Kupita patsogolo kwa ukadaulo wogwiritsa ntchito kuwala kwa ultraviolet kwambiri

Kupita patsogolo mu ultraviolet yoopsaukadaulo wa gwero la kuwala

M'zaka zaposachedwapa, magwero amphamvu kwambiri a ultraviolet okhala ndi harmonic ambiri akoka chidwi chachikulu m'munda wa mphamvu za ma elekitironi chifukwa cha mgwirizano wawo wamphamvu, nthawi yochepa ya kugunda kwa mtima komanso mphamvu yayikulu ya photon, ndipo agwiritsidwa ntchito m'maphunziro osiyanasiyana a spectral ndi kujambula. Ndi kupita patsogolo kwa ukadaulo, izigwero la kuwalaikupita patsogolo kufika pa kuchuluka kwa ma frequency obwerezabwereza, kuchuluka kwa photon flux, mphamvu ya photon yambiri komanso kutalika kwafupikitsa kwa kugunda kwa mtima. Kupita patsogolo kumeneku sikuti kumangowonjezera kulondola kwa muyeso wa magwero a kuwala kwa ultraviolet kwambiri, komanso kumapereka mwayi watsopano wamtsogolo wa chitukuko chaukadaulo. Chifukwa chake, kuphunzira mozama ndikumvetsetsa gwero la kuwala kwa ultraviolet kobwerezabwereza kwambiri ndikofunikira kwambiri pakuphunzitsa ndikugwiritsa ntchito ukadaulo wamakono.

Pa kuyeza kwa ma electron spectroscopy pa femtosecond ndi attosecond time scale, kuchuluka kwa zochitika zomwe zimayesedwa mu beam imodzi nthawi zambiri sikokwanira, zomwe zimapangitsa kuti magwero a kuwala kobwerezabwereza kochepa asakwanire kupeza ziwerengero zodalirika. Nthawi yomweyo, gwero la kuwala lomwe lili ndi flux yotsika ya photon lidzachepetsa chiŵerengero cha chizindikiro-ku-phokoso cha kujambula kwa microscopic panthawi yochepa yowonekera. Kudzera mu kufufuza kosalekeza ndi kuyesa, ofufuza apanga kusintha kwakukulu pakukonza ndi kupanga kutumiza kwa kuwala kwa ultraviolet kobwerezabwereza kwambiri. Ukadaulo wapamwamba wowunikira ma spectral pamodzi ndi gwero la kuwala kwa ultraviolet kobwerezabwereza kwambiri kwagwiritsidwa ntchito kuti akwaniritse kuyeza kolondola kwambiri kwa kapangidwe ka zinthu ndi njira zamagetsi zamagetsi.

Kugwiritsa ntchito magwero a kuwala kwa ultraviolet koopsa, monga kuyeza kwa angular resolved electron spectroscopy (ARPES), kumafuna kuwala kwa ultraviolet koopsa kuti kuunikire chitsanzocho. Ma electron omwe ali pamwamba pa chitsanzocho amasangalatsidwa ndi kuwala kwa ultraviolet koopsa, ndipo mphamvu ya kinetic ndi emission Angle ya ma photoelectron imakhala ndi chidziwitso cha kapangidwe ka gulu la chitsanzocho. Chowunikira ma electron chokhala ndi ntchito ya Angle resolution chimalandira ma photoelectron owala ndikupeza kapangidwe ka gulu pafupi ndi gulu la valence la chitsanzocho. Kuti mupeze kuwala kwa ultraviolet kotsika kwambiri, chifukwa pulse yake imodzi ili ndi ma photon ambiri, idzasangalatsa ma photoelectron ambiri pamwamba pa chitsanzocho munthawi yochepa, ndipo kuyanjana kwa Coulomb kudzabweretsa kufalikira kwakukulu kwa mphamvu ya photoelectron kinetic, yomwe imatchedwa space charge effect. Kuti muchepetse mphamvu ya space charge effect, ndikofunikira kuchepetsa ma photoelectron omwe ali mu pulse iliyonse ndikusunga flux yokhazikika ya photon, kotero ndikofunikira kuyendetsalaserndi ma frequency ambiri obwerezabwereza kuti apange gwero la kuwala kwa ultraviolet kwambiri ndi ma frequency ambiri obwerezabwereza.

Ukadaulo wowonjezera wa resonance cavity umapangitsa kuti pakhale ma harmonics apamwamba kwambiri pafupipafupi pa MHz.
Pofuna kupeza kuwala kwa ultraviolet kochuluka kwambiri komwe kumabwerezabwereza mpaka 60 MHz, gulu la Jones ku University of British Columbia ku United Kingdom linachita kupanga kwa harmonic yapamwamba kwambiri mu femtosecond resonance enhancement cavity (fsEC) kuti lipeze kuwala kwa ultraviolet kochuluka kwambiri ndipo linagwiritsa ntchito pa kuyesa kwa angular resolved electron spectroscopy (Tr-ARPES) komwe kumakonzedwa nthawi. Gwero la kuwalali limatha kupereka flux ya photon yoposa 1011 photon numbers pa sekondi ndi harmonic imodzi pa liwiro lobwerezabwereza la 60 MHz mu mphamvu ya 8 mpaka 40 eV. Anagwiritsa ntchito njira ya ytterbium-doped fiber laser ngati gwero la mbewu ya fsEC, ndipo analamulira makhalidwe a pulse kudzera mu kapangidwe ka laser kapadera kuti achepetse phokoso la carrier envelope offset frequency (fCEO) ndikusunga makhalidwe abwino a pulse compression kumapeto kwa unyolo wa amplifier. Kuti akwaniritse kukhazikika kwa resonance mkati mwa fsEC, amagwiritsa ntchito malupu atatu owongolera ma servo kuti azitha kulamulira mayankho, zomwe zimapangitsa kuti azikhala olimba pa madigiri awiri a ufulu: nthawi yobwerera ndi kubwerera ya pulse cycle mkati mwa fsEC ikugwirizana ndi nthawi ya laser pulse, ndi kusintha kwa gawo la chonyamulira magetsi poyerekeza ndi pulse envelopu (monga, carrier envelopu phase, ϕCEO).

Pogwiritsa ntchito mpweya wa krypton ngati mpweya wogwirira ntchito, gulu lofufuza linapanga ma harmonics apamwamba mu fsEC. Anayesa Tr-ARPES muyeso wa graphite ndipo anaona kutenthetsa kwachangu komanso kubwereranso pang'onopang'ono kwa ma electron omwe sanasangalale ndi kutentha, komanso mphamvu za ma electron omwe sanasangalale ndi kutentha pafupi ndi mulingo wa Fermi pamwamba pa 0.6 eV. Gwero la kuwala ili limapereka chida chofunikira pophunzira kapangidwe ka zamagetsi ka zinthu zovuta. Komabe, kupanga ma harmonics apamwamba mu fsEC kuli ndi zofunikira kwambiri pakuwunikira, kugawa bwino, kusintha bwino kutalika kwa cavity ndi kutseka kwa synchronization, zomwe zidzakhudza kwambiri kukulitsa kwa cavity yolimbikitsidwa ndi resonance. Nthawi yomweyo, yankho la nonlinear phase la plasma pamalo oyambira a cavity ndi vuto. Chifukwa chake, pakadali pano, mtundu uwu wa gwero la kuwala sunakhale ultraviolet yayikulu kwambiri.gwero la kuwala kwa harmonic.