RaySpec SDD – Window Material and Thickness

Detector Window Transmission

Entrance windows are used to protect the SDD sensor and maintain it in a controlled environment.  In the soft X-ray region, up to about 2keV, the choice of window will significantly affect the transmission. For energies below 1keV, polymer windows (Moxtek AP3.3) provide improved low energy sensitivity compared to the thicker and more robust Beryllium windows.

However, at energies over 1.4keV the support grid required by the polymer film limits transmission and Beryllium becomes the better option (see chart below)

Polymer windows have traditionally been the material of choice for low energy applications.  More recently, Silicon Nitride (Si₃N₄₎ windows have become available which offer a very useful alternative.  The low energy transmission curves of two polymer (Moxtek AP3.3 and AP3.7) windows and a typical Si₃N₄ window are shown in the chart below.

Sensor area is a factor which influences the window choice.  As larger areas are required, the window must be thicker in order to support the differential pressure.

For the ultimate low energy performance, RaySpec can customise detectors with windowless sensors and incorporate gate valves and bellows as required into the design.