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  • About
  • The Global ETD Search service is a free service for researchers to find electronic theses and dissertations. This service is provided by the Networked Digital Library of Theses and Dissertations.
    Our metadata is collected from universities around the world. If you manage a university/consortium/country archive and want to be added, details can be found on the NDLTD website.
1

Broadband coherent light generation in Raman-active crystals driven by femtosecond laser fields

Zhi, Miaochan 15 May 2009 (has links)
I studied a family of closely connected topics related to the production and application of ultrashort laser pulses. I achieved broadband cascade Raman generation in crystals, producing mutually coherent frequency sidebands which can possibly be used to synthesize optical pulses as short as a fraction of a femtosecond (fs). Unlike generation using gases, there is no need for a cumbersome vacuum system when working with room temperature crystals. Our method, therefore, shows promise for a compact system. One problem for sideband generation in solids is phase matching, because the dispersion is significant. I solved this problem by using non-collinear geometry. I observed what to our knowledge is a record-large number of spectral sidebands generated in a popular Raman crystal PbWO4 covering infrared, visible, and ultraviolet spectral regions, when I applied two 50 fs laser pulses tuned close to the Raman resonance. Similar generation in diamond was also observed, which shows that the method is universal. When a third probe pulse is applied, a very interesting 2-D color array is generated in both crystals. As many as 40 anti-Stokes and 5 Stokes sidebands are generated when a pair of time-delayed linear chirped pulses are applied to the PbWO4 crystal. This shows that pulses with picosecond duration, which is on the order of the coherence decay time, is more effective for sidebands generation than Fourier transform limited fs pulses. I also studied the technique of fs coherent Raman anti-Stokes scattering (CARS) which is used as a tool for detecting dipicolinic acid, the marker molecule for bacterial spores. I observed that there is a maximum when the concentration dependence of the near-resonant CARS signal is measured. I presented a model to describe this behavior, and found an analytical solution that agrees with our experimental data. Theoretically, I explored a possible application for single-cycle pulses: laser induced nuclear fusion. I performed both classical and quantum mechanical calculations for a system of two nuclei moving under a superintense ultrashort field. From our calculation I noted that the nuclear collisions occur on a sub-attosecond time scale, and are predicted to result in an emission of zeptosecond bursts of light.
2

Emotionerna stolthet och skam och de divergerande multiplexa sociala banden : En intervjustudie av tre ungdomars sociala nätverk av sociala band och dess oscillation mellan att existera på och utanför Internet

Fürst, Henrik January 2007 (has links)
<p>The purpose of this qualitative study has been; how social bonds are interlaced between thesocial worlds contained within the analytical division of “outside Internet” and “withinInternet”. What happens with the social bond as the individual oscillate between this analyticbisection? This purpose raises important questions of the use of Internet in everyday life.</p><p>A new stance is taken toward studying the Internets integration into everyday life. The focusis adjusted to the importance of emotions. Emotions of pride and shame will be treated as thesignals of social bonds state and will indicate the resistance or openness of this integration.Goffmans theory on face-work will be used as a complement. A cognitive approach on socialbonds will assist the emotional approach. This is interwoven with a perspective forunderstanding Internet as a medium in form rather than only to focus on the “content”.</p><p>The conclusion consists of a required consistency between the quality of the social bond onthe Internet and outside the Internet. The fear of inconsistency had to do with a threat of lossof face, not to come in conflict with established norms from outside the Internet.Development of close and intimate social bonds on the Internet that didn’t have a counterpartor was in inconsistency with the social bond outside Internet, lead to shame that threatenedthe social bond. The integration of Internet in everyday life is therefore not accomplished.Still, a new generation with instant access to the Internet is to be primary socialized undernew conditions.</p>
3

Emotionerna stolthet och skam och de divergerande multiplexa sociala banden : En intervjustudie av tre ungdomars sociala nätverk av sociala band och dess oscillation mellan att existera på och utanför Internet

Fürst, Henrik January 2007 (has links)
<p>The purpose of this qualitative study has been; how social bonds are interlaced between the social worlds contained within the analytical division of “outside Internet” and “within Internet”. What happens with the social bond as the individual oscillate between this analytic bisection? This purpose raises important questions of the use of Internet in everyday life.</p><p>A new stance is taken toward studying the Internets integration into everyday life. The focus is adjusted to the importance of emotions. Emotions of pride and shame will be treated as the signals of social bonds state and will indicate the resistance or openness of this integration. Goffmans theory on face-work will be used as a complement. A cognitive approach on social bonds will assist the emotional approach. This is interwoven with a perspective for understanding Internet as a medium in form rather than only to focus on the “content”.</p><p>The conclusion consists of a required consistency between the quality of the social bond on the Internet and outside the Internet. The fear of inconsistency had to do with a threat of loss of face, not to come in conflict with established norms from outside the Internet. Development of close and intimate social bonds on the Internet that didn’t have a counterpart or was in inconsistency with the social bond outside Internet, lead to shame that threatened the social bond. The integration of Internet in everyday life is therefore not accomplished. Still, a new generation with instant access to the Internet is to be primary socialized under new conditions.</p>
4

Emotionerna stolthet och skam och de divergerande multiplexa sociala banden : En intervjustudie av tre ungdomars sociala nätverk av sociala band och dess oscillation mellan att existera på och utanför Internet

Fürst, Henrik January 2007 (has links)
The purpose of this qualitative study has been; how social bonds are interlaced between the social worlds contained within the analytical division of “outside Internet” and “within Internet”. What happens with the social bond as the individual oscillate between this analytic bisection? This purpose raises important questions of the use of Internet in everyday life. A new stance is taken toward studying the Internets integration into everyday life. The focus is adjusted to the importance of emotions. Emotions of pride and shame will be treated as the signals of social bonds state and will indicate the resistance or openness of this integration. Goffmans theory on face-work will be used as a complement. A cognitive approach on social bonds will assist the emotional approach. This is interwoven with a perspective for understanding Internet as a medium in form rather than only to focus on the “content”. The conclusion consists of a required consistency between the quality of the social bond on the Internet and outside the Internet. The fear of inconsistency had to do with a threat of loss of face, not to come in conflict with established norms from outside the Internet. Development of close and intimate social bonds on the Internet that didn’t have a counterpart or was in inconsistency with the social bond outside Internet, lead to shame that threatened the social bond. The integration of Internet in everyday life is therefore not accomplished. Still, a new generation with instant access to the Internet is to be primary socialized under new conditions.
5

Emotionerna stolthet och skam och de divergerande multiplexa sociala banden : En intervjustudie av tre ungdomars sociala nätverk av sociala band och dess oscillation mellan att existera på och utanför Internet

Fürst, Henrik January 2007 (has links)
The purpose of this qualitative study has been; how social bonds are interlaced between thesocial worlds contained within the analytical division of “outside Internet” and “withinInternet”. What happens with the social bond as the individual oscillate between this analyticbisection? This purpose raises important questions of the use of Internet in everyday life. A new stance is taken toward studying the Internets integration into everyday life. The focusis adjusted to the importance of emotions. Emotions of pride and shame will be treated as thesignals of social bonds state and will indicate the resistance or openness of this integration.Goffmans theory on face-work will be used as a complement. A cognitive approach on socialbonds will assist the emotional approach. This is interwoven with a perspective forunderstanding Internet as a medium in form rather than only to focus on the “content”. The conclusion consists of a required consistency between the quality of the social bond onthe Internet and outside the Internet. The fear of inconsistency had to do with a threat of lossof face, not to come in conflict with established norms from outside the Internet.Development of close and intimate social bonds on the Internet that didn’t have a counterpartor was in inconsistency with the social bond outside Internet, lead to shame that threatenedthe social bond. The integration of Internet in everyday life is therefore not accomplished.Still, a new generation with instant access to the Internet is to be primary socialized undernew conditions.

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