Fibers were prepared for second-harmonic generation by injecting a frequency-doubled (seed) signal with the fundamental light from a Nd:YAG laser. The relative phase shift between the seed and the second-harmonic light generated by the fiber was measured to be close to 90° (≃99 ± 9.2°). A water cell was used to sweep the relative phase of the waves with interferometric precision. Some physical consequences of a π/2 phase shift are pointed out.
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