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

1990 ◽  
Vol 45 (3-4) ◽  
pp. 581-586 ◽  
Author(s):  
A. Ramamoorthy ◽  
P. T. Narasimhan

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.

1999 ◽  
Vol 571 ◽  
Author(s):  
Ulrich Hohenesteri ◽  
Fausto Rossi ◽  
Elisa Molinari

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.


Open Physics ◽  
2006 ◽  
Vol 4 (2) ◽  
Author(s):  
Gerard Czajkowski ◽  
Leonardo Silvestri

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.


2009 ◽  
Vol 16 (01) ◽  
pp. 11-17
Author(s):  
L. ZHANG

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.


1989 ◽  
Vol 160 (3) ◽  
pp. 393-399 ◽  
Author(s):  
K. Ruebenbauer ◽  
B. Miczko ◽  
T. Birchall

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