Leisner Arne, Rohlfing Andreas, Röhling Ulrich, Dreisewerd Klaus, Hillenkamp Franz
Institute of Medical Physics and Biophysics, Westfälische Wilhelms-Universität Münster, Germany.
J Phys Chem B. 2005 Jun 16;109(23):11661-6. doi: 10.1021/jp050994l.
The dynamics of the expanding material plume after irradiation of a matrix sample with two different infrared (IR) lasers, an Er:YAG laser of ca. 100 ns and an optical parametric oscillator (OPO) laser system of 6 ns pulse duration, were investigated by imaging the plumes with nanosecond time resolution. Both lasers emitted at an identical wavelength of 2.94 microm. Laser exposure parameters were typical for infrared matrix-assisted laser desorption/ionization mass spectrometry (IR-MALDI-MS); glycerol was employed as a liquid matrix to provide a homogeneous sample and reproducible plume formation. A Nd:YAG laser (532 nm; 8 ns) was used as the illumination source and a CMOS camera with a ten-bit dynamic range served for recording of the images. Dark-field as well as scattered light illumination was employed to preferentially image the gaseous and particulate components of the plume, respectively. During the initial phase of its expansion (ca. 1 micros) the plume appears to consist of a continuous cloud of material of varying density. At later times after exposure, individual particles of several micrometers in size dominate the images. For both laser pulse durations material ejection was observed for times as long as 100 micros postexposure. Subtle but distinct differences in the plume dynamics are observed for the two different pulse durations. They are related to a transition between the regimes below and above acoustic confinement. The experimental findings are compared to results obtained in two previous studies by photoacoustic analysis of the desorption process and IR-laser postionization of the plume.
用纳秒时间分辨率对羽流进行成像，研究了用两种不同的红外（IR）激光照射基质样品后膨胀物质羽流的动力学，这两种激光分别是脉冲宽度约为100 ns的铒钇铝石榴石（Er:YAG）激光和脉冲持续时间为6 ns的光学参量振荡器（OPO）激光系统。两种激光均在2.94微米的相同波长下发射。激光曝光参数是红外基质辅助激光解吸/电离质谱（IR-MALDI-MS）的典型参数；甘油被用作液体基质，以提供均匀的样品并形成可重复的羽流。一台钕钇铝石榴石（Nd:YAG）激光（532 nm；8 ns）用作照明源，一台具有十位动态范围的互补金属氧化物半导体（CMOS）相机用于记录图像。分别采用暗场照明和散射光照明来优先对羽流的气态和颗粒成分进行成像。在羽流膨胀的初始阶段（约1微秒），羽流似乎由密度不同的连续物质云组成。在曝光后的后期，几微米大小的单个颗粒在图像中占主导地位。对于两种激光脉冲持续时间，在曝光后长达100微秒的时间内都观察到了物质喷射。对于两种不同的脉冲持续时间，在羽流动力学中观察到了细微但明显的差异。它们与声约束以下和以上区域之间的转变有关。将实验结果与之前两项通过解吸过程的光声分析和羽流的红外激光后电离获得的研究结果进行了比较。
