We elucidate the effects of the lateral mode structure on the far field pattern of metal-metal
ridge-waveguide terahertz quantum cascade lasers. By introducing a 6-μ m-wide metal gap
on the top metal contact, we suppress odd-parity lateral modes and drastically modify the far
field pattern. Measurements are in good qualitative agreement with full three-dimensional
finite-difference-time-domain modeling. Experimental evidence of nonuniform current
pumping on the intensity distribution of the guided mode (and hence the far field pattern) is …