A light energy delivery head is provided which, in one aspect, mounts
laser diode bars or other light energy emitters in a heat sink block
which is adapted to cool both the emitters and a surface of a medium with
which the head is in contact and to which it is applying light energy. In
another aspect, various retroreflection configurations are provided which
optimize retroreflection of back-scattered light energy from the medium.
The size of the aperture through which light energy is applied to the
medium is also controlled so as to provide a desired amplification
coefficient as a result of retroreflection.