Arbitrary terahertz pulse shaping via optical rectification in fanned-out periodically-poled lithium niobate

We demonstrate a novel terahertz (THz) pulse shaping technique, which guarantees ultimate flexibility for arbitrary THz pulse generation. The THz pulse shaper consists of a fanned-out periodically-poled lithium niobate (FO-PPLN) crystal-the domain width of the FO-PPLN crystal varies continuously across the lateral direction-, a spatial mask, and a spherical mirror. Optical pulses are line-focused on the FO-PPLN crystal to generate spatially separated multi-frequency components of THz pulses. The spatial mask is placed in front of the FO-PPLN crystal in order to manipulate the spatial pattern of the incident optical beam, thus to control the amplitudes of the spatially dispersed THz frequency components. Spectral resolution of this method is determined by FO-PPLN bandwidth and mask resolution: estimated practical resolution is 0.01 THz for 1 THz bandwidth. After the spherical mirror assembles the various frequencies into a single collimated beam, a shaped THz pulse can be obtained, with the pulse shape determined by the Fourier transform of the pattern transferred by the mask. As a proof-of-principle experiment, we measured THz waveforms using metal masks. The experiment was performed using 800-nm, 100-fs pulses from a 1-kHz Ti:sapphire regenerative amplifier. We used a 5-mm long FO-PPLN sample (width = 10 mm, height = 0.5 mm) continuously tunable from 0.6 to 1.5 THz. We tested the metal masks of three different spatial patterns: low-pass filter, high-pass filter, and double slit. The experimental results show that the THz waveforms are determined by the spatial patterns of the masks.