Terahertz generation by optical rectification in lithium niobate crystal using a shadow mask

A simple approach to generate high energy, frequency and bandwidth tunable multicycle THz pulses by optical rectification (OR) of spatially shaped femtosecond laser pulses in the lithium niobate (LN) crystal is proposed and demonstrated. A one dimensional binary shadow mask is used as a laser beam shaper. By building the mask's image in the bulk LN crystal with various demagnifications, the frequency of THz generation was tuned in the range of 0.3 - 1.2 THz. There exist also an opportunity to tune the bandwidth of THz generation from 20 GHz to approximately 1 THz by changing the optical beam size on the crystal. The energy spectral density of narrowband THz generation is almost independent of the bandwidth and is typically 0.18 μJ/THz for ~1 W pump power at 1 kHz repetition rate.