Ultrafast Spectroscopy

Transcription

1 IPT Seleced Toics in Ulrfs Oics Ulrfs Secroscoy Chen-Bin Robin Hung Insiue of Phoonics Technologies Nionl Tsing Hu Universiy, Tiwnn Good references: Good references: P. Hnnford, Femosecond Lser Secroscoy Sringer, 005 S. Mukmel, Princiles of Nonliner Oicl Secroscoy Oxford, 1995

2 Why ulrfs secroscoy? Mos evens h occur in oms nd molecules occur on s or fs ime scles Fluorescence occurs on ns ime scle, bu comeing nonrdiive rocesses lwys seed hings u: ex fl nr Biologiclly imorn rocesses uilize exciion energy for uroses oher hn fluorescence nd hence mus be very fs. Collisions in room-emerure liquids occur on few-fs fs ime scle, so nerly ll rocesses in liquids re ulrfs. Semiconducor rocesses of echnologicl ineres re necessrily ulrfs or we wouldn be ineresed. Couresy of Prof. R. Trebino GIT

3 Ulrfs secroscoy: how? Ulrfs lser secroscoy involves sudying ulrfs evens h ke lce in medium using ulrshor ulses nd delys for ime resoluion. I usully involves exciing he medium wih one or more ulrshor lser ulses nd robing i vrible dely ler wih noher. Medium under sudy Exciion ulses Signl ulse Vribly delyed Probe ulse Signl uls se energy Dely The nl ulse energy or chnge in energy is loed vs. dely. The exerimenl emorl resoluion is he ulse lengh. Couresy of Prof. R. Trebino GIT 3

4 Wh re we mesuring? The um ulse excies molecules ino excied ses, which chnges he medium s bsorion coefficien nd refrcive index. Unexcied medium Unexcied medium bsorbs hevily wvelenghs corresonding o rnsiions from ground se. Excied medium bsorbs wekly wvelenghs corresonding o rnsiions ii from ground se. Excied medium The excied ses only live for finie ime his is he quniy we d like o find!, so he bsorion nd refrcive index recover. Couresy of Prof. R. Trebino GIT 4

5 The 1999 Nobel Prize in Chemisry Prof. A. H. Zewil ClTech used ulrfs-lser echniques o sudy how oms in molecule move during chemicl recions. 5

6 Pum-robe: schemics Princile Excie he smle wih one ulse Probe i wih noher vrible dely ler Mesuring he chnge in rnsmied robe ulse verge ower vs. dely Degenere e vs. non-degenere e Excie ulse R R 0 R E um - Smle medium E, Vrible dely, E robe Probe ulse Slow, Poin-deecor! Couresy of Prof. R. Trebino GIT 6

7 Meril roeries robed Trnsmission, refleciviy Fluorescence yield of riculr se Refrcive index Self-focusing, rnsien gring. Dichroism nd birefringence Polrizion deenden bsorion nd refrcive index Coheren vibrions Rmn shif, ime-vrying index chnge. Srucurl behvior Lser meling, lice chnge. 7

8 Degenere um-robe Almos idenicl o uo/cross-correlion seus Slow inegred deecion Time resoluion? Choer Chnges induced by he sronger um mesured A. M. Weiner, Ulrfs Oics Wiley

9 Non-degenere um-robe Probe is secrl brodened Mesuremen yields D d se Time-resolve AND secrlly-resolved Richer informion Differenil rnsmission secr A. M. Weiner, Ulrfs Oics Wiley

10 Time-resolved fluorescence secroscoy Pum ulse generes fluorescence Ging ulse wih vrible dely Ging imlemened using SFG Time-deenden energy disribuion Excie ulse Fluorescence Smle SFG crysl Slow deecor Probe ulse Lens Dely Fluo orescen be m ower Dely Couresy of Prof. R. Trebino GIT 10

11 Degenere um-robe Theoreicl derivion Co-olrized um nd robe 0 d' I ' h ' Negive n used o denoe surion in bsorion E z L 0 ou E E E z 0 e E z 0[1 L] Now ssume E E r, Re{ r, R{ Re{ e e j k 0 r j k 0 } r } 11

12 Degenere um-robe } Re{ } ] [ { r k r k j j e e L E } Re{ } 1 { g ou e e L E { * } j d h k k r ' ' { ' ' [ ' * '..]} j d h e cc k k r Deeced nl ' ' ' ' Re r k j e h d L L ' ' * ' ' Re r k j e h d L 0 1

13 Degenere um-robe The chnge in robe energy 0 L U 1 L[ ] Surion erm d d ' h ' ' d h di I ' ' ' h G 13

14 Degenere um-robe Coheren couling erm Trnsien bsorion gring 0 L U 1 L[ ] 1 d d h c c A symmeric funcion * ' ' ' * '.. A. M. Weiner, Ulrfs Oics Wiley

15 Degenere um-robe Slow bsorion recovery d * h se funcion Overshoo nd recovery: no meril resonse! A. M. Weiner, Ulrfs Oics Wiley

16 Degenere um-robe Co-olrized um-robe exerimenl d Cresyl viole dye 7 s ulse Absorion ~ se funcion Trnsform-limied Highly chired A. M. Weiner, Ulrfs Oics Wiley

17 Degenere um-robe Orhogonl um-robe Coheren couling: orienionl grings Sil modulion of olrizion ses Relive hses beween um nd robe fields A. M. Weiner, Ulrfs Oics Wiley

18 Trnsien orienion grings You migh hink h gring cn be induced only by sinusoidl inensiy ern cused by he inerference of wo rllel- olrized bems. Bu orhogonlly olrized bems, which h hve consn inensiy vs. osiion, lso induce gring! An orienion gring. Vriion of he elecric field vs. osiion: Orienion grings cn lso decy due o orienionl relxion. Couresy of Prof. R. Trebino GIT 18