简介:AnewlygrownBaGa4Se7crystalhasbeensynthesizedviatheBridgman-Stockbargertechnique.Thisnewcrystalhasadvantagesofhighnonlinearoptics(NLO)coefficients,highlaserdamagethresholds,andwidetransparentregions.TheBaGa4Se7crystalhasbrightapplicationprospectsasanonlineargainmediuminmid-infraredandterahertzregions.Inthispaper,thecrystallinestructureandsyntheticmethodoftheBaGa4Se7crystalareintroduced.Therefractiveindicesandabsorptioncoefficientsalongthreedielectricaxesbetween0.1THzand1.0THzarealsoobtained.Theterahertzdifferencefrequencygeneration(THz-DFG)characteristicsbasedontheBaGa4Se7crystalinthefrequencyrangeof0.1THzto1.0THzareanalyzedtheoreticallyandthephase-matchingconditionsarecalculated.TheapplicationofBaGa4Se7crystalsinterahertzwavegenerationisalsodiscussed.
简介:Side-matchvectorquantization(SMVQ)achievesbettercompressionperformancethanvectorquantization(VQ)inimagecodingduetoitsexplorationofthedependenceofadjacentpixels.However,SMVQhasthedisadvantageofrequiringexcessivetimeduringtheprocessofcoding.Therefore,thispaperproposesafastimagecodingalgorithmusingindirect-indexcodebookbasedonSMVQ(IIC-SMVQ)toreducethecodingtime.Twocodebooks,namedindirect-indexcodebook(II-codebook)andentire-statecodebook(ES-codebook),aretrainedandutilized.TheII-codebookistrainedbyusingtheLinde-Buzo-Gray(LBG)algorithmfromside-matchinformation,whiletheES-codebookisgeneratedfromtheclusteredresidualblocksonthebasisoftheII-codebook.Accordingtotherelationshipbetweenthesetwocodebooks,thecodewordintheII-codebookcanberegardedasanindicatortoconstructafastsearchpath,whichguidesinquicklydeterminingthestatecodebookfromtheES-codebooktoencodetheto-be-encodedblock.TheexperimentalresultsconfirmthatthecodingtimeoftheproposedschemeisshorterthanthatofthepreviousSMVQ.
简介:Thenear-ultraviolet(n-UV)excitedblue-emittingSr2MgSi2O7:Eu2+phosphorsareusedforfluorescencelampandtricolorwhiteLEDs.Theeffectofnitrogen-dopedonthestructureofthehostandtheenhancementofphotoluminescenceisexperimentallyinvestigated.Theresultsshowthatastheamountofnitrogen-dopedvariesfrom0to0.6(at.),theluminousintensityisfoundtobeincreasedto169%,andthepartialreplacementofObyNresultsinachangeofthecrystalfieldbymodifyingthesymmetryofthecrystalstructure.Asaresult,withthenitrogen-dopedinsmallamount,theluminousintensity,chromaticitycoordinatesandthecolorpuritycanbeadjustedtoadesiredvalueintheapplications.