Transition from periodic lattice to solid plasma in ultrashort pulse irradiation of metals Dimitri Fisher Soreq NRC Israel 25 th Hirschegg PHEDM Workshop Jan 30 – Feb 04, 2005

Femtosecond laser irradiation of metals - 1 electron subsystem: ion (phonon) subsystem: laser energy deposition: S.I.Anisimov, B.L.Kapeliovich, T.L.Perel'man, JETP 39, (1974)

Femtosecond laser irradiation of metals - 2 D.V.Fisher, M. Fraenkel, Z. Henis, E. Moshe, S. Eliezer PRE 65, (2001).

Femtosecond laser irradiation of metals - 3 Typical regime: Approximations available: OK What at T e ~T F ???

Longitudinal momentum relaxation rate

electron-ion coupling mismatch element g metal (any T e ‘ T i ) [erg / cm 3 K s] g plasma (T e = 10 eV) [erg / cm 3 K s] g max (T e = 10 eV) [erg / cm 3 K s] Al 3.8× × ×10 19 Cu 6.1× × ×10 19

e-i coupling in NFE metal

e-i coupling in NFE metal - 2

e-i coupling in SCP Strongly - Coupled Plasma: Coulomb logarithm = 1 Maximal energy transfer regime:

What are the mechanisms of the gradual transition from metal to plasma electron behavior? Non-isochoric: –surface layer expansion; –(possibly) local breach of charge neutrality? Isochoric: –ultrafast melting (thermal or nonthermal); –ionization of localized electron states, charge-disordered solid regime; –electron localization due to e-e collisions?

Isochoric transition from metal to plasma behavior time scales: ultrafast melting: ~ fs (governed by forces and ion mass); charge disorder: ~ 1-10 fs (governed by electron impact ionization); electron localization: ~ 1 fs or shorter (governed by electron spread and velocity).

ORDERED SOLID CHARGE – DISORDERED SOLID Z = 2Z = 2.5Z = 3

Mg, Ca; Zn, Cd, Sn?, Pb?: charge disorder by ionization of core states No experimental evidence so far! The predictions are pure theory. Zn: localized 3d-states ~8 eV below Fermi level. Should ionize at modest electron temperatures, leading to charge disorder. Mg: L-shell ionization by electron impact. Must do ultrafast melting experiments!

s-band (2 states) d-band (10 states) Cu: outer shell: 11 electrons per atom Fermi level diagram from: Janak, Williams, and Moruzzi, Phys Rev B 11 p noble metals: charge disorder by d-band states localization

D.V.Fisher et. al.: proceedings XXVIII ECLIM, Rome, Sept. 2004

Results: theory vs. experiment

d-shell localization - 1 In this model: d-states localize as the d-band peak crosses the bottom of the conductivity band. Can localization occur at lower T e ? Yes it can. Band width ~ inverse tunneling time ( ~ 0.2 fs ). This is NOT related to d-shell hole lifetime with respect to recombination ( ~ fs ). INFERNO model underestimates band width, but we can trust the trend.

d-shell localization - 2

d-shell localization - 3

Experimental evidence: X.Y.Wang, D.M.Riffe, Y.-S.Lee, M.C.Downer, PRB 50, (1994) Two-pulse thermionic emission from gold targets shows significant increase in g at T e ~ 1eV  Phonon emission & absorption by d-band holes?  Onset of charge disorder?  Suprathermal electron contribution?  Photon energy is very close to d-shell absorption edge, so direct production of d-shell holes is possible! NB: Holes are short-lived with respect to tunneling between ion wells, but long-lived with respect to recombination. !!!

Aluminum: No charge disorder! L-shell lies too deep. Coupling g(T e,T i ) decreases in NFE model for T e >T F ! D.V.Fisher et.al. PRE 65 p (2001). Is electron localization in e-e collisions alone effective enough to bring g(T e,T i ) anywhere close to the Spitzer limit ??? Maybe not… Pseudopotentials for Al: all ions assumed identical. “Coupled mode” approach. Result: g(T e,T i ) < g met (T e,T i ) ??? M.W.C.Dharma-wardana and F.Perrot, PRE 63 p (2001). Melting: thermal B.J.Siwick et.al. Science 302 p.1382 (2003).

CONCLUSIONS: Fascinating physics is revealed, pertaining to both fundamental physics (quantum mechanics, electron properties of disordered systems) and to applications. Any experimental data are welcome!!! What happens at higher photon energies?!

THANKS: Zeev Zinamon Zohar Henis Shalom Eliezer Moshe Fraenkel Organizers!!!