Relative spectral response measurement of spectrometers using undulator radiation

Abstract

Undulator radiation with known spectral characteristics is recognized as an excellent light source that can be used to measure the spectral response of a variety of spectral measurement devices in a wide range from infrared to x-ray. This technique has been developed at Duke Free-Electron Laser (FEL) Laboratory to successfully measure the spectral response of several spectrometers in the near-infrared, visible, and ultraviolet regions. In this paper, we present both simulation and experimental results of the spectral response measurement, with a focus on high-accuracy spectral response reconstruction. Using simulation studies, we have tested and confirmed the validity of the spectral response measurement method while taking into account major sources of errors. Especially, it shows that the spectral response reconstruction technique developed in this work is rather robust against the spectral broadening of undulator radiation. The usefulness of this spectral response measurement method is also confirmed with the experimental study on a spectrometer in the visible region. Overall, we have achieved good results with the measured spectral response, with an RMS uncertainty of about 2.7% in the range from 414 to 591 nm. Using multiple measurements, the reproducibility of this method has also been tested with a relative difference of about 2.3% (RMS in the range from 415 to 590 nm). For high-accuracy measurements of a broad radiation spectrum, the knowledge of the spectral response of the spectrometer is critical. In this paper, we will show that the details of the measured undulator radiation spectra can be properly restored by correcting the raw spectrum using the measured spectral response. The method of spectral response measurement using undulator radiation is also useful to calibrate spectral devices in extreme spectral ranges such as VUV and x-ray.