Open AccessIntense femtosecond laser driven collimated fast electron transport in a dielectric medium–role of intensity contrast
Author(s) -
Indranuj Dey,
Amitava Adak,
Prashant Kumar Singh,
Moniruzzaman Shaikh,
Gourab Chatterjee,
Deep Sarkar,
Amit D. Lad,
G. Ravindra Kumar
Publication year - 2016
Publication title -
optics express
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.394
H-Index - 271
ISSN - 1094-4087
DOI - 10.1364/oe.24.028419
Subject(s) - femtosecond , laser , electron , materials science , optics , collimated light , shadowgraphy , plasma , picosecond , dielectric , atomic physics , physics , optoelectronics , quantum mechanics
Ultra-high intensity (> 10 18 W/cm 2 ), femtosecond (~30 fs) laser induced fast electron transport in a transparent dielectric has been studied for two laser systems having three orders of magnitude different peak to pedestal intensity contrast, using ultrafast time-resolved shadowgraphy. Use of a 400 nm femtosecond pulse as a probe enables the exclusive visualization of the dynamics of highest density electrons (> 7 × 10 21 cm -3 ) observed so far. High picosecond contrast (~10 9 ) results in greater coupling of peak laser energy to the plasma electrons, enabling long (~1 mm), collimated (divergence angle ~2°) transport of fast electrons inside the dielectric medium at relativistic speeds (~0.66c). In comparison, the laser system with a contrast of ~10 6 has a large pre-plasma, limiting the coupling of laser energy to the solid and yielding limited fast electron injection into the dielectric. In the lower contrast case, bulk of the electrons expand as a cloud inside the medium with an order of magnitude lower speed than that of the fast electrons obtained with the high contrast laser. The expansion speed of the plasma towards vacuum is similar for the two contrasts.