Field ionization laser spectroscopy

In atomic laser spectroscopy, the laser radiation, which is tuned to a strong dipole transition of the atoms under investigation, penetrates the volume of species evaporated from the sample. The presence of analyte atoms can be measmed by means of the specific interaction between atoms and laser photons, such as by absorption techniques (laser atomic absorption spectrometry, LAAS), by fluorescence detection (laser-induced fluorescence spectroscopy, LIFS), or by means of ionization products (electrons or ions) of the selectively excited analyte atoms after an appropriate ionization process (Figures lA and IB). Ionization can be achieved in different ways (1) by interaction with an additional photon of the exciting laser or of a second laser (resonance ionization spectroscopy, RIS, or resonance ionization mass spectrometry, RIMS, respectively, if combined with a mass detection system) (2) by an electric field applied to the atomization volume (field-ionization laser spectroscopy, FILS) or (3) by collisional ionization by surrounding atoms (laser-enhanced ionization spectroscopy, LEIS). 

LEIS laser-enhanced ionization spectroscopy FILS field ionization laser spectroscopy RIS resonance ionization spectroscopy RIMS resonance ionization mass spectrometry... 

During the last decade, processing of polymers has become an important field of applied and fundamental research [48]. One of the most important fields is laser ablation involving various techniques and applications. Laser ablation is used as an analytical tool for MALDI (matrix-assisted laser de-sorption/ionization) [28, 29] and LIBS (laser-induced breakdown spectroscopy) [49] or as a preparative tool for PLD (pulsed laser deposition) of inorganic materials [37] and of synthetic polymer films [50, 51]. Another application is surface modification of polymers [52] if low fluences are applied, the polymer surface can be either chemically modified to improve adhesion... 

There are several methods of ionizing organic materials such as particle bombardment, chemical and field ionization, electron impact, field desorption, and laser pulse. For example, in the laser micro-mass analysis method, a laser pulse is used to supply the necessary energy to volatilize a sample from the surface for mass spectroscopy. 1 1 Mass spectrometry is often used in conjunction with gas chromatography to identify the separated components. The working technology of mass spectrometry is quite complex. 

Two types of time resolved experiments can be carried out on such a system. The less ambiguous approach is that employed in the stilbene—He study (fig. 10.5) in which a second laser, time delayed from the pump laser, is used to excited the state. Smith and Knee (1993) have used picosecond time resolved TPES spectroscopy in which zero-energy electrons are collected as a function of the probe laser wavelength. [Laser based TPES has also been called zero kinetic energy (ZEKE) electron spectroscopy or pulsed field ionization (PFI) (Muller-Dethlefs and Schlag, 1991)]. Figure... 

The Stark splitting and the field ionization of very high Rydberg levels provide sensitive indicators for measuring weak electric fields. These few examples demonstrate the variety of information obtained from Rydberg state spectroscopy. More examples can be found in Sect. 9.5 and in the literature on laser spectroscopy of Rydberg states [593-597]. 

LASER-BASED PULSED FIELD IONIZATION-ZERO ELECTRON KINETIC ENERGY PHOTOELECTRON SPECTROSCOPY... 

Since in densely populated industrial areas air and water pollution has become a serious problem, the study of pollutants and their reactions with natural components of our environment is urgently needed [15.75]. Various techniques of laser spectroscopy have been successfully employed in atmospheric and environmental research direct absorption measurements, laser-induced fluorescence techniques, photoacoustic detection, spontaneous Raman scattering and CARS (Chap. 8), resonant two-photon ionization, and many more of the sensitive detection techniques discussed in Chap. 6 can be applied to various environmental problems. This section illustrates the potential of laser spectroscopy in this field by some examples. 

Detection of microwave transitions via fluorescence becomes more and more difficult with increasing principal quantum number n of the level under study, since the oscillator strength of an optical transition from a level with n to a lower level decreases as n. The field ionization technique therefore favorably replaces fluorescence detection for large principal quantum numbers. Laser-microwave spectroscopy combinedwith field ionization was first realized by Gallagher et and by Fabre et aL Two-step... 

The inherent resolution of collinear-beam spectroscopy is still limited by the residual Doppler broadening. In beams with a broad velocity distribution the labeling of one velocity class by optical pumping, probed in a second Doppler-tuning zone, was exploited already before narrow Doppler widths were achieved. The complete elimination of the first-order Doppler effect in resonant two-photon absorption on Ne I has been discussed in Section 3.3, in connection with a precision measurement of the relativistic Doppler effect. A similar experiment was performed on In I, where the 29p Rydberg state was excited from 5p Pi/2 via 6s Si/2 and detected by field ionization. The linewidth caused by the laser jitter can be reduced to the transit-time limit of a few hundred kilohertz. 

C.-G. Wahlstrom Time-resolved X-ray spectroscopy of optical-field-ionized plasmas. Laser Part. Beams 13, 459 (1995)... 

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