Time of flight emission spectroscopy of laser produced nickel plasma: Short-pulse and ultrafast excitations

Abstract

We report the experimental investigation and comparison of the temporal features of short-pulse (7 ns) and ultrafast (100 fs) laser produced plasmas generated from a solid nickel target, expanding into a nitrogen background. When the ambient pressure is varied in a large range of 10 À6 Torr to 10 2 Torr, the plume intensity is found to increase rapidly as the pressure crosses 1 Torr. Time of flight (TOF) spectroscopy of emission from neutral nickel (Ni I) at 361.9 nm (3d 9 ( 2 D) 4p ! 3d 9 ( 2 D) 4s transition) reveals two peaks (fast and slow species) in short-pulse excitation and a single peak in ultrafast excitation. The fast and slow peaks represent recombined neutrals and un-ionized neutrals, respectively. TOF emission from singly ionized nickel (Ni II) studied using the 428.5 nm (3p 6 3d 8 ( 3 P) 4s! 3p 6 3d 9 4s) transition shows only a single peak for either excitation. Velocities of the neutral and ionic species are determined from TOF measurements carried out at different positions (i.e., at distances of 2 mm and 4 mm, respectively, from the target surface) on the plume axis. Measured velocities indicate acceleration of neutrals and ions, which is caused by the Coulomb pull of the electrons enveloping the plume front in the case of ultrafast excitation. Both Coulomb pull and laser-plasma interaction contribute to the acceleration in the case of short-pulse excitation. These investigations provide new information on the pressure dependent temporal behavior of nickel plasmas produced by short-pulse and ultrafast laser pulses, which have potential uses in applications such as pulsed laser deposition and laser-induced nanoparticle generation. V C 2014 AIP Publishing LLC. [http://dx.

Dynamics of neutrals and ions in an ultrafast laser produced Zn plasma

“…These measurements show that emission intensity maximizes within an optimum range of pressures (5 Torr-100 Torr in the present case) where it may be assumed that thermal leak to the surroundings is minimal and collisions among the plasma species is maximal. 22 This observation is in support of existing experimental results reported by Farid et al 23 and Smijesh et al 24 We also performed OTOF studies for 10 Torr, 50 Torr, and 100 Torr background pressures, for various axial positions in the expansion direction of the plume. The effects of pressure and position on the OTOF of neutrals at 481 nm and ions at 491 nm are presented in Secs.…”

“…12,22,24 For example, fast neutrals arrive within 100 ns to 200 ns, whereas slow neutrals arrive around 300 ns to 500 ns or more, at close distances to the target. 28 Moreover, it has been experimentally found that fast neutrals display a fast rise in the OTOF spectra compared to slow neutrals.…”

Diamagnetic cavitization of laser-produced barium plasma in transverse magnetic field

“…With an increase in the ambient gas pressure, the collisions between the ions and ambient gas increases, and large time delay is observed for the slow component, whereas the velocity of the fast component is unaffected. These results are in agreement with previous reports on the generation of LPP at larger irradiation fluences [18,19]. With a further increase in pressure (>10 −1 Torr), the interpenetration of the plume species and background gas is much less, and the plume species will compress the background gas.…”

“…The presence of ambient gas completely modified the velocity distributions of the ionic species in the plasma plume. At the intermediate Ar pressures of 10 −2 and 10 −1 Torr, the ionic profiles showed two components, designated as fast and slow as observed by several workers [17][18][19]. It is also observed that the fast component in case of 10 −2 and 10 −1 pressures arrive earlier than the ions recorded at 10 −5 Torr.…”

Acceleration of neutrals in a nanosecond laser produced nickel plasma

“…Rajeev et al 24 has reported a compact laser-driven plasma accelerator for high energy neutral beams, in which a laser accelerated ion is converted to an energetic neutral atom as a result of highly efficient electron transfer from Rydberg excited clusters. Similarly, our recent studies in ultrafast laser produced zinc and nickel plasmas 25,26 have indicated that fast neutrals indeed accelerate through a short distance along the expansion direction of the plume normal, to the ablation surface. Since the origin of this acceleration required a more detailed investigation, in the present work, we study in detail the occurrence of fast neutrals, their origin, and time of flight dynamics in an LPP generated by irradiating a solid nickel target using a nanosecond laser.…”