  General physical conditions for the occurrence of photonic Klein tunneling
are studied, where (controlled) spontaneous emission from the devices
considered plays a key role. The specific example of a simple dielectric slab
bounded by two dielectric half spaces with arbitrary refractive indices is
worked out quite in detail, the measured reflection and transmission
probabilities being calculated analytically. It is found that, in given cases,
the measured reflection probability may be arbitrarily large (for large
incident wavelengths) irrespective of the fact that the transmission
probability is exponentially suppressed or not. Other interesting features of
photonic Klein tunneling driven by (controlled) spontaneous emission are as
well envisaged for practical applications.
