A semiconductor laser comprises an active region (12) which, in response
to a pumping energy applied thereto, can produce a stimulated emission of
radiation with a central wavelength (.lamda.) in the far infrared region,
and a confinement region (16, 18, 22) suitable for confining the
radiation in the active region (12), and comprising at least one
interface (16a, 16b, 22a) between adjacent layers that is capable of
supporting surface plasmon modes generated by an interaction of the
interface with the radiation. The confinement region (16, 18, 22)
comprises a wave-guide layer (16) which is delimited on opposite sides by
a first interface and by a second interface (16a, 16b). The guide layer
(16) is doped in a manner such that the first and second interfaces (16a,
16b) are capable of supporting the plasmon modes, respectively, and is of
a thickness (d) such as to bring about the accumulation of the plasmon
modes in proximity to the first and second interfaces (16a, 16b), outside
the layer (16), and substantially a suppression of the plasmon modes,
inside the layer.