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Q: Quantenoptik

Q 16: Festkörperlaser III

Q 16.4: Vortrag

Dienstag, 17. März 1998, 14:45–15:00, P 602

Q–switching of a cladding–pumped Erbium fibrelaser at 2.7 µ m — •T. Huber, W. Lüthy, and H. P. Weber — Institut für Angewandte Physik, Universität Bern, Sidlerstrasse 5, CH-3012 Bern

Fibre lasers are easily operated in stable single transverse mode operation. They have a low threshold power and high slope efficiency. However, to couple the pump light into the core of such a fibre laser, the pump source itself has to be single or low-order mode. This limits the possible output power to typically several tens of milliwatts.

For medical applications, higher average powers in the order of 1 Watt are desirable. With the use of a double-clad fibre, high power multimode diode lasers become usable as pump source, as the pump beam only has to be focused into the inner cladding of typically 125 µ m diameter.

Further, medical applications demand pulsed operation of the laser. The idea is to use pulses that are short enough to avoid heat diffusion, but long enough to prevent mechanical damage due to shock wave generation in the tissue. An interesting pulse width for tissue processing lies in the range from 0.1 to 1 µ s. Such pulses have to be generated in a fibre of typically 10 m length, leading to a resonator round tip time of 100 ns.

Q-switching of a cladding pumped fibre laser by two different techniques – rotating mirror and acousto-optical modulator – is shown and discussed. Shortest pulse widths of 300 ns are reached.