1. Simon Hutchinson February 21 st 2012

2. What did they accomplish? “full electromagnetic transparency to XUV light in He can be achieved by destructively interfering two distinct multi-photon ionization pathways” 1.Electromagnetic transparency via quantum interference 2. Multi-photon ionization pathway – XUV + IR Helium Ip = 24.6 eV XUV IR 3. Results: Transparency and modulation of ionisation rate at twice the electromagnetic frequency of the IR pulse.

3. |1› |2› |3› Dressing field 1.Opposite phase 2.Same amplitude Creates coherent states and allows for quantum interference Electromagnetically Induced Transparency IMPORTANT FOR LATER

4. Assisted Ionisation Channels in Helium -24.59 eV 1s Continuum -3.63 eV2p Dressing Field -3.69 eV -6.84 eV Photon Energy Resultant Excitation 11 th Harmonic 17.05 to 18.19 eV -7.54 to -6.40 eV 13 th Harmonic 20.17 to 21.49 eV -4.42 to -3.10 eV 1. Coherence 2. Coupling 1. 2.

5. Control in the Experiment 1. XUV amplitude -XUV mirror coatings -Al filter (Total Ionization Channel Probability Amplitude) 2. XUV energy tuning -Phase-matching via pressure tuning

6. Control in the Experiment 3. Phases of interfering channels -Delay between IR dressing field and XUV pulses

7. The Experiment (part one) Using COLTRIMS, measure He + yield as the 13 th harmonic is scanned. (XUV at t0, IR x-axis) Enhancement for positive delays: transient (resonant?) multi-photon ionisation.

8. The Experiment (part two) Lifetime of 2p state in helium = 10ps Phys. Rev. A 28, 3340–3348 (1983)