Two-color interferometry using a detuned frequency-doubling crystal

Phase mismatch by angular detuning permits continuous variation of the intensity of second-harmonic light generated in a nonlinear crystal while maintaining a controlled phase relationship between the first and second harmonics. Interference of this second-harmonic light with second-harmonic light generated in a second crystal was measured and can be understood by taking beam walk-off into account. When the second crystal is replaced by a fiber, the phase of the χ(2) grating in the fiber is measured to be 88 ± 4°, which differs by 180° from recently reported results.