Optical and Spectroscopic Techniques
Spectroscopy is the most important method for gaining detailed information on the structure and dynamics of atoms and molecules. The essential criteria of any spectroscopic technique are the attainable spectral resolution and the sensitivity.
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Spectroscopy is the most important method for gaining detailed information on the structure and dynamics of atoms and molecules. The essential criteria of any spectroscopic technique are the attainable spectral resolution and the sensitivity. Since lasers have been introduced as coherent narrow-band, intense radiation sources, spectroscopy has seen impressive progress. With single-mode lasers the spectral resolution can be greatly increased and finer details, generally hidden within the Doppler width of spectral lines, can be resolved. The available high intensity of lasers allows nonlinear spectroscopic techniques and the possibility of generating ultra-short light pulses has opened access to studies of very fast dynamical processes, such as the breaking of chemical bonds or the time-resolved redistribution of energy pumped into molecules by the absorption of photons. In this first part we will concentrate on stationary methods of spectroscopy where the spectral resolution, the maximum achievable sensitivity and the development of optimum detectors are the main subjects.
13.1 Stationary Methods............................... 987 13.1.1 Absorption and Emission Spectroscopy, Laser-Induced Fluorescence ............................... 998 13.1.2 Laser Spectroscopy in Molecular Beams ...................... 999 13.1.3 Nonlinear Laser Spectroscopy......... 1003 13.1.4 Polarimetry and Ellipsometry ......... 1009 13.1.5 Optical Pumping and Double Resonance ................. 1011 13.2 Time-Resolved Methods ........................ 1012 13.2.1 Basic Principles ............................ 1012 13.2.2 Wavelength-Tunable Short Pulses .. 1013 13.2.3 Time-Resolved Spectroscopy .......... 1017 13.2.4 Coherent Time-Resolved Spectroscopy ............................... 1022 13.2.5 Applications of Short Laser Pulses... 1026 13.3 LIDAR ................................................... 1031 13.3.1 Introduction ................................ 1031 13.3.2 Instrumentation .......................... 1033 13.3.3 Atmospheric LIDAR Applications ..... 1035 13.3.4 LIDAR Monitoring of Condensed Targets.................... 1039 13.3.5 Unconventional LIDAR Applications. 1046 13.3.6 Discussion and Outlook ................. 1047 References .................................................. 1048
13.1 Stationary Methods Basic Principles of Spectroscopic Techniques All spectroscopic techniques can be classified into those suitable for absorption spectroscopy and others adapted to emission spectroscopy. Emission spectroscopy demands the population of excited states that can emit the radiation. This excitation can be achieved by collisions (examples are gas discharges where electron impact excitation is the main excitation mechanism, or hot gases, such as the atmospheres of stars, where collisions between atoms or ions populate excited states) or by photon absorption (e.g. laser-excited fluorescence). One important criterion for any spectroscopic techniques is its sensitivity, which is defined as the minimum detectable number of photons absorbed or
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