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Efficient narrowband terahertz generation in cryogenically cooled periodically poled lithium niobate.

We present an efficiency scaling study of optical rectification in cryogenically cooled periodically poled lithium niobate for the generation of narrowband terahertz radiation using ultrashort pulses. The results show an efficiency and brilliance increase compared to previous schemes of up to 2 orders of magnitude by exploring the optimal pump pulse format at around 800 nm, and reveal saturation mechanisms limiting the conversion efficiency. We achieve >10⁻³ energy conversion efficiencies, μJ-level energies, and bandwidths <20  GHz at ∼0.5  THz, thereby showing unprecedented spectral brightness in the 0.1-1 THz range relevant to terahertz science and technology.