DPW - ease of use
Fourier-transform infrared surface science experiments require the use of high intensity, closely controlled infrared (IR) light. Since most IR light sources are not UHV compatible, a sealed viewport must be used to admit the light. Conventional viewport materials, such as pyrex and quartz can be readily sealed by vacuum brazing but do not usually admit the light frequencies required. Materials that DO transmit IR well are often costly, very soft and will become cloudy from moisture in the laboratory atmosphere.
The MTS' Differentially Pumped Window Flange (DPW) is used to mount special metal-halide windows to the ultra-high vacuum system that can not be sealed by conventional means. The flanges are available in a wide range of sizes to accept commercially available windows. The user can easily remove the aluminum retainer, polish and replace windows that have become cloudy, thereby extending useful life. Also, if the experimental requirements change, only the window itself need be changed, at considerable cost savings.
Under normal conditions your DPW will provide years of trouble-free service, especially if simple maintenance is performed. By pumping on the differential section with only a mechanical pump, UHV pressures on the inside can be routinely achieved. Note that the "O" ring seals on both sides of the window (in the cover plate as well as in the flange) protrude a little to prevent the metal surfaces from actually contacting the fragile window material. Should you discover a situation to the contrary, stop and double check. It may be time to replace the seals.
IR beams can be dispersed when passing through air, due to ambient moisture. An optional extension retainer is available for attaching a N2 purged volume. Contact the factory for dimensions and details.
For example, the DPW275 is designed to accept the user's standard, 38 mm OD X 6 mm thick window and other sizes are listed below. No window is supplied. Because of the wide variety of window materials available, the choice of material is best left up to the user. See the drawing.
When replacing the cover, it is best to tighten the screws evenly. This prevents binding and possible damage to the window. It also results in a more uniform seal. Two sets (one spare) of seals are provided. The fluorocarbon seal material can be baked to 150°C. Store the spare seal set in a clean place to prevent damage or contamination.