By focusing a femtosecond laser beam onto the lateral face of a periodically poled KTP crystal, we generate a THz pulse through optical rectification of the laser pulse. The THz signal is recorded by means of a common THz time-domain technique, which allows us to obtain both the magnitude and sign of the THz waveform, and then the magnitude and phase of its spectral components thanks to a numerical Fourier-transform. By moving the laser beam along the crystal, we record a THz signal that renders for the alternative orientation of the crystal domains, with a lateral resolution as good as 10 μm, whatever the THz wavelength. This demonstrates the potential of the Optical Rectification TeraHertz Imaging (ORTI) technique to produce sub-wavelength THz images.

通过将飞秒激光束聚焦到周期性极化KTP晶体的侧面上，我们通过对激光脉冲进行光学整流来生成THz脉冲。通过常用的THz时域技术记录THz信号，借助数值傅里叶变换，我们可以同时获得THz波形的幅度和正负号，然后获得其频谱分量的幅度和相位。通过沿晶体移动激光束，我们记录了一个THz信号，该信号呈现出晶域的替代取向，无论THz波长如何，其横向分辨率都高达10μm。这证明了光学整流太赫兹成像（ORTI）技术产生亚波长THz图像的潜力。