Nonlinear optical phenomena

Transient light absorption induced in glassby femtosecond laser pulses

I. V. Blonskii^a, V. N. Kadan^a, O. I. Shpotyuk^b, I. A. Pavlov^a, N. N. Kryuchkov<sup>a

a</sup> Institute of Physics, National Academy of Sciences of Ukraine, Kiev
^b Karat Scientific and Production Enterprise, L'vov

Abstract: The dynamics of the transient light absorption induced in K8 optical glass by filamented femtosecond laser pulses have been studied using time-resolved transmitted-light microscopy at wavelengths from 450 to 700 nm. The transient absorption measured as a function of probe beam wavelength is compared to that predicted by the Drude plasma model. We conclude that, just 450 fs after a pump pulse, the transient absorption is dominated by transient electronic states, presumably, self-trapped excitons, with an excitation energy of 2.6 — 2.7 eV. These states are filled with free-carriers from a long-lived plasma, which acts as a "carrier reservoir". The relaxation of transient absorption has two components. The slow component, with τ₁ ~17-17.5 ps, is governed by the plasma thermalisation time, whereas the second, with τ₁ ≫ 300 ps, is determined by the plasma lifetime.

PACS: 42.60.Fc, 42.70.Nq, 42.65.Re

Received: 20.01.2009
Revised: 30.06.2009

 English version: Quantum Electronics, 2009, 39:10, 933–937

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