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Theoretical Study On The Emission Characteristics Of Random Lasers

Posted on:2007-04-26Degree:DoctorType:Dissertation
Country:ChinaCandidate:C WangFull Text:PDF
GTID:1118360242462071Subject:Physical Electronics
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Scattering is regarded as detrimental factor in conventional lasers. But it is multiple scattering that makes random lasing possible. Random laser theory is about how lightwave propagates in random gaining media. Random laser theory is complicated, which concern localization theory and laser physics. Random lasing is intensively investigated for its wide prospective.In this dissertation we investigate several theoretical problems of random lasing system as follows.(1) We study the dependence of modes on polarization in random gaining media. In conventional lasers the frequency of modes do not denpend on polarization stages. In random lasers what is the relation between them? For scattering particles with same spacial distribute, the properties of random system with varied polarization are computed numerically. It is denoted that the quality factor, emission frequency and spacial pattern of modes are dependent on polarization heavily.(2) Emission characteristics of one-dimensional and two-dimensional anisotropic random laser are investigated. So far all the random lasers are based on spacially disordered and isotropic material. We present a new conceptional random laser based on spacially orderly and anisotropic material. For anisotropic random laser, when scattering particles are spatially orderly, the disorder of optic axis can make the media to be diffusive regime or localized regime. When the extent of disorder of optic axis increase, the state transition from diffusive regime to localized regime occurs. Thus a new mechanism for random lasing is presented.(3) We study the temporal evolvement property of quasi-mode spatial distribute and frequency property of quasi-mode in one-dimensional random laser. The formation time of localized state depend on pumping intensity. Stronger the pumping intensity is, shorter the formation time of localized state. So in experiments the width of pulse and energy of pulse must be provided properly. The narrow pulse with great energy can make the localized state form in one pumping pulse. We investigate how dielectric layers of different position influence the frequency of mode. The dimension modifying of dielectric layers in localized center change the emission frequency of mode. But the dimension modifying of dielectric layers beyond localized position donot change it.(4) We study the characteristics of saturation and threshold of two-dimensional random laser. By numerical computing, we find that the characteristics of threshold and saturation are revealed clearly when the pumping intensity varies in two-dimensional random laser. It denotes that coherent feedback really occur in two-dimensional random gain media. Better the localization extent of modes are, less the thresholds are. But the localization extent of mode is not the only factor that influences the threshold. The mode whose lifetime is longer has less threshold.(5) The morphology and temporal dependence of the power spectra in two-dimensional random media are studied. Emission spectra are dependent on morphology factor in two-dimensional random laser. The power spectra are different in varied morphology and same random formation.(6) The time evolution of power spectrum of quasi-modes in two-dimensional random medium is investigated. By numerical computing, the process of generation and selection of modes in random media are obtained.
Keywords/Search Tags:Anderson localization, Finite difference time-domain method, Random lasing, Emission Characteristics
PDF Full Text Request
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