Circular involute stage.

We report the design and testing of a circular involute stage for high-repetition-rate (hundreds of hertz), fine temporal resolution (better than 10 fs), and long delay range (as great as nanoseconds) time-resolved optical experiments. This stage uses a reflector with the involute profile of a circle as well as a pair of optical mirrors mounted upon a rotating plate to guide the optical beam, following the tangent of the circle. This circular involute stage provides unprecedented performance for optical interference, high-resolution terahertz time-domain spectroscopy, and general optical pump-probe experiments.