CC BY
11LMI-I-20
Dynamics of water ionization under intensive femtosecond irradiation
V. Konov1, V. Kononenko1, V. Gololobov1
1General Physics Institute, Natural Sciences Center, Moscow, Russian Federation
Temporal variation of water optical properties (transmittance T and refractive index n) induced by intense 100 fs pulses of Ti:Sa (X=800 nm) laser was studied. Beam intensity ~1012 W/cm2 was sufficient for strong multi-photon ionization of water. For focal area visualization as well as measurements of n(t) and T(t), pump-probe interferometric technique was applied (Fig.1).
In contrast to our similar investigations with solids and gases no negative refractive index values, determined by free careers generation, could be monitored.
During the laser pulse action this effect can be explained by the fast (<100 fs) drop of free carriers concentration caused by solvation process. At the same time Kerr effect, resulting in positive growth of n(t), is strong both in the original and solvatized water. In the latter case the observed higher n(t) amplitude can be explained by higher non-linear properties of solvatized water and by self-focusing of the laser beam.
After pulse termination non-monotonous behavior of n(t) was found. Two additional peaks with An=4*10-3 and 6*10-3 at 3 ps and 1ns delay times are clearly seen in Fig.1b. We consider this effect is determined by a combination of solvatized electrons interaction with water molecules and thermodynamic phenomena.
This work was supported by RSF grant N 19-12-00255.
260 fs
420 fs
3900 fs
144566 fs
1487900 fs
a) 20 ftm
Fig.1. Modification of water optical properties during and after fs pulse action a) Snapshots with marked delays b) Dynamics of transmittance and refractive index
