Demonstration of terahertz frequency-dependent field transformation in an irregular waveguide structure with direct measurement of the internal electric fields.

We demonstrate irregular scattering structure frequency-dependent field control at terahertz frequencies by means of a TM(10) to TM(30) mode converter designed for operation near 300 GHz and fabricated out of lithium niobate. Imaging of the electric fields in the sample, with a Fourier analysis of the time domain signal, yielded the performance as a function of frequency.