Two-component structure in the angular emission of a laser-produced Ta plasma

Thum, Andrea; Rupp, A.; Rohr, K

doi:10.1088/0022-3727/27/8/032

Cited by 25 publications

(20 citation statements)

References 21 publications

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“…We do not see a conclusive argument to attribute this substantially different result to the difference in the focal intensities of both experiments, which in the present case are one to two orders of magnitude larger. Although a higher laser intensity increases the relative amount of particles in the jet structure (Thum et al 1994), described by a larger value of the fitting parameter b, the total particle signal even at these higher intensities is determined by the dominating contribution of the neutral component (see the absolute particle numbers in figure 2).…”

Section: Resultsmentioning

confidence: 99%

“…Thereby it has already been clearly ascertained, in the proceeding experiments, that the emission profile indeed depends on the atomic mass A of the target and that in a cos n fit for the jet structure the exponent n can be approximated rather well by a A 1/2 function (Buttini et al 1998). As a second result it was shown, that the relative contribution of the steep part depends on the focal intensity of the laser and hence, via the plasma temperature, on the degree of ionization (Thum et al 1994). These measurements, which had been differential with respect to the number of neutrals and the differently charged ions, indicated that the angular distributions of the neutral particles and the ions are different.…”

Section: Introductionmentioning

confidence: 83%

“…These measurements, which had been differential with respect to the number of neutrals and the differently charged ions, indicated that the angular distributions of the neutral particles and the ions are different. Later Hansen et al (1997) even claimed, in an experiment where they measured the angular distribution of the totally emitted silver particles in a similar way to Thum et al (1994) together with the unresolved current signal that the 'peak of ejected particles along the normal is composed of the ions alone'. This is in contrast to results of Namiki et al (1991) where, by using a quadrupole mass spectrometer, a well developed peaked structure for the neutral particles alone was also measured.…”

Section: Introductionmentioning

confidence: 94%

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Angular emission distributions of neutrals and ions in laser ablated particle beams

Thum-Jager

Rohr

1999

J. Phys. D: Appl. Phys.

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The present work represents investigations of angular emission distributions in laser-produced particle beams resolved for the different ion groups (up to q = 4) and the neutral particle component. The measurements are for a spectrum of target masses: 12 C, 27 Al, 48 Ti, 59 Ni, 96 Mo and 181 Ta. The plasma was produced by obliquely incident Q-switched pulses (τ = 5 ns and λ = 1.06 µm) of a Nd-YAG laser focused to energy densities ranging from about 20 to 180 J cm −2 .For the first time the results reveal in detail that the emission distributions systematically depend on the degree of ionization of the particles in the cloud. While for the neutral particles the angular emission is always dominated by a broad background with an additional, but less pronounced, peaked component, the background component rapidly but continuously diminishes with the increasing charge state of the ions. If, in the usual way, the emission distribution is approximated by the superposition of a cosine and a cos n fit function, the distribution of ions with q 2 can already be well fitted by a cos n function alone. It seems highly probable, that this behaviour essentially is a result of the recombination dynamics during the expansion. It was found that the effect holds for all atomic masses investigated, whereby the mass dependence of the exponent n for all species behaves alike, approximately following a A 3/4 law.

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Section: Resultsmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 83%

Section: Introductionmentioning

confidence: 94%

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Angular emission distributions of neutrals and ions in laser ablated particle beams

Thum-Jager

Rohr

1999

J. Phys. D: Appl. Phys.

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“…Commonly the measured behaviour is discussed in terms of a cosine function for the background component and a cos n function for the peaked component. However, in spite of the many experiments so far (Venkatesan et al 1988, Neifeld et al 1988, Gorbonov and Konov 1990, Davanloo et al 1992, Sajjadi et al 1990, Champeaux et al 1993, Lichtenwalner et al 1993, Thum et al 1994, Hansen et al 1997, the picture seems confusing, since the cos n fits in those experiments give exponents n in the range 1-260. In particular, controversial results have been published concerning the dependence of the steep structure on the atomic mass M of the target.…”

Section: Introductionmentioning

confidence: 99%

The mass dependence of the jet formation in laser-produced particle beams

Buttini

Thum-Jager

Rohr

1998

J. Phys. D: Appl. Phys.

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The jet formation in laser-produced particle beams has been investigated as a function of the atomic mass of the target. The plasma was produced by an obliquely incident Q-switched pulse (τ = 5 ns and λ = 1.06 µm) of a Nd:YAG laser focused onto a relatively large area of about 5 × 10 −4 cm 2 at an energy density of 26 J cm −2 . Angular emission distributions of absolute particle numbers have been measured for 27 Al, 48 Ti, 59 Ni, 96 Mo, 108 Ag, 119 Sn and 181 Ta targets for identical laser-target conditions. It is found that the measured angular emission profile and the number of particles ablated depend systematically on the atomic mass M . If the angular behaviour is described as usual in terms of a two-component structure by the superposition of a smooth cosine-like background distribution and an additional steep emission structure which is approximated by a cos n function, it is found that the exponent n gradually increases on going from Al to Ta, closely following a M 1/2 fit. Since the degree of ionization of the expanding plasma is relatively low, the observed angular behaviour is essentially that of the neutral particles.

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“…However, the important intensity regime for UV lasers from 100 MW/cm 2 to 400 MW/cm 2 , in which the plume contains neutrals as well as ions, has been modelled with a two-dimensional treatment only by Schreiner and Urbassek [5]. A few measurements of the angular distribution of the emitted species from a single-component target exist [6]- [9], but none of them includes ions as well as neutrals in this intensity regime for UV lasers [10].…”

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confidence: 99%