The risk and injury of the eye in the form of coagulative damage to the retina from lasers exists even at powers of less than one milliwatt due to the focusing of the beam on the retina. At wavelengths greater than 1.4 microns, however, this risk is significantly lower than at shorter wavelengths since the radiation is no longer optimally focused by the eye lens, thus reducing the radiation intensity on the retina.
For this reason, these longer wavelength lasers enable applications such as LIDAR measurements for atmospheric research or remote detection with a significantly reduced risk potential. Significantly lower requirements may also be imposed for the screening of scattered radiation from activities such as materials processing when using such lasers.
At the Institute of Technical Physics, an Ho:YAG thin disk lasers with an emission wavelength of two microns have already been realised as an efficient and scalable source with the potential to generate high pulse energies.
Compound semiconductors doped with transition metals, in particular Cr:ZnSe, provide a wide range of amplification in the two to three micron range and are very suitable as the laser medium for remote detection systems which are based on the measurement of molecular vibrational and rotational transitions.