Method for evaluation of high-order and scattered light in outgoing beam from grazing incidence grating spectrograph

Various types of grazing incidence grating spectrograph systems are available to provide monochromatic light in the vacuum ultraviolet ray and soft X-ray region. In general, these spectrographs are compared and evaluated in terms of outgoing light intensity, resolution and spectral purity. The report describes a method to evaluate the scattered and high-order light in the outgoing beam from a grazing incidence grating spectrograph. This method is based on the energy resolving power of a proportional counter filled with hydrocarbon molecules, and the relatively high permeability of a thin film window. In general, a filter is used to increase the spectrum purity in this wavelength region. The proposed method provides a tool for easy, accurate evaluation of the effects of the filter. Some instruments are describe which can extract the first-order light component from the pulse height distribution. The use of the first-order light permits accurate determination of the permeability and reflectance regardless of the purity of the incident light. (N.K.)