Temperature and centre-of-mass energy of ions emitted by laser-produced polyethylene plasma

Abstract

A deconvolution of time-resolved ion collector signals was used to determine the temperature and the centre-of-mass (COM) velocity of H + and C q+ (1 q 6) ions emitted from a polyethylene target irradiated by the 3rd harmonics (λ = 438 nm) of an iodine laser up to the laser-beam intensity value of about 2 × 10 16 W cm −2 . The intensity dependence of the COM energy for single charge-states is shown. A plasma block, which precedes the main ion group, is characterized. The properties of the main ion group are compared with those of fast ions produced by a CO 2 laser [1]. It is shown that the separation of peaks, i.e. their visualization in the time-resolved ion collector signal, can be characterized by the ratio of thermal velocity to COM velocity. The charge-state dependence of the COM velocity is discussed.

Revealing of hydrodynamic and electrostatic factors in the center-of-mass velocity of an expanding plasma generated by pulsed laser ablation

“…where it is assumed that the ion collector is located at a distance x = L from the target and the y, z directions are considered parallel to the target surface (Krása et al, 2007. Furthermore, v x = L/t, |dv x | = Ldt/t 2 , dv y = dy/t, dv z = dz/t and the detector size is dS = dzdy.…”

Generation of high currents of carbon ions with the use of subnanosecond near-infrared laser pulses

“…11 The separation of charges can start if the center-of-mass energy of ions is more than 50 times higher than the thermal energy for all the charge states ͑q Ն 2͒ generated. 12 Since the number of visible peaks in all the TOF spectra presented is higher than the number of the carbon charge states, there is reason to suppose that the ion emission proceeds from the repetitive outbursts. The occurrence of the ion outbursts can be elucidated by a correlation between the peaks of TOF spectra of carbon ions measured with the IC and CEA, as Fig.…”

“…Vice versa, the higher contrast of laser beam restrains the self-focusing in the preformed plasma, and the generation of fast ions must, therefore, be weaker, as it was observed in the case of polyethylene plasma produced with the third harmonics of the iodine laser as opposed to the fundamental harmonics. 12 FIG. 5.…”

Analysis of time-of-flight spectra of ions emitted from laser-generated plasmas

“…The second way of determination of the ion velocity distribution is based on a deconvolution of time-resolved IC signal (TOF spectra) with the use of an appropriate velocity distribution dN/dv (17)(18)(19).…”

“…As it was already demonstrated, the Kelly & Dreyfus function expressing the ion current (or possibly flux of neutrals) based on the shifted Maxwell-Boltzmann distribution (12,13) can be applied for a current analysis (17)(18)(19):…”