In:
Journal of Applied Physics, AIP Publishing, Vol. 109, No. 12 ( 2011-06-15)
Abstract:
Pulsed laser ablation of molecular solids is important for identification and quantification in (bio-)organic mass spectrometry, for example using matrix-assisted laser desorption/ionization (MALDI). Recently, there has been a major shift to using MALDI and related laser ablation/post-ionization methods at atmospheric pressure. However, the underlying laser ablation processes, in particular early plume formation and expansion, are still poorly understood. Here, we present a study of the early ablation processes on the ns-time scale in atmospheric pressure UV-laser ablation of anthracene as well as of different common MALDI matrices such as 2,5-dihydroxybenzoic acid (2,5-DHB), α-cyano-4-hydroxycinnamic acid and sinapinic acid. Material release as well as the formation and expansion of hemi-spherical shock waves were studied by shadowgraphy with high temporal resolution (∼5 ns). The applicability of the classical Taylor-Sedov model for expansion of strong shock waves (“point-blast model”), as well as the drag force model, were evaluated to mathematically describe the observed shock wave propagation. The time- and energy-dependent expansion of the shock waves could be described using a Taylor-Sedov scaling law of the form R ∝ tq, when a q-exponent of ∼0.5 instead of the theoretical value of q = 0.4 was found, indicating a faster expansion than expected. The deviations from the ideal value of q were attributed to the non-negligible influence of ambient pressure, a weak versus strong shock regime, and additional acceleration processes present in laser ablation that surpass the limit of the point-blast model. The onset of shock wave formation at a fluence of ∼15–30 mJ/cm2 for the compounds investigated coincides with the onset of bulk material release, whereas, pure desorption below this fluence threshold did not lead to features visible in shadowgraphy.
Type of Medium:
Online Resource
ISSN:
0021-8979
,
1089-7550
Language:
English
Publisher:
AIP Publishing
Publication Date:
2011
detail.hit.zdb_id:
220641-9
detail.hit.zdb_id:
3112-4
detail.hit.zdb_id:
1476463-5
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