Cleveland Crystals Inc. has launched the XTP line of large-aperture, very thin KDP/KD*P wave plates and mounts for use with ultrashort-pulse lasers for harmonic generation and difference frequency mixing. The crystals' thinness minimizes the effects of group-velocity mismatch and dispersion in femtosecond lasers, and their large beam diameters reduce the risk of laser damage caused by excessive intensity. Aspect ratios are as large as 200:1, with low wavefront distortion. The wave plates have apertures as large as 420 mm2, resulting in a transmitted wavefront error of λ/5 or better, at 633 nm. The harmonic generators and the wave plates are available with antireflection coatings.