Fourier optical phenomena and applications using ultra broadband terahertz waves

Abstract

Pulsed terahertz (THz) waves which are generated from femtosecond laser pulses have ultra-broad bandwidth compared to other frequency electromagnetic waves. In addition, phase measurement of pulsed THz waves is very convenient because we can directly measure the field of them. In this dissertation, we study Fourier optical phenomena and their applications with these ultra broadband pulsed THz waves.

Diffraction pattern can be achieved by spectral analysis of ultra broadband THz waves instead of scan detection. With this principle, we demonstrate three different single-pixel diffraction imaging systems which need only one dimensional data acquisition processes for two dimensional imaging. In the first experiment, we set a coherent optical computer and show that complex 2D images are reconstructed with only 30 waveform measurements by rotating a hole mask placed in the spatial frequency domain. In the second, we also demonstrate one waveform diffraction imaging with the time separating hole mask in the coherent optical computer. In the last experiment, we use a wedge prism, or a slanted phase retarder, instead of the coherent optical computer and achieve much higher signal-to-noise-rate imaging.

Polarization of ultra broadband THz waves is not easily represented by polarization theories of monochromatic waves. To show this, we shape unconventional polarization states of few-cycle THz pulse by illuminating spatiotemporal controlled ultrafast laser pulses on a circularly metal-patterned InAs thin film surface. For this polarization shaping, a set of wedges having various directions and thicknesses are arranged to achieve proper spatiotemporal controlling of ultrafast laser pulses. By them, we generate THz waves of various uncommon polarization states, such as polarization alternation between right and left circular polarization states. We also define a time domain representation of polarization to analyze these types of polarization.

We also study sub-w...