Wave packet dynamics in atoms and molecules Eva Heesel Corinne Glendinning Helen Fielding Department of Chemistry University College London UCL Progress Report at RAL Attomeeting on 07.12.2005
Interferometer and Ramsey Fringes Interferometer • Stabilisation program completed • Breadboard under investigation Ramsey Fringe Experiment • Filter for wavelength selection under way • Need kHz gas jet, TOF chamber, full beam line • Can generate high-order harmonics from each interferometer beam + observe fringes (XUV SPIDER -Oxford report). Can also characterise bandwidth.
Krypton experiment (Corinne) Use time-resolved photoelectron spectroscopy to look at low n Rydberg states • Excitation of Kr + 4s2 4p5(2P3/2) 6s, 7s and 5d Rydberg states from the ground state via 5p intermediate • A VUV pulse will then ionise the Kr core further or ionise the Rydberg electron • Relate different core excitations to core- Rydberg electron distances • Double ionisation of Kr core – opportunity to study the dynamics of the Rydberg electron in the presence of a doubly charged core • If photoelectrons are detected by imaging, the l- character of the Rydberg states can be reconstructed
Kr Energy levels 60 Kr++ 4s4p5(1P1) LIMIT 55.9499 Kr++(4s2 4p34 S)4d (5D0,1,2,3,4) LIMITS 55.5247, 55.5277, 55.5289, 55.5303,55.5498 50 Kr++ 4s4p5(3P2,1,0) LIMITS 52.7330, 53.1607, 53.4289 Kr++(1S0) LIMIT 42.4608 40 Kr++(1D2) LIMIT 40.1751 Kr++(3P2,1,0) LIMITS 38.3595, 38.92338, 39.01817 Energy (eV) 30 VUV HHG 20 Kr+(2P1/2) LIMIT 14.6654 800 nm Kr+(2P3/2) LIMIT 13.9996 10 ~6 fs Kr+ 4s24p5 (2P3/2)5d 2[7/2] J=3; 2[3/2] J=2,1; 2[5/2] J=2,3Kr+ 4s24p5 (2P1/2)6s 2[1/2] J=1; Kr+ 4s24p5 (2P3/2) 7s 2[3/2] J=2,1 (range 13.00- 13.11 eV) 214 nm OPA 0 1S0 Kr+ 4s24p5 (2P3/2) 5p2[3/2] J=2 11.5458
Two-stage plan for Kr experiment At UCL: Measure frequency-resolved spectrum • Narrowband: Use ns beams: 214 nm and 800 nm • Can do experiment both field-free and with static field (Stark splitting) • Photoionise Rydberg states with 400/800 nm photon • Field-free: apply field with 20 ns rise time to extract ions • With static field: investigate Stark shifts (good test for imaging) (detect electrons) At IC: Measure electron dynamics + image photoelectrons • Use 214 nm ns beam (OPO) and 200 nm fs beam (FHG from few-cycle pulse) • Need static field for imaging.
Benzene experiment (Eva) Monitor ultrafast dynamics of benzene molecule using time- resolved photo- electron spectroscopy • Excitation of benzene molecules from the ground state S0 to the S2 state with 200 nm photons (pulse duration as short as possible) • The S2state decays very fast (< 50 fs) by internal conversion to high vibrational levels of the S1 and S0 states. • Time-delayed probe photon (~ 50-100 eV) can ionise populations from all electronic states: Detect photoelectrons with different kinetic energy • Energy resolution given by a) pulse duration (bandwidth) - 0.35 eV for 5 fs pulse b) resolution of photoelectron spectrometer (1%)
Benzene Energy levels Energy (eV) VUV probe has the advantage of being able to ionise all intermediates and products I.P. 9.24 S2 6.02 S1 4.75 VUV (e.g. 50-100 eV) 200 nm (6.2 eV) S0
Plans/work in progress • Generation/Characterisation of 200 nm • Generation: Fourth-harmonic of 800 nm • Characterisation: cross-correlation, two-photon ionisation,…. • Calculations • Mike’s Robb group (IC chemistry) • Wave packet moves through conical intersection