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Rahachou, Aliaksandr
Alternative names
Publications (10 of 11) Show all publications
Rahachou, A. & Zozoulenko, I. V. (2007). Light propagation in nanorod arrays. Journal of optics. A: Pure and applied optics, 9(3), 265-270
Open this publication in new window or tab >>Light propagation in nanorod arrays
2007 (English)In: Journal of optics. A: Pure and applied optics, ISSN 1464-4258, Vol. 9, no 3, p. 265-270Article in journal (Refereed) Published
Abstract [en]

We study the propagation of TM- and TE-polarized light in two-dimensional arrays of silver nanorods of various diameters in a gelatin background. We calculate the transmittance, reflectance and absorption of arranged and disordered nanorod arrays and compare the exact numerical results with the predictions of the Maxwell–Garnett effective-medium theory. We show that interactions between nanorods, multipole contributions and formations of photonic gaps affect strongly the transmittance spectra that cannot be accounted for in terms of the conventional effective-medium theory. We also demonstrate and explain the degradation of the transmittance in arrays with randomly located rods as well as the weak influence of their fluctuating diameter. For TM modes we outline the importance of the skin effect, which causes the full reflection of the incoming light. We then illustrate the possibility of using periodic arrays of nanorods as high-quality polarizers.

Keywords
nanorods, particle plasmons, Maxwell–Garnett theory, Green's function technique
National Category
Engineering and Technology
Identifiers
urn:nbn:se:liu:diva-14620 (URN)10.1088/1464-4258/9/3/010 (DOI)
Available from: 2007-08-30 Created: 2007-08-30 Last updated: 2009-05-12
Tvingstedt, K., Rahachou, A., Persson, N.-K., Zozoulenko, I. V. & Inganäs, O. (2007). Surface plasmon increased absorption in polymer photovoltaic cells. Applied Physics Letters, 91(11), 113514 -
Open this publication in new window or tab >>Surface plasmon increased absorption in polymer photovoltaic cells
Show others...
2007 (English)In: Applied Physics Letters, ISSN 0003-6951, E-ISSN 1077-3118, Vol. 91, no 11, p. 113514 -Article in journal (Refereed) Published
Abstract [en]

The authors demonstrate the triggering of surface plasmons at the interface of a metal grating and a photovoltaic bulk heterojunction blend of alternating polyfluorenes and a fullerene derivative. An increased absorption originating from surface plasmon resonances is confirmed by experimental reflection studies and theoretical modeling. Plasmonic resonances are further confirmed to influence the extracted photocurrent from devices. More current is generated at the wavelength position of the plasmon resonance peak. High conductivity polymer electrodes are used to build inverted sandwich structures with top anode and bottom metal grating, facilitating for triggering and characterization of the surface plasmon effects.

National Category
Natural Sciences
Identifiers
urn:nbn:se:liu:diva-14621 (URN)10.1063/1.2782910 (DOI)
Available from: 2007-08-30 Created: 2007-08-30 Last updated: 2017-12-13Bibliographically approved
Rahachou, A. (2007). Theoretical studies of light propagation in photonic and plasmonic devices. (Doctoral dissertation). : Universitetsbibliotek
Open this publication in new window or tab >>Theoretical studies of light propagation in photonic and plasmonic devices
2007 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

Photonics nowadays is one of the most rapidly developing areas of modern physics. Photonic chips are considered to be promising candidates for a new generation of high-performance systems for informational technology, as the photonic devices provide much higher information capacity in comparison to conventional electronics. They also offer the possibility of integration with electronic components to provide increased functionality. Photonics has also found numerous applications in various fields including signal processing, computing, sensing, printing, and others.

Photonics, which traditionally covers lasing cavities, waveguides, and photonic crystals, is now expanding to new research directions such as plasmonics and nanophotonics. Plasmonic structures, namely nanoparticles, metallic and dielectric waveguides and gratings, possess unprecedented potential to guide and manipulate light at nanoscale.

This Thesis presents the results of theoretical studies of light propagation in photonic and plasmonic structures, namely lasing disk microcavities, photonic crystals, metallic gratings and nanoparticle arrays. A special emphasis has been made on development of high-performance techniques for studies of photonic devices.

The following papers are included:

In the first two papers (Paper I and Paper II) we developed a novel scattering matrix technique for calculation of resonant states in 2D disk microcavities with the imperfect surface or/and inhomogeneous refraction index. The results demonstrate that the surface imperfections represent the crucial factor determining the $Q$ factor of the cavity.

A generalization of the scattering-matrix technique to the quantum-mecha\-nical electron scattering has been made in Paper III. This has allowed us to treat a realistic potential of quantum-corrals (which can be considered as nanoscale analogues of optical cavities) and has provided a new insight and interpretation of the experimental observations.

Papers IV and V present a novel effective Green's function technique for studying light propagation in photonic crystals. Using this technique we have analyzed surface modes and proposed several novel surface-state-based devices for lasing/sensing, waveguiding and light feeding applications.

In Paper VI the propagation of light in nanorod arrays has been studied. We have demonstrated that the simple Maxwell Garnett effective-medium theory cannot properly describe the coupling and clustering effects of nanorods. We have demonstrated the possibility of using nanorod arrays as high-quality polarizers.

In Paper VII we modeled the plasmon-enhanced absorption in polymeric solar cells. In order to excite a plasmon we utilized a grated aluminum substrate. The increased absorption has been verified experimentally and good agreement with our theoretical data has been achieved.

Place, publisher, year, edition, pages
Universitetsbibliotek, 2007. p. 68
Series
Linköping Studies in Science and Technology. Dissertations, ISSN 0345-7524 ; 1115
Keywords
microcavities, photonic crystals, plasmonics, nanoparticles, scattering matrix technique, Green's function technique
National Category
Telecommunications
Identifiers
urn:nbn:se:liu:diva-9585 (URN)978-91-85831-45-6 (ISBN)
Public defence
2007-08-30, K3, Kåkenhus, Campus Norrköping, Linköpings universitet, Norrköping, 00:00 (English)
Opponent
Supervisors
Available from: 2007-08-30 Created: 2007-08-30 Last updated: 2009-05-12
Rahachou, A. (2006). Theoretical studies of microcavities and photonic crystals for lasing and waveguiding applications. (Licentiate dissertation). : Institutionen för teknik och naturvetenskap
Open this publication in new window or tab >>Theoretical studies of microcavities and photonic crystals for lasing and waveguiding applications
2006 (English)Licentiate thesis, comprehensive summary (Other academic)
Abstract [en]

This Licentiate presents the main results of theoretical study of light propagation in photonic structures, namely lasing disk microcavities and photonic crystals. In the first two papers (Paper I and Paper II) we present the developed novel scattering matrix technique dedicated to calculation of resonant states in 2D disk microcavities with the imperfect surface or/and inhomogeneous refractive index. The results demonstrate that the imperfect surface of a cavity has the strongest impact on the quality factor of lasing modes.

The generalization of the scattering-matrix technique to the quantum-mecha- nical case has been made in Paper III. That generalization has allowed us to treat a realistic potential of quantum-corrals (which can be considered as nanoscale analogues of optical cavities) and to obtain a good agreement with experimental observations.

Papers IV and V address the novel effective Green's function technique for studying propagation of light in photonic crystals. Using this technique we have analyzed characteristics of surface modes and proposed several novel surface-state-based devices for lasing/sensing, waveguiding and light feeding applications.

Place, publisher, year, edition, pages
Institutionen för teknik och naturvetenskap, 2006. p. 43
Series
Linköping Studies in Science and Technology. Thesis, ISSN 0280-7971 ; 1224
Keywords
photonic crystals, microcavities, microlasers, scattering matrix, Green's function
National Category
Telecommunications
Identifiers
urn:nbn:se:liu:diva-7482 (URN)91-85457-99-X (ISBN)
Presentation
2006-01-20, K3, Kåkenhus, Campus Norrköping, Norrköping, 13:15 (English)
Opponent
Supervisors
Note
Report code: LIU-TEK-LIC 2006:5Available from: 2006-10-03 Created: 2006-10-03 Last updated: 2009-03-09
Rahachou, A. & Zozoulenko, I. V. (2006). Waveguiding properties of surface states in photonic crystals. Journal of the optical society of America. B, Optical physics, 23(8), 1679-1683
Open this publication in new window or tab >>Waveguiding properties of surface states in photonic crystals
2006 (English)In: Journal of the optical society of America. B, Optical physics, ISSN 0740-3224, Vol. 23, no 8, p. 1679-1683Article in journal (Refereed) Published
Abstract [en]

We propose and analyze novel surface-state-based waveguides in bandgap photonic crystals. We discuss the surface-mode band structure, the field localization, and the effect of imperfections on the waveguiding properties of the surface modes. We demonstrate that surface-state-based waveguides can be used to achieve directional emission out of the waveguide. We also discuss the application of the surface-state waveguides as efficient light couplers for conventional photonic crystal waveguides.

National Category
Engineering and Technology
Identifiers
urn:nbn:se:liu:diva-14619 (URN)10.1364/JOSAB.23.001679 (DOI)
Available from: 2007-08-30 Created: 2007-08-30
Rahachou, A. & Zozoulenko, I. (2006). Waveguiding properties of surface states in photonic crystals, physics/0510273. Journal of Lightwave Technology
Open this publication in new window or tab >>Waveguiding properties of surface states in photonic crystals, physics/0510273
2006 (English)In: Journal of Lightwave Technology, ISSN 0733-8724, E-ISSN 1558-2213Article in journal (Refereed) Submitted
National Category
Natural Sciences
Identifiers
urn:nbn:se:liu:diva-14031 (URN)
Available from: 2006-10-03 Created: 2006-10-03 Last updated: 2017-12-13
Rahachou, A. & Zozoulenko, I. (2005). Light propagation in finite and infinite photonic crystals: The recursive Greens function technique. Physical Review B. Condensed Matter and Materials Physics, 72(15), 155117-
Open this publication in new window or tab >>Light propagation in finite and infinite photonic crystals: The recursive Greens function technique
2005 (English)In: Physical Review B. Condensed Matter and Materials Physics, ISSN 1098-0121, E-ISSN 1550-235X, Vol. 72, no 15, p. 155117-Article in journal (Refereed) Published
Abstract [en]

We report a computational method based on the recursive Green’s function technique for calculation of light propagation in photonic crystal structures. The advantage of this method in comparison to the conventional finite-difference time domain (FDTD) technique is that it computes Green’s function of the photonic structure recursively by adding slice by slice on the basis of Dyson’s equation. This eliminates the need for storage of the wave function in the whole structure, which obviously strongly relaxes the memory requirements and enhances the computational speed. The second advantage of this method is that it can easily account for the infinite extension of the structure both into air and into the space occupied by the photonic crystal by making use of the so-called “surface Green’s functions.” This eliminates the spurious solutions (often present in the conventional FDTD methods) related to, e.g., waves reflected from the boundaries defining the computational domain. The developed method has been applied to study scattering and propagation of the electromagnetic waves in the photonic band-gap structures including cavities and waveguides. Particular attention has been paid to surface modes residing on a termination of a semi-infinite photonic crystal. We demonstrate that coupling of the surface states with incoming radiation may result in enhanced intensity of an electromagnetic field on the surface and very high Q factor of the surface state. This effect can be employed as an operational principle for surface-mode lasers and sensors.

National Category
Engineering and Technology
Identifiers
urn:nbn:se:liu:diva-14030 (URN)10.1103/PhysRevB.72.155117 (DOI)
Available from: 2006-10-03 Created: 2006-10-03 Last updated: 2017-12-13
Zozoulenko, I. & Rahachou, A. (2005). Q factors and resonant states of whispering-gallery-mode dielectric microdisk cavities for lasing applications. Proceedings of SPIE, 5708, 210-221
Open this publication in new window or tab >>Q factors and resonant states of whispering-gallery-mode dielectric microdisk cavities for lasing applications
2005 (English)In: Proceedings of SPIE, ISSN 0361-0748, Vol. 5708, p. 210-221Article in journal (Refereed) Published
National Category
Engineering and Technology
Identifiers
urn:nbn:se:liu:diva-32375 (URN)18273 (Local ID)18273 (Archive number)18273 (OAI)
Available from: 2009-10-09 Created: 2009-10-09 Last updated: 2011-01-12
Rahachou, A. & Zozoulenko , I. V. (2004). Elastic scattering of surface electron waves in quantum corrals: Importance of the shape of the adatom potential. Physical Review. B Condensed Matter and Materials Physics, 70(23), 233409-
Open this publication in new window or tab >>Elastic scattering of surface electron waves in quantum corrals: Importance of the shape of the adatom potential
2004 (English)In: Physical Review. B Condensed Matter and Materials Physics, ISSN 1098-0211, Vol. 70, no 23, p. 233409-Article in journal (Refereed) Published
Abstract [en]

We report elastic scattering theory for surface electron waves in quantum corrals defined by adatoms on the surface of noble metals. We develop a scattering-matrix technique that allows us to account for a realistic smooth potential profile of the scattering centers. Our calculations reproduce quantitatively all the experimental observations, which is in contrast to previous theories (treating the adatoms as point scatterers) that require additional inelastic channels of scattering into the bulk in order to achieve the agreement with the experiment. Our findings thus indicate that accounting for a realistic potential as well as using the exact numerical schemes is important in achieving detailed agreement as well as interpretation of the experiment.

National Category
Engineering and Technology
Identifiers
urn:nbn:se:liu:diva-14617 (URN)10.1103/PhysRevB.70.233409 (DOI)
Available from: 2007-08-30 Created: 2007-08-30 Last updated: 2009-02-26
Rahachou, A. & Zozoulenko, I. (2004). Scattering matrix approach to the resonant states and Q values of microdisk lasing cavities. Applied Optics, 43(8), 1761-1772
Open this publication in new window or tab >>Scattering matrix approach to the resonant states and Q values of microdisk lasing cavities
2004 (English)In: Applied Optics, ISSN 0003-6935, Vol. 43, no 8, p. 1761-1772Article in journal (Refereed) Published
Abstract [en]

We develop a scattering matrix approach for the numerical calculation of resonant states and Q values of a nonideal optical disk cavity with an arbitrary shape and with an arbitrary varying refraction index. The developed method is applied to study the effect of surface roughness and inhomogeneity of the refraction index on Q values of microdisk cavities for lasing applications. We demonstrate that even small surface roughness (Δr ≲ λ/50) can lead to a drastic degradation of high-Q cavity modes by many orders of magnitude. The results of the numerical simulation are analyzed and explained in terms of wave reflection at a curved dielectric interface, combined with an examination of Poincaré surfaces of section and of Husimi distributions.

National Category
Engineering and Technology
Identifiers
urn:nbn:se:liu:diva-14616 (URN)10.1364/AO.43.001761 (DOI)
Available from: 2007-08-30 Created: 2007-08-30 Last updated: 2009-05-29
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