The research at FOI concerning protection against laser has until now mainly been focused on protection of eyes against damaging and distracting radiation. Military optical sensors active in the range 3 - 5 µm can also be subject to damage or distraction by laser. The development of anti-sensor lasers for use on IR sensitive target designators has been intense in recent years. The achievements in area protection of target designator devices from laser are still in their cradles. The requirements set on IR protection are slightly different from those set on lasers of visual wavelengths, and other physical principles can also be used. Examples are 1) Mott-transitions e.g. VO2, 2) excitation of charged carriers in semiconductors (InAs), and 3) polarization twist in LC components. In this report these three principles are exemplified by elementary laser damage threshold studies.