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1、LETTERdoi:10.1038/nature11339Room-temperaturesolid-statemaser122MarkOxborrow,JonathanD.Breeze&NeilM.AlfordTheinventionofthelaserhasresultedinmanyinnovations,andparamagneticions,forexampleruby,thatismaintainedtypically8,13thedevicehasbecomeubiquitous.However,themaser,whic
2、hbelow10Kandexposed(withexceptions)toastrongd.c.magneticamplifiesmicrowaveradiationratherthanvisiblelight,hasnotbiasfield.Despitetheinconvenienceoftheseoperatingconditions,ashadaslargeanimpact,despitebeinginstrumentalinthelaser’swellascompetitionfromamplifiersbasedoncool
3、edhigh-electron-1,215birth.Themaser’srelativeobscurityhasmainlybeenduetothemobilitytransistors(HEMTs),rubymasersareusedindeep-space6inconvenienceoftheoperatingconditionsneededforitsvariouscommunications.Theywereused,forexample,byNASAtoreceive34realizations:atomicandfree-
4、electronmasersrequirevacuumimagesoftheSolarSystem’souterplanetsandtheirmoonsfromthe516chambersandpumping;andsolid-statemasers,althoughtheyVoyagerspaceprobes.6excelaslow-noiseamplifiersandareoccasionallyincorporatedThelowest-noisesemiconductor-basedamplifiersatmicrowave7,
5、815inultrastableoscillators,typicallyrequirecryogenicrefrigera-frequencies,whichtodaymostoftenincorporatecooledHEMTs,tion.Mostrealizationsofmasersalsorequirestrongmagnets,sufferfromaparticularlimitation.Oncooling,theHEMTamplifier’smagneticshieldingorboth.Overcomingthesev
6、ariousobstaclesresidualnoisetemperature,althoughlowenoughformanyapplica-17wouldpavethewayforimprovementssuchasmore-sensitivetions,isdifficulttoreducebelowafewkelvin.Althoughthis‘HEMT18chemicalassays,more-precisedeterminationsofbiomolecularplateau’canbeloweredsomewhatbyus
7、inglowerdevicepowers,itstructureandfunction,andmore-accuratemedicaldiagnosticshasmotivatedthesuccessfuldevelopmentofamplifiersbasedonres-17(includingtomography)basedonenhancedmagneticresonanceonantsuperconductinginterferencedevices,whichoffersubstan-9spectrometersincorpo
8、ratingmaseramplifiersandoscillators.tiallylowernoisetemperatures,albeitovermorelimitedbandwidths.Herewe
