Fiber lasers

A fiber laser is a specific form of the solid-state laser. The doped core of a glass fiber is the active medium of the fiber laser. It is therefore a glass laser with optical fiber properties. The laser radiation, which is routed through the laser-active fiber, is objected due to the length to a very high amplification.
Fiber lasers are normally optically pumped by the incorporation of the radiation in its shell, parallel to the fiber core. The most common doping element for the laser-active fiber core is erbium, followed by ytterbium and neodym.
Fiber lasers possess unique properties, e.g. an electrical-optical efficiency of up to more than 30%, superior radiation quality, long lifetime and a compact, maintenance-free and insensitive construction.
A fiber laser consists of one or more pump laser diodes, optical probe and resonator.
After leaving the active fiver, the laser beam is normally transferred in an optical glass fiber or in optical cable glass fibers, which route the radiation for example to the focusing optics of a laser treatment machine.
Fiber laser machines further include the power supply and the cooling for the pump laser diodes.
Strong fiber lasers possess a small fiber laser or a strong FBG laser diode as seed laser for the generation of the input power for a following fiber laser (optically pumped active laser). The separation of the laser into seed laser and post-amplification is advantageous, because it facilitates the control of the laser actions. This concerns the wave length stability, the beam quality and the power stability resp. the pulsability.

Nd:YAG-Lasers

Nd:YAG-lasers (short for neodymium-doped yttrium-aluminum-garnet-laser) are solid-state-lasers, which use a neodymium doped YAG crystal as active medium and emit infrared radiation with a wavelength of 1064 nm. An advantage over the often used CO2 lasers is the possibility of routing the laser beam in very fine bundles, due to its small wavelength. With this laser, high medium powers (up to 10 kW in serial lasers) can be achieved. The laser can be operated both in continuous (CW, continuous wave) and pulsed mode.
Pulsed mode is achieved by pulsed pumping (flashlights), Q-switching or mode coupling. When Q-switching is used, peak powers of several hundreds of megawatts can be reached.
The efficiency of lamp-pumped systems is around 3 to 5 percent, because only a small part of the radiation spectrum will be within the pump level. For example, a laser with 3 kW optical power requires ca. 60 kW input power, and 57 kW have to be removed as heat. The activation of the neodymium ions is normally achieved by gas discharge lamps (flash or arc lamps containing xenon or krypton).

The mean lifetime of the activated electrons of the neodymium ions is around 230 µs. Due to this relatively long span it is possible to store energy in the crystal, which can subsequently be used in a short pulse (10 … 100 ns, „Q-switch“).