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Why is this paper interesting?

Why is this paper interesting?. Relevant to the groups active research Water is easily available in all phases -PACER measurements : D₂O/H₂O . Water. Simple Molecule: HOMO, HOMO-1, HOMO-2 all identical p-type orbitals O₂ is not so simplistic. HOMO - 2. HOMO separation;

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Why is this paper interesting?

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  1. Why is this paper interesting? • Relevant to the groups active research • Water is easily available in allphases • -PACER measurements : D₂O/H₂O

  2. Water • Simple Molecule: HOMO, HOMO-1, • HOMO-2 all identical p-type orbitals • O₂ is not so simplistic.... HOMO - 2 • HOMO separation; • compare to CO₂..... 3.7eV HOMO - 1 2.2eV HOMO 12.6eV

  3. HHG in Molecules • Electron wavepacket launched – orbital information • Propagation in continuum – phase accumulation • Dipole amplitudes interfere – phase & amplitude modulation

  4. Experiment To date: HHG in H₂O observed using: • 1) 800nm light with microdroplets • 2) 3.6μm light with liquid This paper: Results from HHG in gas-phase H₂O 800nm & 1300nm light Intensities ≥ Isat Harmonics: 39th at 800nm 91st at 1300nm MOLECULES ARE NOT ALIGNED FOR THIS PAPER

  5. Experimental Set-Up • HHG 800nm light - Produced: 50cm Semi-Infinite Gas Cell (SIGC) - SIGC: 150μm pinhole - Ti:SaphRegen Amp (~3.5mJ, 40fs, 100Hz) - Focussed: f = 75cm achromatic lens - 2mm uncoated fused SiO₂ window Flat field concave grating → MCP →(Phosphor Screen) →CCD

  6. Results • Note Xe cut-off points • Previous H₂O HHG work: Highest photon energy: ~42eV • This experiment: ~60eV • SIGC HHG efficiency: ~ • Extension of HHG cut off..... ? • (a) Xe: Cut off: 106.8eV ? • (a)H2O: Cut off: 107.2eV ?

  7. Results • Harmonic spatial profiles nearly Gaussian in shape • Not the case beyond H₂O saturation intensity • Distortion due to plasma formation? • Need good spatial mode: extract harmonic phase and • amplitude • Higher photon energies & better phase matching – • magnify suppression → extension of cut off harmonics

  8. Results • Xe and H₂O at 1300nm, I = • Cut off energies: ~87eV for H₂O ~60eV for Xe Extension allows study of electronic and geometric structure – multiorbital and multicentre interferences start to appear in spectra at higher energies

  9. Conclusions • HHG demonstrated in H₂O: 800nm: ~60eV 1300nm: ~87eV • Suppression of ionization shown to be due to orbital symmetry at tunnelling stage – comparing Xe and H₂O harmonics →Easy to align: study different orbital contribution to HHG HOMO separation supports this • Interesting prospects with H₂O within the QOLS group

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