Tower’s 17.5mm Zero order waveplates provide users with a high performance Crystal Quartz retarder with a clear aperture of 15mm. These waveplates are air spaced, having a stainless steel spacer between two crystal quartz plates that form the zero order capability. Zero order waveplates are far less sensitive to temperature variations than multi-order waveplates. Air spaced waveplates have higher thermal stability and power handling capability than contacted or cemented waveplates. There are no failures as occur with contacted waveplates coming apart. Angular alignment of the waveplates is also more accurate. Tower Optical waveplates are made from Laser quality Crystal Quartz. Each plate is AR coated on both sides. Standard retardations are ½ or ¼ wave. These waveplates are offered either unmounted with a diameter of 17.5mm or mounted in a 25.4mm anodized Aluminum mounting ring with a 15mm clear aperture. The standard wavelengths available are shown in the chart below. As a special feature, Tower offers the ability to supply these zero order waveplates at wavelengths within a range of 10–20nm from any of those listed on the chart. Other wavelengths are available on a custom order basis.