Abstract: A device for the ablation of biological substances by laser radiation, especially for stomatologic treatment, comprises a pump laser and a laser converter for converting the pump laser radiation into a laser radiation having the wavelength range of 3 &mgr;m±0.2 &mgr;m, wherein the laser converter is accommodated in a treatment head which is separated from the pump laser by a fiber-optic device. There is provided in the laser converter a metal-holmium-fluoride crystal with an alkaline or alkaline-earth ion as metal ion with partial substitution of the holmium (Ho) ions, namely one of the following compounds: Me(Ho1-xPrx)F4 with a metal ion of lithium (Li) or sodium (Na), a fluorine ion, and with components of praseodymium of x=0.001 to 0.03, or Ba(Ho1-xPrx)2F8, where Ba is a barium ion, F is a fluorine ion, and with components of praseodymium of x=0.0005 to 0.015.