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استجابة التضمين والضوضاء في قفل الحقن لليزرات التعاقب الكمي == INTENSITY MODULATION RESPONSE AND NOISE IN INJECTION - LOCKING QUANTUM CASCADE LASERS

Author name: اخلاص عبد العالي حسين
Supervisor name: حسين هادي وارد
General topic: Physics
Specific topic: Physics
Degree: Master
University: University of Thi-Qar - College Of Science - Physics Department
Language: English
University location: Dhi Qar
First pages:
Abstract: In communication field, there are many advantages for using terahertz carriers in optical data transmission along both analog and digital links such as small antenna sizes and large information bandwidth. The optical injection locking is an alternative technique to improve the dynamic properties of QCL light sources. In this technique the frequency and phase of one laser oscillator, known as the slave laser, are locked through the direct coupling to the light injection from another laser oscillator, known as the master laser. In this work, the optical injection locking induced laser dynamics in a QCL is investigated theoretically. The present theoretical analyses are based on the rate equations model that takes into account all carrier relaxation processes as well as the effect of the optical injection locking. The small signal analysis is used to calculate the intensity modulation response and intensity noise in QCL. The present analysis focuses on the effect of carrier relaxation time and the optical injection locking on the dynamic properties in these devices. The results show that the optical injection locking and fast carrier relaxation time can enhance the dynamic properties and decreases noise value and increases the modulation bandwidth in these advanced lasers. The optical injection locking increases the carrier density in active region to suppress the effect of fast carrier scattering to lower state and enhances the stimulated emission. The fast carrier relaxation times decreases the threshold injection current. Also, in optical injection operation, the active region length and linewidth enhancement factor has strong effect on the intensity modulation response and intensity noise.

دراسة الخواص المغناطيسية لنظام فيريمغناطيسي ذي برم مختلط باستخدام تقريب متوسط المجال == Study of the Magnetic Properties of a Mixed Spin Ferrimagnetic System by Using Mean Field Approximation

Author name: اسماء مزعل جاسم
Supervisor name: حسن عبد ياسر | هادي قاسم محمد
General topic: Physics
Specific topic: Physics
Degree: Master
University: University of Thi-Qar - College Of Science - Physics Department
Language: Arabic
University location: Dhi Qar
First pages:
Abstract: In this research it has been investigated the magnetic properties of a mixed spin - 2 and spin - 7/2 lsing binary ferrimagnetic system which is numerically solved by using the mean - field approximation (MFA), for a square lattice and simple cubic one; respectively.The magneto crystalline anisotropies have carefully been changed so as to investigate an interesting phenomenon which is called “Compensation phenomenon” where it has been found that the mixedspin Ising system which is considered has one compensation temperature and ) 4z ( square for a 85 . 2 1 . 3     B D , 85 . 1 1 . 2     B D when the considered system , respectively. Whereas lattice ) 6z ( simple cubic A atoms of for the sublattice anisotropies compensation points multi has in the range  7.1  DA  6.1, 10.4  DA  9.2 for a square and simple cubic lattice, respectively. Besides that it has been studied this phenomenon in the presence of an external magnetic field. We have , 1 . 0 2 . 0     H , , i.e. H lues of t a certain range of negative va found tha gives rise to the multi compensation points. On the other hand, the obtained results indicate that the considered system has experienced first - order and second - order phase transitions, in the planes mA,T , mB ,T respectively. At certain values of sublattices observe that the ordered , one can H , in the absence of A D anisotropies may show the first order phase transition rom the  phases at T  0K SA  2 state to the SB  7 / 2 state, when the value of anisotropyDB decreases.As well, we have examined the phase transitions within the calculation of the free energy function on the basis of Bogoliubov inequality in the plane  f ,T  to obtain precisely results compared of both crystalline for ) TM, ( se ones have been shown in the plane tho sublattices. Our results are encouraged and helpful to support and clarify the characteristic features in a series bimetallic molecularbased magnets. Besides that these magnetic materials have applications in the area of thermo - magneto recording.

دراسة نظرية لعملية انتقال الالكترون خلال بعض التراكيب النانوية == Theoretical Study of Electron Transport Through Some Nanoelectronic Structures

Author name: محمد عبد الامير عباس
Supervisor name: فلاح حسن حنون | لافي فرج البدري
General topic: Physics
Specific topic: Physics
Degree: Master
University: University of Thi-Qar - College Of Science - Physics Department
Language: English
University location: Dhi Qar
First pages:
Abstract: The present work is a theoretical study for the electronic properties of the electron transport process throughout some molecular structures. The investigated system is a left lead - donor - molecule - acceptor - right lead. The investigate molecule is one of the following structures (Phenyl, Biphenyl, Triphenyl, Naphthalene, Anthracene and Phenanthrene).A theoretical treatment of steady - state has been presented to express the transmission probability of the electron transport throughout ring structures. The Hamiltonian describing the system is the Anderson - Newns Hamiltonian with neglecting the spin and Coulomb interactions on the system. The treatment easily includes a magnetic flux effect on the transport process for any ring structure. Furthermore, the most important effects, taking into consideration, are quantum interference, gate voltage and bias voltage. The transmission probability is employed to calculate the conductance and electric current.Density functional theory (DFT) has also been used to calculate electronic properties of considered molecules, especially on the energy - band gap and density of states, and the distribution of electronic density (HOMO and LUMO). It has been ensured that all studied systems simulated using Caussian program 09 can be fabricated by utilizing their computed total energy.The quantum interference effect at typical values of magnetic flux was utilized to design quantum logic gates (XNOR gate and NAND gate) and nanoscale rectifier (half - wave rectifier and full - wave rectifier).
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