Optical filter withelectromagnetically induced transparency
J. Odeurs
Abstract
Multi-level atomic coherence induced bycoupling andprobe fields canproduce manyinteresting effects suchas electromagnetically induced transparency (EIT), lasing without inversion, electromagnetically induced absorption, slow light, stopped light, nonlinear conversion withsubstantially reduced phase matching conditions, etc. EITisobserved asanarrow holeinabroadabsorption line.Steep dispersion within theEITwindowresults ina substantial reduction ofthegroupvelocity oftheprobe pulse. Onecanexpect that theabsorption andthegroupvelocity ofthepulse aresubstantially reduced ifthecarrier frequency andthespectrum oftheinput pulse areconfined inside the EITwindow.Inthis report we showthat theEITwindowcanbeusedasatime-to-frequency filter fortheprobe pulse whosespectrum ismuchbroader thanthewidth oftheEITwindow. Wedemonstrate that thenarrowspectral part ofthe pulse, coincident withtheEITwindow, develops inalong Gaussian pulse withslowgroupvelocity. Thatpartofthe pulse spectrum, whichcoincides withthemaximumoftheabsorption line, isstrongly absorbed. Sidebands ofthepulse interacting withthewings oftheabsorption line develop ina0-tpulse. Thelatter hasanoscillatory shape andthetime integral ofitsenvelope (pulse area) isclose tozero, henceits nameof0-it pulse. Thegroupvelocity ofa0-tpulse is close tothephase velocity oflight. Inanoptically denseabsorptive medium, theslowGaussian pulse andthefast 0-it pulse arewellseparated intimeandthey donotoverlap attheoutput oftheabsorber. Timegating ofthepromptpart of thepulse allows separating thenarrowspectrum, theslowpartofthepulse attheoutput. Suchafiltering isnotsensitive tothespectrum oftheinput pulse. Theparameters ofthenarrowspectrum pulse, i.e., thewidth, theshape andthetime of arrival, depend only ontheparameters ofthefilter, i.e., theeffective length oftheabsorber andthewidth oftheEIT window.