  A Schottky diode integrated into a terahertz quantum cascade laser waveguide
couples directly to the internal laser fields. In a multimode laser, the diode
response is correlated with both the instantaneous power and the coupling
strength to the diode of each lasing mode. Measurements of the rectified
response of diodes integrated in two quantum cascade laser cavities at
different locations indicate that the relative diode position strongly
influences the laser-diode coupling.
