Capturing a light pulse in a short high-finesse cavity

We describe a method to couple a light pulse into a cavity with arbitrarily high finesse, with an efficiency that in theory can approach 100% even if the pulse duration is much longer than the round-trip time of the cavity. The spectrum of the pulse is compressed into a single narrow mode in an adiabatic and reversible way. The method uses an input coupler with a variable effective reflectivity which is adapted to match the known temporal shape of the pulse. In addition to a theoretical description of the method, we demonstrate the principle experimentally.