In every measuring system or optical instrument, the light source and its characteristics are of vital importance. The choice of source is based purely on its usefulness in optics: central wavelength, spectrum width, degree of coherence, polarization, optical power, impulse or continuous regime, etc. but also according to other, electrical or mechanical, criteria: current, electrical power, dimensions, etc.
Sources are used:
– for lighting: microscope stages, visualization systems, etc.;
– as an integral part of the measuring system: LIDAR, interferometer, confocal microscope;
– for light supply in a system: spectroscopy, communications, 3D imaging, etc.;
– as a pump for other sources;
– in many instruments used for industrial purposes: piercing, surface treatment, welding.
The aim of this chapter is to provide a brief review of the main sources which are available for instruments: lamps, lasers, diodes. The reader can refer to the works cited throughout the text for more in-depth information. We shall not discuss intense lasers (megajoule, Petra, etc.) which are research tools and are beyond the scope of this volume.
Light rays are emitted at the atomic and molecular levels. When the emitting medium is electrically excited, the atom or molecule is raised from its fundamental state to a higher level. Its return to the fundamental state results in the emission of a photon of energy ...