FTXR –
X-ray Fourier Transform Spectroscopy

Dreamer: Chuzida Chen, Andrew Lindburg

Fourier transform spectrometers (FTS) are widely used in the visible and infrared regimes, where they offer high resolution, broadband operation, high light efficiency, and compact form factors. They are also employed at synchrotron light sources for specialized techniques such as nano-FTIR. However, their development in the soft X-ray regime has been significantly slower due to three fundamental technical challenges.

First, suitable beamsplitters are lacking. Most beamsplitters operate in transmission, but the absorption length in the soft X-ray regime is on the order of micrometers, rendering this approach impractical. Second, the required optical quality is extremely stringent, with tolerances often at the nanometer scale. Third, maintaining the mechanical stability of the scanning mechanism to within a fraction of the operational wavelength demands exceptionally precise feedback systems and a tightly controlled environment.

To address these challenges, we are developing several FTS designs and building visible-light prototypes to elucidate the implementation details and technical challenges relevant to soft X-ray measurements.

Selected dream work:

• Theoretical framework for soft X-ray Fourier transform spectroscopy using the Wigner function (2026)

• A review and analysis of Fourier transform spectroscopy in the soft X-ray region: advancing historical designs with modern technology (2025)

Resources:

• Github repository (private): https://github.com/dream-beam/ftxr