| 摘要 |
A method and apparatus for frequency shifting an optical beam where the frequency shifted beam remains both spatially and temporally coherent with no spread in frequency and can be continually tuned in frequency shift over a wide range without any change in beam pointing or beam quality with time. This is achieved by changing the effective optical path length of the resonant cavity of a laser by translating an optical wedge, such as a prism, across the optical path in the direction of the wedge gradient. In a first embodiment, a rotating helical phase plate is used to linearly increase the optical path of a transmitted or reflected beam with time, thereby frequency shifting the exiting beam. In another embodiment, the rim of a wheel with a spirally increasing or decreasing radius is used in which the outer periphery of the wheel is a mirror. Spinning the wheel at a constant rotational speed increases or decreases the optical path of a reflected beam linearly with time, thereby frequency shifting the reflected beam. The helical phase plate can be used in either a transmissive mode or a reflective mode, whereas the spiral wheel is used primarily in a reflective mode.
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