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https://doi.org/10.5194/amt-2017-357
© Author(s) 2017. This work is distributed under
the Creative Commons Attribution 4.0 License.
Research article
10 Oct 2017
Review status
This discussion paper is a preprint. It is a manuscript under review for the journal Atmospheric Measurement Techniques (AMT).
Exploring femtosecond laser ablation in single particle aerosol mass spectrometry
Ramakrishna Ramisetty1, Ahmed Abdelmonem1, Xiaoli Shen1, Harald Saathoff1, Thomas Leisner1, and Claudia Mohr1,2 1Institute of Meteorology and Climate Research, Karlsruhe Institute of Technology, Germany
2Department of Environmental Science and Analytical Chemistry, Stockholm University, Sweden
Abstract. Size, composition, and mixing state of individual aerosol particles can be analysed in real time using single particle mass spectrometry (SPMS). In SPMS, laser ablation is the most widely used method for desorption and ionization of particle components, often realizing both in one single step. Excimer lasers are well suited for this task due to their relatively high power density (107 W cm−2–1010 W cm−2) in nanosecond (ns) pulses at ultraviolet (UV) wavelengths, and short triggering times. However, varying particle optical properties and matrix effects make a quantitative interpretation of this analytical approach challenging. In atmospheric SPMS applications, this influences both the mass fraction of an individual particle that gets ablated, as well as the resulting mass spectral fragmentation pattern of the ablated material. The goal of the present study is to explore the use of shorter (femtosecond, fs) laser pulses for atmospheric SPMS, and to systematically investigate the influence of power density and pulse duration on airborne particle (polystyrene latex, SiO2, NH4NO3, NaCl, and custom-made core-shell particles) ablation and reproducibility of mass spectral signatures. We used a laser ablation aerosol time-of-flight single particle mass spectrometer (LAAPTOF, AeroMegt GmbH), originally equipped with an excimer laser (wavelength 193 nm, pulse width 8 ns, pulse energy 4 mJ), and coupled it to an fs-laser (Spectra Physics Solstice-100F ultrafast laser) with similar pulse energy, but longer wavelengths (266 nm with 100 fs and 0.2 mJ, 800 nm with 100 fs and 4 mJ, respectively). Generally, mass spectra exhibit an increase in ion intensities (factor 1 to 5) with increasing laser power density (~ 108 W cm−2 to ~ 1013 W cm−2) from ns- to fs-laser. At the same time, fs-laser ablation produces spectra with larger ion fragments and ion clusters, as well as clusters with oxygen, which does not render spectra interpretation more simple compared to ns-laser ablation. Quantification of ablated material remains difficult due to incomplete ionization of the particle. Furthermore, the fs-laser application still suffers from limitations in triggering it in a useful timeframe. Further tests are needed to test potential advantages of fs- over ns-laser ablation in atmospheric SPMS.

Citation: Ramisetty, R., Abdelmonem, A., Shen, X., Saathoff, H., Leisner, T., and Mohr, C.: Exploring femtosecond laser ablation in single particle aerosol mass spectrometry, Atmos. Meas. Tech. Discuss., https://doi.org/10.5194/amt-2017-357, in review, 2017.
Ramakrishna Ramisetty et al.
Ramakrishna Ramisetty et al.
Ramakrishna Ramisetty et al.

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