The study and control of materials with extremely strong THz fields [1, 2], or the acceleration and manipulation of electrons  and protons  are emerging applications which require THz sources with unprecedented parameters. Optical rectification of femtosecond pulses with tilted pulse front in lithium niobate (LN)  has become a standard technique for efficient THz generation. Conventionally [1,5, 6], a prism-shaped LN crystal is used with a large wedge angle equal to the pulse-front tilt (63°). This results in a nonuniform pump propagation length across the beam, which lead to a spatially varying interaction length for THz generation. This negatively affects the THz beam quality and focusability, thereby limiting the achievable field strength. In order to provide uniform interaction length across large pump and THz beams, we have proposed a setup, where the nonlinear medium is a plane-parallel LN slab with an echelon structure on its input surface  (NLES, Fig. 1). Inside the LN slab, a segmented tilted pulse front is formed with an average tilt angle as required by phase matching.
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