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Modelling of Pulse Propagation in Nonlinear Photonic Structures
Sterkhova, Anna ; Richter, Ivan (oponent) ; Samek, Ota (oponent) ; Petráček, Jiří (vedoucí práce)
The demand for more effective data-storage and faster signal processing is growing with every day. That is why the attention of the scientists is focused on the all-optical devices, which can improve the above mentioned requirements. Microring optical resonators are among the state of art devices, that are under consideration. There is a variety of numerical techniques to simulate processes occurring while the optical signal propagates in the microring resonator structure. They differ in its calculation effectivity, used approximations and possibilities of application. The aim of this work was to develop two simple and practical numerical methods for simulation of pulse propagation in nonlinear waveguide structures. It was also demanded, that opposed to the commonly known and frequently used finite-difference time-domain (FD-TD) method, the newly developed techniques could be easily applicable for the study of nonlinear structures based on microring resonators. That is why developed methods use some approximations, namely the slowly varying envelope approximation. The methods advantage is high speed and low requirements of computational resources. Both techniques are based on observation that waveguide structures that use microring optical resonators can be considered as composed of single waveguides and waveguide couplers. The first numerical technique solves coupled partial differential equations, which describe pulse envelope propagation in the structure. This method uses the “up-wind” scheme, which is suitable for the partial differential equations that describe the wave propagation. The second developed technique is derived from the first one. The difference between methods is in the treatment of the coupling between two waveguides. If in the first method the coupling is considered as the real one, distributed on the given length, in the second method the coupling is considered to be concentrated in one point. Due to this approximation it is possible to integrate the appropriate equations and achieve significant increase of calculation speed. Quasianalytical character of the second method enables also easy identification of different types of steady-state solutions. Due to these properties the second method was used to study spontaneous generation of optical pulses in the structures, consisting of coupled ring resonators. Both methods, which were developed during this work, represent fast and physically illustrative alternatives to the FD-TD, so it can be expected that these methods can play an important role during the research of nonlinear waveguide structures.
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Diagnostika impulzů Ti:Sa laseru pro generaci plazmatu
Weiss, Jiří ; Samek, Ota (oponent) ; Kaiser, Jozef (vedoucí práce)
Diplomová práce se zabývá studiem časových charakteristik impulzů generovaných oscilátorem s Ti:safírovým aktivním prostředím. Z hlediska vlastností laserem indukovaného plazmatu je velký důraz kladen na kvalitu svazku, především na kontrast impulzů. Byl navržen nový prototyp autokorelátoru třetího řádu, zařízení pro měření laserového kontrastu metodou kombinování původního laserového impulzu s jeho kopií jiné vlnové délky. Dynamický rozsah popisovaného autokorelátoru má podle předpokladu dosahovat až 8×10^12, což je více než mají současná komerčně dostupná zařízení.
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Modification of the focusing part of the table-top setup for Laser Induced Breakdown Spectroscopy (LIBS)
Borovský, Ján ; Prochazka, David (oponent) ; Samek, Ota (vedoucí práce)
This bacheolor thesis solves functional modifications of the foccusing part of the table-top setup for laser induced breakdown spectroscopy LIBS. Main requirements for modified draft includes increasing view field of the navigation camera, increasing the setup’s aperture and prevention of the camera destruction by radiation of plasma. These requirements were fulfilled in new draft of optical stand including possible solution as enlarging focusing lens, new dielectric mirror and mechanical iris shutter. Some elements of proposed solution will be used in suggestion of Tescan company‘s new interaction chambers for LIBS analysis.
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Ramanovská pinzeta: princip a aplikace
Bernatová, Silvie ; Samek, Ota ; Pilát, Zdeněk ; Ježek, Jan ; Kaňka, Jan ; Šiler, Martin ; Zemánek, Pavel
Ramanovská pinzeta kombinuje optickou pinzetu a ramanovskou mikrospektroskopii. Silové účinky fokusovaného laserového svazku zacíleného na mikrometrové objekty (živé i neživé) umožní prostorové zachycení objektů (tzv. optická pinzeta).Záření nepružně rozptýlené zachyceným objektem (Ramanův rozptyl) nese informaci o molekulárních vazebných vibracích v objektu a napomáhá určit jeho chemické složení s mikrometrovým prostorovým rozlišením (tzv. ramanovská mikrospektroskopie). Jediný laserový svazek nám tak umožní bezkontaktně a sterilně zachytit mikroobjekty v kapalině a současně je diagnostikovat, aniž by byla poškozena jejich struktura nebo fyziologie. Vlnová délka je volena tak, aby nedocházelo k absorpci záření a tím i k destrukci objektu a současně, aby byl Ramanův rozptyl detekovatelný. Pro živé mikroorganismy je vhodné volit delší vlnové délky (700-900 nm). Při takto zvolené vlnové délce, je možné požadovaný objekt sledovat i několik hodin (tzv. časosběrná měření) nebo naopak sledovat velmi rychlé dynamické procesy.
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Classical and advanced methods of optical micromanipulations and their applications
Zemánek, Pavel ; Brzobohatý, Oto ; Šiler, Martin ; Karásek, Vítězslav ; Samek, Ota ; Jákl, Petr ; Šerý, Mojmír ; Ježek, Jan
Optical micro-manipulation techniques have been using for more than 30 years to transfer the momentum from light to microparticles or nanoparticles and influence their movement in liquid, on the surface, or in the air. These days such techniques become more developed and frequently used in physics, chemistry and biology to manipulate, trap, rotate, or sort various types of objects, including living cells in a contactless and gentle way.
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