High-resolution tomographic imaging is demonstrated using a reflection-type terahertz time-domain spectroscopy. To realize a practical system for general use, a robust all-fiber laser was used as the pump light source. Broadband terahertz waves were generated with the combination of optical pulses compressed to 17 fs using optical fibers and a DAST crystal. Using deconvolution signal processing, the wideband spectrum of the generated terahertz waves provided high-axial resolution leading to successful imaging of a multilayered structure containing a 2-microm-thin GaAs layer. To our knowledge, this is the first demonstration of terahertz tomographic imaging of such a thin layer.

Nonlinear optical terahertz wave generation is a promising method for realizing a practical source with wide frequency range and high peak power. Unfortunately, many nonlinear crystals have a strong absorption in the terahertz frequency region. This limits efficient and widely tunable terahertz wave generation. The Cherenkov phase-matching method is one of the most promising techniques for overcoming these problems. We propose a prism-coupled Cherenkov phase-matching method, in which a prism with a suitable refractive index at terahertz frequencies is coupled to a nonlinear crystal. We demonstrate prism-coupled Cherenkov phase-matching terahertz generation using the DAST and LiNbO 3 crystals. With a DAST crystal, we obtain a spectral flat tunability up to 10 THz by difference frequency generation. With a LiNbO 3 crystal, we observe a spectral flat broadband terahertz pulse generation up to 5 THz pumped by a femto second fiber laser. The obtained temporal waveform is an ideal half cycle pulse suitable for reflection terahertz tomography.

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High-resolution tomographic imaging is demonstrated using a reflection-type terahertz time-domain spectroscopy. To realize a practical system for general use, a robust all-fi ber laser was used as the pump light source. Broadband terahertz waves were generated with the combination of optical pulses compressed to 17 fsec using optical fibers and an organic 4-dimethylamino-N-methyl-4-stilbazolium tosylate (DAST) crystal. Using deconvolution signal processing, the wideband spectrum of the generated terahertz waves provided high-axial resolution of 10/n μm, where n is the refractive index of sample. To our knowledge, this is the fi rst demonstration of terahertz tomographic measurement of such a high-axial resolution. Moreover, we applied this technology to dry and wet samples which structure has multilayer, and we successfully achieved the three dimensional tomographic images.