Introduction

Abstract

By spectroscopy we usually mean experimental charting of the energy-level structure of physical systems. For that purpose, the transition processes, spontaneous or induced, between different energy states are studied and spectroscopy therefore normally means analysis of various types of radiation — electromagnetic or particle emission. Spectroscopic investigations can be of a fundamental or an applied nature. In fundamental spectroscopy experimentally determined energy levels, transition probabilities, etc. are employed for obtaining an understanding of the studied systems using adequate theories or models. Usually, certain primary quantities (wavelengths, intensities, etc.) are measured in spectroscopic investigations. These quantities are then used to evaluate more fundamental quantities. This process is schematically illustrated in Fig. 1.1.