1,007 research outputs found
The author and the text: linguistic analysis of andrius tapinas' commentaries.
No full textThe author and the text: linguistic analysis of Andrius Tapinas' commentaries This bachelor thesis analyses the commentaries of Andrius Tapinas and the aim is to identify authors position. The problem of authors position explorations is that it is frequent to decide about authors position from interpersonal metafunction. As there are three metafunctions, which function together – ideational, interpersonal and textual – it is possible to decide about authors position from ideational and textual metafunctions as well. Analysis has shown that genre, themes and informtion structure, which belong to ideational metafunction, reveal authors didactic and civic position, use of irony shows authors will to criticize and change current situation and inform the readers. Analysis of intertextuality has shown, that author is creative and witty, elements of other texts help author to express his opinion and inform addressees. Interpersonal function revealed, that author uses first and second person forms, which help to affiliate with addressees
Translation of cultural references in the novel “hour of the wolf” by author-translator andrius tapinas.
No full textThe phenomenon of self-translation is not yet commonly seen in the translation discipline. This thesis examines Andrius Tapinas's fictional novel Vilko Valanda, which the author himself describes as "Vilnius but different". The novel is set in our real world, but it also contains fantasy (steampunk) elements that were not included in the analysis, as this study focused on real culture-specific items, with the exception of proper nouns. This study analyses how author-translator Andrius Tapinas translated his work Hour of the Wolf into English, what translation strategies he used to translate culture-specific items, and whether he took a more detached translator's stance, or took advantage of his own stance as an author to make changes in the translation that translators would avoid. The study used Jurgita Mikutytė's (2005) and Shih Chung-ling's (2010) classifications of culture-specific items and Eirlys Davies' (2003) classification of translation strategies in order to answer the questions posed. A total of 319 culture-specific items were found in the original novel and 312 in the translation, as in some cases it was chosen to omit culture-specific items in the translation. The author-translator concept, the classification of culture-specific items and translation strategies are discussed in this paper. The data found is presented both quantitatively and qualitatively, giving a percentage breakdown of all the culture-specific item groups and the percentage frequency of translation strategies used. Translation within each subgroup of cultural realities is then discussed with examples. Finally, conclusions are presented, answering the questions raised and summarizing the whole study. The results of the study showed that the largest group of cultural realities was proper nouns, and the second largest group was slang and idioms. It was also found that the author-translator most frequently used localization translation strategy, with transformation in second place. A more detailed analysis showed that author-translator Andrius Tapinas followed the translator's stance and did not make any significant changes in the translation and tried to bring new readers closer to the novel by using the translation strategies of localization, transformation and addition. This study may be of interest to translators and writers who are interested in the author-translator phenomenon in the Lithuanian translation community. And a limitation of this study is that for some of the culture-specific item groups examples were not found in the novel, so it may have been better to concentrate on fewer groups and to analyse them in more depth instead
Investigation of attosecond ionization dynamics in gases and solids with intense few-cycle laser pulses
No full textInteraction of intense light fields with dielectric materials has fascinated scientists since the invention of pulsed lasers in the early sixties. Despite the many decades of research, the interest in the field keeps growing because of the potential technological applications of optical (meta-) materials and the prospects of light-controlled peta-Hertz electronics as well as the improving understanding of the fundamental processes behind light-matter interactions. The progress in the short-pulse laser technology that delivered ever-shorter light pulses was echoed by the discoveries of different progressively shorter time scales in the cycle of excitation and energy/charge relaxation in transparent solids, many parts of which are now well understood. The ultimate challenge lies in recovering the earliest stages of the dynamics which are linked to optical-field-ionization that proceeds within a fraction of an optical cycle. One of the complications of advancing the attosecond science to the bulk media is the problem of inducing and detecting a synchronized attosecond response. The charged particles spectroscopy, well developed in gaseous media during last decade and capable of reaching an attosecond temporal resolution cannot be used as an experimental tool for investigation since direct detection of charged particles is impossible in the volume of a solid material.However, solids are the natural place where electronic processes on the sub-femtosecond or attosecond time scale are expected. Very recently several methods for measuring attosecond dynamics in condensed media have been proposed utilizing optical fields in the transparency range of the material.In this thesis a method, suggested in our scientific group is presented.It is an all-optical method based on the detection of optical harmonics originating from ultrafast modulation of a free electron current due to ionization in the field of intense few-cycle laser pulses. This technique will allow retrieving the temporal dynamics of ionization in transparent solids. It can also be considered as an all-optical alternative to the methods of attosecond metrology based on the detection of charged particles. The experiments on the optical-field-ionization in solids are discussed along with the description of the main technologies used in generation and characterization of few-cycle near-IR laser pulses. Characterization of ultra-broadband ultra-short pulses is a separate important problem. A new bandwidth unlimited pulse measurement technique based on quasi-linear temporal phase modulation in a gas weakly ionized by a long pump pulse is presented in this thesis.The most direct way to investigate the electron dynamics in different systems with a high temporal resolution is to employ time-resolved spectroscopy where the initiating and probing optical events are substantially shorter then the characteristic time of the process under investigation. The substantial progress in the development of XUV technologies and attosecond science in the recent years resulted in a remarkable success in studying ionization dynamics in atoms and molecules with a sub-femtosecond time resolution. The closing part of this thesis is dedicated to the time- and energy-resolved measurements of Auger decay in Krypton and Xenon using attosecond XUV-pump-IR-probe spectroscopic technique.<br /
New approaches to driving mid-IR parametric frequency converters
No full textMany scientific and industrial applications demand high energy ultrashort mid-IR pulses. However, this spectral region is difficult to access directly with lasers because of the lack of broadband laser materials suitable for developing ultrashort pulse lasers and amplifiers in the mid-IR. As it was demonstrated during recent years, an alternative approach to generate intense pulses in the mid-IR is optical parametric (chirped pulse) amplification. Parametric down-conversion is restricted by the transmission windows of the nonlinear optical crystals and phase-matching. This makes a unique combination of characteristics of pump lasers and properties of NLO crystals important for efficient amplification of mid-IR pulses. For example, zinc germanium phosphide (ZGP) nonlinear crystals have high nonlinearity and broad amplification bandwidth, however they are transparent only from 2 μm, which makes conventional Ytterbium, Neodymium or Titanium based lasers not suitable for direct pumping of ZGP OPAs. In this thesis we explore new approaches for driving mid-IR frequency converters based on ZGP NLO crystals. Those involve a development of novel Ho:YAG laser system operating at 2.09 μm wavelength and implementation of cascaded parametric down conversion relying on a combination of Ytterbium and Holmium pump lasers. For scaling up the pump pulse energy we designed an ytterbium laser amplifier operating in the pulse burst amplification mode. We demonstrate a coherent pulse stacking technique, by which amplified pulse burst can be stacked into to a single high energy pulse. As an alternative to coherent pulse stacking we introduce a concept of a hybrid optical parametric chirped pulse amplifier pumped by a burst of picosecond pulses originating from a joule-class Nd:YAG laser. The laser systems, developed in this work, are not only valuable as pump sources for longwave frequency down-conversion, but are also relevant as stand-alone lasers for technological applications. To highlight this point, we examine an applicability of the developed Ho:YAG laser for material processing. We demonstrate, that 2.09-μm laser pulses with of a few picosecond duration and microjoule energy are optimal for de-bonding of metals through silicon substrates
Optical and mode-locking properties of InGaN/GaN based hetero-structures
No full textShort wavelength pulsed lasers are indispensable for high density and high speed optical data acquisition, storage and transfer applications. Passively mode-locked blue lasers are an attractive alternative for blue laser sources achieved by non-linear frequency conversion techniques. Although over the recent years it has been shown that InGaN/GaN based hetero-structures can be used as potential material for the fabrication of saturable absorbers, passive mode-locking in the blue spectral range has not been realized yet. The main reason for that is the complicated microscopic nature of InGaN/GaN materials and the difficulty to control the dynamics of photo-induced carriers which determine mode-locking properties of the material. In this work, we have characterized different InGaN based hetero-structures as potential saturable absorbers. Three different groups of the samples have been investigated: i) quantum well samples with different numbers of quantum wells grown under optimal conditions; ii)quantum well samples with modified optical properties due to different buffer layer thickness and postgrowth treatment; iii) a multilayered quantum dot sample.The characterized quantum well samples exhibit relatively high optical quality and sufficiently high saturable losses (which can be controlled by alternating a number of the quantum wells). Nevertheless, they have two major disadvantages as saturable absorbers, namely, a very long absorption recovery time (in the order of a few nanoseconds) and a rather high saturation fluence. The long recovery times are not desirable for achieving a stable and self-starting mode-locking without Q-switching.In order to understand the relaxation processes of photo-induced carriers that determine the absorption recovery times of the saturable absorbers, optical properties of the hetero-structures have been extensively studied by using the frequency and time resolved photo-luminescence technique. The obtained data reveal that, directly after excitation into free states, the photo-induced carriers relax very fast to the localized states with different localization energies. The main processes that cause further relaxation are energy transfer between the different localized states, relaxation to lower lying defect states, and recombination. The density of defects and dislocations was found to play a crucial role in the relaxation dynamics. Since in the case of multiple quantum well samples grown under optimal conditions, number of defects and dislocations is rather limited, the relaxation is dominated by recombination from the localized excitonic states which causes rather long absorption recovery times.By using different spectroscopic techniques, we have investigated the modified QW samples, designed to speed up the relaxation of photo-induced carriers. These multiple quantum well samples have been modified by introducing additional defects in two different ways: i) the samples were grown with substantially thinner buffer layers; ii) the samples grown under optimal conditions were bombarded by an ion beam. In the case of first modification, substantially shorter absorption recovery times (in the order of a few tens of picoseconds) have been measured and the saturation fluence was found to be slightly decreased. However, the optical quality of the samples has degraded severely, which makes the heterostructures unsuitable for mode-locking applications. In the case of multiple quantum well hetero-structure grown under optimal conditions and after treated by the ion bombardment, the absorption recovery times have been slightly reduced while an optical quality of the sample remained unchanged. This reveals that the modification of optical properties of InGaN based hetero-structures by ion bombardment is a promising approach to improve the performance of such absorbers.Quantum dot-based hetero-structure was identified to be significantly superior to the QW hetero-structures discussed above, in terms of mode-locking properties. It exhibits rather a good optical quality, high saturable losses, substantially lower saturation fluence and rather fast absorption recovery time. Frequency resolved pump probe measurements revealed that the quantum dot hetero-structure can be used in a relatively broad spectral range. Furthermore, by studying the dynamics of photo-induced carriers in the quantum dot hetero-structure a very interesting phenomenon has been observed. Namely, the dynamics of the photo-induced carriers in the quantum dot heterostructure have been found to be very strongly influenced by excitation energy, wavelength and repetition rate which was attributed to the effect of local heating.This, to our knowledge, is one of the first such extensive studies of the dependence of optical properties of the InGaN quantum dot hetero-structures on excitation conditions.<br /
Sub-cycle control of light waves
Get PDFAttosecond physics is becoming an established methodology for directly probing the fastest processes in nature. Attosecond optics is enabled by strong field phenomena and relies on ionization and control of electron wave-packets in a very rapidly oscillating optical field. Consequently, strong field ionization is the starting point of all typically studied strong field phenomena, such as above threshold ionization (ATI), coherent and incoherent Xray generation and THz emission from laser plasmas. When a strong periodic driving field suppresses the binding potential of an electron in an atom, molecule or crystal, the electron can tunnel out to become a quasi-free particle within a tiny fraction of the driving optical cycle of the laser pulse twice per optical cycle near the peak of each prominent half cycle. This thesis describes novel tools and methods for controlling the ionization via shaping of the light waveforms on a sub-cycle level. For the measurement of the ionization dynamics optical methods are developed that rely on the detection of secondary radiation emitted in the THz and XUV spectral ranges. As suggested by Brunel two decades ago, the sharp bursts of electrons ejected into the continuum at the peaks of optical half cycles correspond to many orders of optical harmonics of the driver frequency. For a symmetric optical cycle, the ionization bursts of equal strength occur twice per optical cycle leading to the emission of odd-numbered harmonics spaced at twice the driver frequency. By adding a field that is twice or half the frequency of the fundamental field it is possible to break the symmetry of the positive and negative field crests enabling the emission of even harmonics. A particularly interesting is the lowest-frequency emission peak that can be interpreted as a -zeroth- order harmonic sideband corresponding to the THz wave emission. In this thesis a novel scheme is described where incommensurate frequency two-color field can generate temporally modulated electric micro-currents in plasma which allow tuning of the central frequency of the THz sideband. The Brunel model was initially proposed to explain the high-order harmonic generation (HHG) in the XUV spectral range. However, the key process behind the emission of these very high order harmonics, well above the ii ionization potential of an atom, is the recollision with the parent ion. In the so-called simple man's model, the electron ejected into the continuum is accelerated by the laser field and upon its return to the parent ion a high energy photon is emitted. Optimization of HHG is a very active field of research, as it is a promising table-top source of coherent XUV and soft X-Ray radiation packed in extremely short pulses. However the main issue is low generation efficiency. The extremely short time window of this process that takes place within a fraction of half-cycle of the optical field, makes it difficult to control and tailor HHG process. We describe a method for the generation of intense waveforms that allows controlling the electric field on the attosecond time scale and it is based on Fourier synthesis of the light wave composed from several infrared color pulses. These cycle-sculpted waveforms are used for controlling the ionization bursts and subsequent trajectory of the electrons that are emitted in the continuum in a way that they are most efficiently accelerated and return to the ion therefore improving the efficiency of HHG and extending the cut-off toward higher photon energies. These multi-color waveform shaped pulses allow high degree of control over the HHG process, but it is repetitive and the attosecond pulse emission occurs many times per laser pulse. In order to limit the attosecond XUV bursts to just one per laser pulse and still be able to control the field of the pulse, a single cycle ultrashort pulses are necessary for driving HHG. We describe a novel pulse self-compression scheme that allows 20-fold shortening of pulses in the IR spectral range down to sub-cycle duration. The scheme is based on a Kagome lattice hollow core photonic crystal fiber. Upon nonlinear propagation of the pulse in the fibre due to anomalous dispersion of the waveguide that compensates the positive chirp induced by the self phase modulation, the pulse shortens by itself in a very compact setup and allows high degree of integration into a HHG setup. The main results presented in this thesis can be summarized as follows: A concept of multicolor driver pulse synthesis based on spatial and temporal superposition of waves from an optical parametric amplifier is proposed and demonstrated. Both the absolute (CEP) and relative phase of the constituent pulses at every carrier frequency is controlled. To this end, both an active phase-locking of the femtosecond pump laser and the passive phase lock resulting from the operation of a white-light-seeded OPA are employed. Continuous tunability of THz emission from a two-color-driven laser plasma is theoretically predicted and experimentally verified by means of a CEPlocked parametric generator of two incommensurate optical driver frequencies. A unified view on the generation of low-order sideband (THz emission) and higher-order optical sidebands (low-order harmonics emission) from a iii laser-driven plasma is developed based on a fully quantum-mechanical description of continuum-continuum transitions for ionized electrons as an extension of the earlier semi-classical Brunel model. Active CEP stabilization is realized for the first time on a multi-millijoule femtosecond Yb-doped amplifier. A new forward CEP stabilization technique is proposed and demonstrated on a multi-kHz repetition-rate Yb-doped amplifier. A possibility to optimize the HHG average spectral brightness and extend the spectral cut-off by means of engineering the electron trajectory in a multicolor-shaped optical cycle of a linearly-polarized driver pulse has been demonstrated experimentally and confirmed theoretically. Substantial increase of the peak intensity of the corresponding attosecond XUV bursts in the time domain is predicted. An efficiency and bandwidth improving concept for femtosecond OPA driving with shaped femtosecond Yb-pulses is proposed and demonstrated. Based on the phase-only pulse shaping, the technique yields a chirped top-hat pulse for OPA pumping while enabling, simultaneously, a fully compressed pulse required for efficient generation of the white-light seed for the OPA. Generation of externally and self-compressed pulses from a novel type of a gas-filled hollow waveguide - a Kagome-lattice photonic-crystal fiber - was explored as a means of increasing the pulse intensity and reducing the number of optical cycles of the driver laser. A sub-single-cycle transient was generated at the wavelength of 1.7 -m, which enabled XUV emission in a single isolated attosecond burst regime as evidenced by the observation of a continuous XUV spectrum free of harmonic modulation
Erzeugung von intensiven Laserpulsen im mittleren infraroten Spektralbereich und dessen Anwendung für die entfernte Abtastung von Gasen.
No full textThe dissertation is devoted to the development of a ZGP-based optical parametric amplification system for the generation of high-energy ultrashort mid-IR pulses for non-linear optical spectroscopy and remote atmospheric sensing. For pumping of the parametric amplifier a 2--m Ho:YAG chirped pulse amplifier was developed. The dissertation is concluded by research on detection of molecular gases with coherent light from an atmospheric laser, which is driven by intense mid-IR pulses
Filamentation and self-compression of multi-mJ fs mid-infrared pulses
No full textThe physics of strong-field applications, such as filamentation, laser-driven particle acceleration, generation of high harmonics and laser-plasma THz radiation, requires driver laser pulses that are both energetic and extremely short. Moreover, since these applications benefit from extending the oscillation period of the driving electromagnetic field, a longer carrier wavelength is often desirable. Due to the absence of broadband laser gain materials, the common approach for the generation of multi-mJ femtosecond mid-infrared pulses is optical parametric amplification (OPA), and it variation, optical parametric chirped pulse amplification (OPCPA). However, the peak power of the pulses from OPA and OPCPA systems is limited by the maximum energy of pump lasers and restricted by phase-matching bandwidth, as well as the nonlinear phase accumulation in crystals during parametric amplification. Therefore, an external pulse compression, leading to a corresponding peak power increase, is required. This thesis explores the methods of generation and characterization of sub-TW multi-mJ fs mid-IR pulses and investigates their propagation in the filamentation regime. We validate, that high peak-power few-cycle pulses can be generated through a nonlinear soliton-like self-compression in mm-long transparent dielectrics and in ambient air. Furthermore, we show how spectral, temporal, spatial and energetic characteristics of the mid-IR pulse, as well as plasma density and length of the filaments depend on multiple parameters, such as environmental conditions, focusing strength as well as temporal chirp, polarization and energy of the pulses
Generation and applications of high-brightness coherent soft-Xray pulses
No full textAdvances in X-ray science and technology have resulted in breakthrough discoveries ranging from unraveling the structure of DNA and proteins to visualizing atoms, molecules, and materials at the nanoscale level. One very exciting advance in X-ray science has been the ability to generate ultrafast (0.1–10 fs), coherent X-rays from a table-top apparatus, by using the extreme nonlinear optical process of high-order harmonic generation (HHG). The femtosecond-to-attosecond pulse duration and intrinsic jitter free have made it possible to capture the coupled motions of electrons, atoms, and molecules in real time. Broadband HHG sources enable novel elemental specificity absorption spectroscopy for probing transient dynamic of multiple elements simultaneously in complex chemical and biological samples. Moreover, the low divergence and capability to produce light with full spatial coherence have enabled advanced time-resolved imaging of high-performance materials and novel devices with nanometer resolutions. This thesis lays out an attractive route toward high-flux table-top HHG sources by use of broadband power-scalable Yb:CaF2 driver laser. This development targets the soft X-ray spectral range 100-240 eV with the wavelength in the 5-13 nm range where our system delivers an orders-of-magnitude improvement in the HHG flux compared to conventionally used Ti:sapphires driver lasers. The spectral range of our interest covers important absorption edges of many atoms: Si, Ga, Se (relevant for semiconductors); Tb, Gd N-edge (relevant for magnetic materials); P, S, C (relevant to organic molecules). Combining together with advantages of power scaling, cost-efficient, robust, compactness of Yb laser, the high brightness soft-X-ray source opens up novel oppor- tunities in many applications such as advanced EUV metrology, near edge absorption microscopy, ultrafast magnetic microscopy on a table-top scale. Two novel HHG approaches for HHG driving are developed in this thesis. First, we demonstrated HHG driven directly by an intense (0.7 TW peak-power), 20 fs, 2 kHz, Yb laser amplifier system for the first time in the fully absorption-saturated regime, which results in an improvement of orders of magnitude in the conversion efficiency and with highest flux 10^9 photons/s/1% bandwidth in the soft X-ray photon regime (150 eV -220 eV). This improvement can be explained by our single-atom and macroscopic simulation of the HHG process. The second driving approach generates intense isolated attosecond pulses with a multi-color driving waveform in the mid-IR wavelength range. A proof of concept waveform synthesizer is first demonstrated and multi-color temporal gating effect is discussed. Then, we present our development of a high peak- and average-power mid-IR OPA that serves as a blueprint for Fourier synthesis driver pulse for HHG, with which soft X-ray super-continua is generated corresponding to an isolated attosecond pulse with a flux of 107 photons per second reaching into the water window (> 300 eV) spectral region. To further extend HHG cut-off, we demonstrated post compression of the mid-IR pulses with multi-TW peak-power at the wavelength of 3900-nm which were characterized with a spatial-temporal pulse characterization technique in the single optical cycle regime. Many high-performance materials and novel devices consist of multiple components and possess a natural or intentional nanostructure that defines their optimal properties and performance. Exploiting the the intrinsic electron spin dynamics and its associated magnetic moment, the opto-magnetic control on a femtosecond timescale has become an important topic for fundamental research as well as technological application such as the sensor technology and in magnetic data storage devices. We implement the first table-top ultrafast resonant X-ray magnetic diffraction measurement at the N-edge of the rare-earth ferromagnets Tb (155 eV). A serials of snapshot imaging of the nanoscale magnetic structures using femtosecond X-ray pulses with sub-100 fs temporal and sub- 100 nm spatial resolution has also been recorded. To date, similar measurements have only been accomplished in large-scale X-ray facilities. The unique advantages of the soft X-ray microscopy for studying magnetic micro- and nano-structures are the element specificity of the X-ray magnetic circular dichroism (XMCD) contrast mechanism and its direct correlation with local spin and orbital moments. Improving the performance of the HHG sources will greatly benefit the advancement of ultrafast X-ray methodology and extend the range of applications and capabilities. The development of high energy booster and efficient nonlinear conversion approaches provide us a novel ultrafast light-matter experimental platform, using a wide range of the electromagnetic radiation spectrum which extends from the low frequencies of the THz pulses, covers the mid-IR and reaches up to the high energy of the soft x-ray pulses generated via HHG
The effect of task and personal relevance on credibility judgements while searching on the Internet
No full textPeople can view the Internet as an endless source of information although it is not known how individuals might evaluate the credibility of information that is presented on websites. A methodology is needed to incorporate how the information seeking task, as well as the level of personal relevance, influences the criteria individuals use to evaluate Internet information. Forty subjects completed four search tasks with two of the tasks in topic areas where subjects had a high level of interest and the other two tasks in areas where subjects had a low level of interest. For each of the topic areas the subjects were asked to complete one fact finding task and one task that required more in-depth analysis. The results revealed that there are four factors explaining the subjects’ credibility judgments: competence, coverage, presentation, and trustworthiness. Results of logistic regression suggest that the complexity of the task influences the factors used in judging the credibility of information being presented. However there appears to be no relationship between the levels of personal relevance and criteria used to judge credibility. A revised model is proposed that incorporates the four factors and illustrates how they are used in evaluating credibility.Ph.D.Includes bibliographical referencesIncludes vitaby Andrius Viktoras Kirkyl
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