Numerical Design of Composite Pulses for Polycrystalline Samples in Pulsed NQR Spectroscopy

Abstract The density matrix approach along with fictitious spin-1/2 or tensor operator formalisms were employed to obtain general expressions for <Ix>and thus the signal induced in a coil in the case of physically equivalent non-interacting spin I = 1 and 3/2 nuclei in a single crystal with a three-pulse composite pulse. The corresponding powder averages were then obtained and the dependence of the signal on the i-th pulse flip angle (θi) and phase (ϕi) studied. A numerical procedure established the optimum "π/2" composite pulse for polycrystalline samples as (90)0 -(70)45 -(20)25 , where the quantity in parentheses denotes the flip angle and the subscript the phase. A two-pulse composite pulse of the form (126)0 -(300)80 was also inferred, but the three-pulse composite pulse is superior. These composite pulses are shown to have general validity for other spin I values.

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Few-Particle Effects in Nonlinear Optical Spectra of Semiconductor Quantum Dots

MRS Proceedings ◽

10.1557/proc-571-241 ◽

1999 ◽

Vol 571 ◽

Author(s):

Ulrich Hohenesteri ◽

Fausto Rossi ◽

Elisa Molinari

Keyword(s):

Quantum Dots ◽

Density Matrix ◽

Nonlinear Optical ◽

Coherent Control ◽

Optical Spectra ◽

Carrier Dynamics ◽

Semiconductor Quantum Dots ◽

Nonequilibrium Carrier ◽

Optical Nonlinearities ◽

Matrix Approach

ABSTRACTWe present a density-matrix approach for the description of nonequilibrium carrier dynamics in optically excited semiconductor quantum dots, that explicitly accounts for exciton-exciton as well as exciton-carrier interactions. Within this framework, we analyze few-particle effects in the optical spectra and provide a consistent description of additional peaks appearing at high photoexcitation density. We discuss possible applications of such optical nonlinearities in future coherent-control experiments.

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Measurements of Beam Shape Coefficients in Generalized Lorenz-Mie Theory and the Density-Matrix Approach. Part 2: The Density-Matrix Approach

Particle & Particle Systems Characterization ◽

10.1002/ppsc.199700017 ◽

1997 ◽

Vol 14 (2) ◽

pp. 88-92 ◽

Cited By ~ 6

Author(s):

Gérard Gouesbet

Keyword(s):

Density Matrix ◽

Mie Theory ◽

Matrix Approach ◽

Beam Shape

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Optical properties of Quantum Disks: Real density matrix approach

Open Physics ◽

10.2478/s11534-006-0011-4 ◽

2006 ◽

Vol 4 (2) ◽

Cited By ~ 3

Author(s):

Gerard Czajkowski ◽

Leonardo Silvestri

Keyword(s):

Density Matrix ◽

Guided Wave ◽

Matrix Approach ◽

Electron Hole ◽

Optical Functions ◽

Quantum Disk ◽

All Optical ◽

Quantum Disks ◽

Analytical Expressions ◽

Real Density

AbstractWe show how to compute the optical response of a Quantum Disk (QDisk) to an electromagnetic wave as a function of the incident wave polarization, in the energetic region of interband transitions. Both the TM and TE polarization in guided-wave geometry are analyzed. The method uses the microscopic calculation of Quantum Disk eigenfunctions and the macroscopic real density matrix approach to compute the effective QDisk susceptibility, taking into account the valence band structure of the QDisk material and the Coulomb interaction between the electron and the hole. Analytical expressions for the QDisk susceptibility are obtained for a certain model electron — hole potential. Using these expressions, all optical functions can be computed. Results for the absorption coefficient are computed for InAs/GaAs QDisks. Fair agreement with experiments is obtained.

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LINEAR AND NONLINEAR INTERSUBBAND REFRACTIVE INDEX CHANGES IN WURTZITEAlGaN/GaNDOUBLE QUANTUM WELLS: EFFECTS OF PIEZOELECTRICITY AND SPONTANEOUS POLARIZATION

Surface Review and Letters ◽

10.1142/s0218625x09012226 ◽

2009 ◽

Vol 16 (01) ◽

pp. 11-17

Author(s):

L. ZHANG

Keyword(s):

Refractive Index ◽

Density Matrix ◽

Quantum Wells ◽

Structural Parameters ◽

Matrix Approach ◽

Third Order ◽

Numerical Result ◽

Analytical Formulas ◽

Index Changes ◽

Linear And Nonlinear

Based on the density-matrix approach and iterative treatment, a detailed procedure for the calculation of the linear and nonlinear intersubband refractive index changes (RICs) in wurtzite GaN-based coupling quantum wells (CQWs) is given. The simple analytical formulas for electronic eigenstates and the linear and third-order nonlinear RICs in the systems are also deduced. Numerical result on a typical AlGaN / GaN CQW shows that the linear and nonlinear RICs sensitively depend on the structural parameters of the CQW system as well as the doped fraction of nitride semicondutor.

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