Exploring femtosecond laser ablation in single-particle aerosol mass spectrometry
Exploring femtosecond laser ablation in single-particle aerosol mass spectrometry
复制标题
DOI：
10.5194/amt-11-4345-2018
复制
发表时间：
2017-10
影响因子：
3.8
通讯作者：
Ramakrishna Ramisetty;A. Abdelmonem;Xiaoli Shen;H. Saathoff;T. Leisner;C. Mohr
中科院分区：
文献类型：
--
作者：
Ramakrishna Ramisetty;A. Abdelmonem;Xiaoli Shen;H. Saathoff;T. Leisner;C. Mohr
抽象的。单个气溶胶粒子的大小、组成和混合状态可以使用单粒子质谱法（SPMS）进行真实的实时分析。在SPMS中，激光烧蚀是用于颗粒组分的解吸和电离的最广泛使用的方法，通常在一个步骤中实现两者。准分子激光器非常适合这项任务，因为它们在紫外（UV）波长下具有相对较高的功率密度（107-1010 W cm-2）（ns脉冲）和较短的触发时间。然而，不同的颗粒光学性质和基质效应使得这种分析方法的定量解释具有挑战性。在大气SPMS应用中，这既影响被烧蚀的单个颗粒的质量分数，也影响烧蚀材料的所得质谱碎裂模式。本研究探讨了使用较短的（飞秒，fs）激光脉冲的大气SPMS。它的目的是评估是否更高的激光功率密度的fs激光导致更完全的电离的整个粒子和更高的离子信号，从而提高SPMS的定量能力。我们系统地研究了功率密度和脉冲持续时间对空气中颗粒（聚苯乙烯乳胶，二氧化硅，硝酸铵，氯化钠，和定制的核壳颗粒）消融和质谱特征的再现性的影响。我们使用激光烧蚀气溶胶飞行时间单粒子质谱仪（LAAPTOF，AeroMegt GmbH），最初配备有准分子激光器（波长193 nm，脉冲宽度8 ns，脉冲能量4 mJ），并将其耦合到fs激光器（Spectra Physics Solstice-100 F超快激光），脉冲能量相似，但波长更长（266 nm，100 fs和0.2 mJ，800 nm，100 fs和3.2 mJ）。我们成功地将自由发射飞秒激光器与单粒子质谱仪耦合，利用粒子散射的飞秒激光触发质谱采集。一般来说，质谱显示离子强度随激光功率密度（109至1013 W cm-2）从ns到fs激光的增加而增加（1至5倍）。同时，飞秒激光烧蚀产生的光谱具有较大的离子碎片和离子团簇以及含氧的团簇，与纳秒激光烧蚀相比，这并没有使光谱解释更简单。飞秒激光的高功率密度导致更完全的粒子烧蚀和电离的想法在这项研究中不能得到证实。由于粒子的不完全电离，消融材料的定量仍然很困难。此外，fs激光器应用仍然受到在有用的时间范围内触发它的限制。需要进一步的研究来测试飞秒激光烧蚀在SPMS中的潜在优势。
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 (107–1010 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 is ablated, as well as the resulting mass spectral fragmentation pattern of the ablated material. The present study explores the use of shorter (femtosecond, fs) laser pulses for atmospheric SPMS. Its objective is to assess whether the higher laser power density of the fs laser leads to a more complete ionization of the entire particle and higher ion signal and thus improvement in the quantitative abilities of SPMS. We 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 3.2 mJ). We successfully coupled the free-firing fs laser with the single-particle mass spectrometer employing the fs laser light scattered by the particle to trigger mass spectra acquisition. Generally, mass spectra exhibit an increase in ion intensities (factor 1 to 5) with increasing laser power density (∼ 109 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. The idea that the higher power density of the fs laser leads to a more complete particle ablation and ionization could not be substantiated in this study. 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 time frame. Further studies are needed to test potential advantages of fs- over ns-laser ablation in SPMS.