Interferometric measurement of femtosecond wave-packet tilting in rutile crystal

We measured the tilting of a femtosecond laser wave packet in a birefringent rutile crystal. The measurements were carried out with a linear interferometric technique that, in contrast to nonlinear correlation techniques, allows measurement at very low power. A 23-fs delay between the left and the right parts of a 30-fs, 800-nm wave packet with 20° divergence was measured for a 1-mm-thick rutile crystal, in agreement with theoretical predictions.