학술논문
Two-photon absorption of soft X-ray free electron laser radiation by graphite near the carbon K-absorption edge
Document Type
article
Author
Lam, RK; Raj, SL; Pascal, TA; Pemmaraju, CD; Foglia, L; Simoncig, A; Fabris, N; Miotti, P; Hull, CJ; Rizzuto, AM; Smith, JW; Mincigrucci, R; Masciovecchio, C; Gessini, A; De Ninno, G; Diviacco, B; Roussel, E; Spampinati, S; Penco, G; Di Mitri, S; Trovò, M; Danailov, MB; Christensen, ST; Sokaras, D; Weng, TC; Coreno, M; Poletto, L; Drisdell, WS; Prendergast, D; Giannessi, L; Principi, E; Nordlund, D; Saykally, RJ; Schwartz, CP
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Abstract
We have examined the transmission of soft X-ray pulses from the FERMI free electron laser through carbon films of varying thickness, quantifying nonlinear effects of pulses above and below the carbon K-edge. At typical of soft X-ray free electron laser intensities, pulses exhibit linear absorption at photon energies above and below the K-edge, ∼308 and ∼260 eV, respectively; whereas two-photon absorption becomes significant slightly below the K-edge, ∼284.2 eV. The measured two-photon absorption cross section at 284.18 eV (∼6 × 10−48 cm4 s) is 7 orders of magnitude above what is expected from a simple theory based on hydrogen-like atoms - a result of resonance effects.