Time reversal terahertz imaging

We describe a technique for imaging in the terahertz regime using time reversal of single-cycle pulses. Specifically, the time-reversal symmetry of Maxwell´s wave equation is exploited to reconstruct the transmission function of a diffracting aperture by inverting the diffracted fields. After deriving a time-reversed form of the Huygens-Fresnel diffraction integral, we demonstrate through simulation and experiment the reconstruction of one-dimensional and two-dimensional (2-D) objects. A means to obtain data efficiently for reconstruction of 2-D apertures is described. The spatial resolution determined by the Sparrow criterion is found to correspond to approximately 30% of the peak wavelength and 85% of the mean wavelength of the power spectrum of the single-cycle waveform. Finally, the modulation transfer function for the imaging method is simulated and is shown to be nearly diffraction-limited when compared to an ideal imaging system.