This chapter deals with lasers as a light source and tool, not their design, construction, or specifics. It also does not address any specific application performed with lasers as the primary light source. Both issues are supported by a wealth of literature, including an easy-to-read introduction. Therefore, the lasers are reviewed with respect to their future use and application details. Because the product group of lasers provides very different parameters, different equipment may be required to analyze their emitted light. Large variations are found in all parameters:
• the wavelength range reaches from the vacuum UV into the far-IR;
• the number of discrete emissions can be a single line, lots of lines, or so many lines that they melt together;
• the bandwidth of the signals reaches from subpicometers to several hundred nanometers;
• the signal may be steady state or pulsed (if pulsed, the pulsewidth can reach from subpicoseconds into the microsecond regime);
• the rep rate of pulsed lasers may be found to be less than 1/s, up to megahertz;
• the optical power covers microwatts through mega- or even gigawatts;
• the spectral distribution of the signals may be Gaussian, Lorentzian, or a different shape;
• the area illuminated by a laser may be tiny and circular, cover a ratherlarge circle or square, or show different dimensions in both directions (slab-shaped); and
• the homogeneity, the collimation, and the polarization of the light may be very different and change within the first millimeters after leaving the primary laser source (near field/far field).
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