Actively controlled enhancement cavity for terahertz generation

We report on the efficient Cherenkov-type terahertz (THz) generation using lithium niobate crystals and a high repetition rate femtosecond laser. An actively length controlled synchronously pumped ring resonator acts as an enhancement cavity for the near infrared pump and therefore recycles the available pump power towards a higher terahertz output. A seven times higher THz field amplitude was measured with electro-optical sampling.