Abstract

According to the absorption properties of tissue, a laser for microsurgery should emit radiation of 2.9 µm wavelength. This wavelength is absorbed in tissue within 1 µm and leads to evaporation with a minimum thermal damage in the walls of the incision. If monomode emission is used, the laser light can be focused to a very small spot. The resulting thin coagulation layer, however, cannot stop bleeding from larger vessels. For haemostasis a wavelength of 2 µm with a penetration depth of several hundred µm is preferable. For application in surgery therefore both wavelength 2 µm and 3 µm have to be available. These wavelengths can be generated in fibre lasers doped with Erbium for 3µm emission [1] or Thulium and Holmium for 2 µm emission [2]. Monomode fibre lasers are optically excited with a pump beam that has to be launched into the small rare earth- doped core of the fibre with a diameter of typically less than 10 µm. In view of this small target also the pump laser has to be operated in low transverse mode order or even in fundamental mode. For such a pump laser the available power is limited to about 1 Watt. In our experiments an output power of 158 mW has been reached for ZBLAN:Er³⁺ fibres [1] and 30 mW for silica:Tm:Ho fibres. These values were only limited by the available pump power. The output power of CW monomode fiber lasers, can be enhanced using a double clad fibre structure [3]. Double clad fibres can be excited with powerful multimode laserdiode arrays. An output power of several Watts has already been demonstrated in a Nd³⁺ doped double clad fibre [4,5].

© 1996 IEEE