Broadband terahertz generation through intracavity nonlinear optical rectification

This paper presents a novel design for getting high signal-noise ratio broadband terahertz signal through intracavity optical rectification together with terahertz EO sampling. A nonlinear crystal as terahertz emitter is positioned inside a femtosecond laser oscillator under Brewster angle pumping configuration in order to scale up the pumping pulse power but to keep high pulse repetition rate. Our experiments show that the compact and cost-effective design improves the signal-noise ratio by about 29 times compared with the counterpart based on extracavity nonlinear optical rectification. This work opens a new way to improve the signal-noise ratio of the free-space terahertz time-domain spectroscopy through nonlinear optical rectification pumped by a femtosecond laser oscillator.