A laser device includes a solid state laser element consisting of a yttrium aluminate crystal and a source of pumping light. A light filter which intercepts and removes pumping light components having wave-lengths below about 5,000A is disposed between the laser element and the light source. The removal of these selected higher frequency components lowers the oscillation threshold value and increases the laser output.

Iron is close to a major surface layer of a yttrium aluminate laser rod so that the layer portion may have a filtering effect. The absorption factor for the short wavelength light of this layer portion depends upon the concentration c (weight percent) of the contained iron and the thickness t (.mu.m) of the iron-containing layer. Consequently, the effect of the iron in the laser rod can be evaluated as a function of the product c.times.t (wt%..mu.m) of the concentration c and the thickness t. In the range of the product c.times.t of 1<c.t<2.times.10.sup.2, a laser output could be obtained which is higher than that of the conventional laser rod not containing iron jointly with a short wavelength light filter. The thickness of the iron-containing layer is 1/4 or less of the radius of the laser rod.

A coupled ion laser operating at a frequency determined by the energy levels characteristic of the coupling of a lanthanide or actinide group ion with an iron group ion in an orthoaluminate material, such as yttrium orthoaluminate, is described in which low threshold high efficiency starting operation at predetermined frequencies in the region of eye safety is provided.

The invention is directed to an ophthalmologic apparatus which includes a laser module which permits microsurgery with pulsed radiation as well as coagulation therapy by means of continuous-wave radiation.

Co-doping the gain medium of a diode-pumped infrared laser to make the laser resistant to long-term degradation from high-intensity internal infrared radiation is disclosed. Co-doping the gain medium with ions such as Cr.sup.3+ and Ce.sup.3+ that make the gain medium resistant to external ionizing radiation solves problems of long-term degradation of the gain medium.