Contact Rainbow Optics for all your custom optical needs. They offer Multiple-Order Quartz Waveplates, Zero-Order Quartz Waveplates and Optical Beam Isolators to name a few.  For more information, Rainbow Optics provides a graph and specifications online for more precise ordering. Rainbow Research Optics offers many optical services with excellent customer care throughout the project.  To view their optical filter graphs, visit www.rainbowoptics.com today!