Optical resonators are widely used for power enhancement, high harmonic generation and sensitive absorption spectroscopy [1-4]. The usual way of filling a laser resonator with light is to couple in through a slightly transparent mirror. We demonstrate an alternative method by using a pellicle located in the cavity at an angle of incidence close to the Brewster angle. By adjusting the angle of the pellicle the amount of input coupling can be varied and thus the cavity can be operated at different values of finesse without changing components. A further advantage is the low dispersion induced by the input coupler, allowing a broad frequency comb to be resonant.
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