature threshold current density and peak output power for various groups.

Experimental Investigation on the Inherent and Initial Induced Anisotropy of Sand

Hamid Reza Razeghi,Hadi Mohamadzadeh Romiani 대한토목학회 2015 KSCE JOURNAL OF CIVIL ENGINEERING Vol.19 No.3

In this paper, an experimental study concerning the relevance of the initial stress state and the inclination of principal effectivestress to vertical (α) on the behavior of sand is presented. The study was carried out using the dry air pluviated Firoozkuh sand in ahollow cylinder apparatus. Most of the specimens were consolidated subjected to the anisotropic initial stress state, which is made bymaintaining the principal stress ratio (i.e., Rc) and the inclination of initial principal stress (i.e., Rc) constant during the consolidationphase. Shear loading was carried out in the drained condition while the value of α and intermediate principal stress ratio (i.e., b) wereheld constant. Sands subjected to the anisotropic vertical initial stress (Rc = 2, αc = 0) are found to be highly influenced by α due toinitial induced anisotropy in addition to inherent anisotropy. The anisotropic response of medium dense sands is observed to bestrongly dependent on αc. The effect of soil anisotropy, specifically initial induced anisotropy, on the shear modulus is morenoticeable than the shear strength. The initial induced anisotropy due to the initial stress state of medium dense sand may have asignificant influence on the deformation of geotechnical structures such as shallow foundations, so that its neglecting may lead tounsafe designs.

Probabilistic Seismic Hazard Analyses and Obtaining Uniform Hazard Spectra of Tabriz, Iran

H. R. Razeghi,G. Ghodrati Amiri,S. A. Razavian Amrei,M. A. Rahimi 대한토목학회 2016 KSCE Journal of Civil Engineering Vol.20 No.5

In this study Probabilistic Seismic Hazard Analysis is carried out for Tabriz region and results are presented by spectral isoacceleration maps and Uniform Hazard Spectra (UHS) for two levels of hazard. To achieve this goal, at first a catalog of all the historical and instrumentally recorded earthquakes covering timeline from 858 up to 2010, in a radius of 200 km around Tabriz city, has been gathered and processed for elimination of the aftershocks and foreshocks from main occurrences list and then seismicity parameters have been obtained by Kijko (2000) method. The seismic sources of the considered region have been studied and modeled. Probabilistic seismic hazard analysis is implemented for 22*17 grid points over Tabriz region and it’s vicinity using SEISRISK III (1987) software by employing four attenuation relationships and two relationships between earthquake maximum magnitude and fault rupture length. The Results are combined using logic tree method and shown by spectral acceleration maps and Uniform Hazard Spectra with 2 and 10% probability of exceedence (PE) in 50 years for two types of soil.

6.5μm에서 동작하는 양자계단 레이저의 특성

유재수,Slivken, S.,Razeghi, M. 경희대학교 레이저공학연구소 2006 레이저공학 Vol.17 No.-

We have investigated the characteristics of quantum cascade lasers operating at λ∼6.5 ㎛. Using a high-reflectivity coating, the peak output power of 925 mW and the average power of 150 mW were obtained. From 298 K to 393 K, the characteristic temperature was 195 K. The laser operated up to 220 K in continuous-wave mode.

MAPS PRESERVING JORDAN AND ⁎-JORDAN TRIPLE PRODUCT ON OPERATOR ⁎-ALGEBRAS

Darvish, Vahid,Nouri, Mojtaba,Razeghi, Mehran,Taghavi, Ali Korean Mathematical Society 2019 대한수학회보 Vol.56 No.2

Let ${\mathcal{A}}$ and ${\mathcal{B}}$ be two operator ${\ast}$-rings such that ${\mathcal{A}}$ is prime. In this paper, we show that if the map ${\Phi}:{\mathcal{A}}{\rightarrow}{\mathcal{B}}$ is bijective and preserves Jordan or ${\ast}$-Jordan triple product, then it is additive. Moreover, if ${\Phi}$ preserves Jordan triple product, we prove the multiplicativity or anti-multiplicativity of ${\Phi}$. Finally, we show that if ${\mathcal{A}}$ and ${\mathcal{B}}$ are two prime operator ${\ast}$-algebras, ${\Psi}:{\mathcal{A}}{\rightarrow}{\mathcal{B}}$ is bijective and preserves ${\ast}$-Jordan triple product, then ${\Psi}$ is a ${\mathbb{C}}$-linear or conjugate ${\mathbb{C}}$-linear ${\ast}$-isomorphism.

MAPS PRESERVING JORDAN TRIPLE PRODUCT A^*B + BA^* ON *-ALGEBRAS

Taghavi, Ali,Nouri, Mojtaba,Razeghi, Mehran,Darvish, Vahid The Kangwon-Kyungki Mathematical Society 2018 한국수학논문집 Vol.26 No.1

Let $\mathcal{A}$ and $\mathcal{B}$ be two prime ${\ast}$-algebras. Let ${\Phi}:\mathcal{A}{\rightarrow}\mathcal{B}$ be a bijective and satisfies $${\Phi}(A{\bullet}B{\bullet}A)={\Phi}(A){\bullet}{\Phi}(B){\bullet}{\Phi}(A)$$, for all $A,B{\in}{\mathcal{A}}$ where $A{\bullet}B=A^{\ast}B+BA^{\ast}$. Then, ${\Phi}$ is additive. Moreover, if ${\Phi}(I)$ is idempotent then we show that ${\Phi}$ is ${\mathbb{R}}$-linear ${\ast}$-isomorphism.

Maps preserving Jordan and $\ast$-Jordan triple product on operator $\ast$-algebras

Vahid Darvish,Mojtaba Nouri,Mehran Razeghi,Ali Taghavi 대한수학회 2019 대한수학회보 Vol.56 No.2

Let $\mathcal{A}$ and $\mathcal{B}$ be two operator $\ast$-rings such that $\mathcal{A}$ is prime. In this paper, we show that if the map $\Phi:\mathcal{A}\to\mathcal{B}$ is bijective and preserves Jordan or $\ast$-Jordan triple product, then it is additive. Moreover, if $\Phi$ preserves Jordan triple product, we prove the multiplicativity or anti-multiplicativity of $\Phi$. Finally, we show that if $\mathcal{A}$ and $\mathcal{B}$ are two prime operator $\ast$-algebras, $\Psi:\mathcal{A}\to\mathcal{B}$ is bijective and preserves $\ast$-Jordan triple product, then $\Psi$ is a $\mathbb{C}$-linear or conjugate $\mathbb{C}$-linear $\ast$-isomorphism.

Injector doping level-dependent continuous-wave operation of InP-based QCLs at λ ∼ 7.3 µm above room temperature

Yu, J S,Slivken, S,Razeghi, M Institute of Physics 2010 Semiconductor science and technology Vol.25 No.12

<P>We report the continuous-wave (CW) operation of InGaAs/InAlAs quantum cascade lasers (QCLs) operating at λ ∼ 7.3 µm above room temperature. The injector doping level-dependent CW characteristics above room temperature are investigated for doping densities between 7 × 10<SUP>16</SUP> cm<SUP>−3</SUP> and 2 × 10<SUP>17</SUP> cm<SUP>−3</SUP>. The device performance, i.e. threshold current density, output power, operating temperature and characteristic temperature, depends strongly on the injector doping density. For a relatively low injector doping density of 7 × 10<SUP>16</SUP> cm<SUP>−3</SUP>, a high-reflectivity-coated 10 µm wide and 4 mm long laser exhibits an improved device performance with an output power of 152 mW and a threshold current density of 1.37 kA cm<SUP>−2</SUP> at 298 K under CW mode, operating up to 343 K. The thermal characteristics are also analyzed by the estimation from the experimentally measured data for the QCLs with different injector doping densities.</P>

Fabrication of GaN nanotubular material using MOCVD with an aluminium oxide membrane

Jung, Woo-Gwang,Jung, Se-Hyuck,Kung, Patrick,Razeghi, Manijeh IOP Pub 2006 Nanotechnology Vol.17 No.1

<P>GaN nanotubular material is fabricated with an aluminium oxide membrane in MOCVD. SEM, XRD, TEM and PL are employed to characterize the fabricated GaN nanotubular material. An aluminium oxide membrane with ordered nanoholes is used as a template. Gallium nitride is deposited at the inner wall of the nanoholes in the aluminium oxide template, and the nanotubular material with high aspect ratio is synthesized using the precursors of TMG and ammonia gas. Optimal synthesis conditions in MOCVD are obtained successfully for the gallium nitride nanotubular material in this research. The diameter of the GaN nanotube fabricated is approximately 200–250?nm and the wall thickness is about 40–50?nm. GaN nanotubular material consists of numerous fine GaN particulates with size range 15–30?nm. The composition of gallium nitride is confirmed to be stoichiometrically 1:1 for Ga and N by EDS. XRD and TEM analyses indicate that the grains in GaN nanotubular material have a nano-crystalline structure. No blue shift is found in the PL spectrum on the GaN nanotubular material fabricated in an aluminium oxide template.</P>

Thermal analysis of buried heterostructure quantum cascade lasers for long-wavelength infrared emission using 2D anisotropic heat-dissipation model

Lee, H. K.,Chung, K. S.,Yu, J. S.,Razeghi, M. WILEY-VCH Verlag 2009 Physica status solidi. PSS. A, Applications and ma Vol.206 No.2

<P>We have theoretically investigated and compared the thermal characteristics of γ ∼ 10.6 μm InGaAs/InAlAs/InP buried heterostructure (BH) quantum cascade lasers (QCLs) with different heat-sinking configurations by a steady-state heat-transfer analysis. The heat-source densities were obtained from laser threshold power densities measured experimentally under room-temperature continuous-wave mode. The two-dimensional anisotropic heat-dissipation model was used to calculate the temperature distribution, heat flux, and thermal conductance (G<SUB>th</SUB>) inside the device. For good thermal characteristics, the QCLs in the long-wavelength infrared region require the relatively narrow BH structure in combination with epilayer-down bonding due to thick active core/cladding layers and high insulator losses. The single-ridge BH structure results in slightly higher thermal conductance by ∼2–4% than the double-channel (DC) ridge BH structure. For W = 12 μm with 5 μm thick electroplated Au, the single-ridge BH laser with epilayer-down bonding exhibited the highest G<SUB>th</SUB> value of 201.9 W/K cm<SUP>2</SUP>, i.e. increased by nearly 36% with respect to the epilayer-up bonded DC ridge waveguide laser. This value is improved by ∼50% and ∼62% with respect to the single-ridge BH laser and DC ridge waveguide laser with W = 20 μm in the epilayer-up bonding scheme, respectively. (© 2009 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)</P>