The development of synchrotron radiation (SR) technology has made a qualitative breakthrough in the luminance of M?ssburger sources. However, the traditional method based on the silicon lattice constant is still adopted in the experiment of wavelength measurement, and the measurement accuracy is affected by the uncertainty of the silicon lattice (2×10-8). Since Bonse and Hart published their experimental results in 1965, the X-ray interferometer has been widely used for precision measurement of parameters, such as lattice constants, due to its extremely high accuracy. This interferometer technology can be used for accurate measurement of silicon lattice constants independent of X-ray wavelength values. The first report on the X-ray Michelson interferometer came from Appel and Bonse in 1991, who added a group of single channel-cut diffraction devices with adjustable optical paths into the space of the Laue-Laue-Laue (LLL) interferometer to form the structure of the interferometer. However, the Michelson interferometer based on this structure is not suitable for measuring the M?ssburger resonance wavelength at which its operating wavelength is not around 14.4 keV, and the adjustable range is limited (a few micrometers) as the optical path difference in the interferometer is formed by the rotation of the optical components, which can hardly achieve high-precision measurement. We design an X-ray Michelson interferometer, which can be used to measure 14.4 keV M?ssburger resonance wavelength. The LLL-interferometer and the monolithic double channel-cut monochromator (MDCM) that can accurately measure the optical path difference are fabricated. The key parameters such as the fringe contrast of the LLL-interferometer, diffraction bandwidth of MDCM, and relative displacement of the exit-beam position are measured online, which provides a technical basis and device foundation for the subsequent integration test of the Michelson interferometer.
The new design of the X-ray Michelson interferometer is shown in Fig. 1. The non-dispersive LLL-interferometer can be transformed into a dispersive Michelson interferometer when an MDCM that can pass through 14.4 keV photons is inserted into the space of the monolithic LLL-interferometer. The specially designed MDCM has two optical paths, upper and lower, each consisting of four Bragg reflections in two grooves. With the crystal plane combination with an appropriate index selected from monocrystalline silicon and ingenious structure design, 14.4 keV photons incident at the Bragg angle can pass through MDCM exactly after four consecutive reflections and keep the original direction of propagation. The application of certain pressure on the upper surface of the crystal can change the upper channel-cut width, which introduces an adjustable optical path difference between the upper and lower paths. At the same time, the optical path difference is accurately measured by the visible light interferometer, and X-ray wavelength measurement independent of lattice constants can be achieved by the comparison of the interference fringe orders between visible light and X-ray.
This paper introduces a new X-ray Michelson interferometer design that can be used for ultra-precise measurement of 57Fe 14.4 keV M?ssburger nuclear resonance wavelength. The new design consists of a monolithic anti-symmetrical LLL-interferometer and an MDCM, which can match the X-ray with a wavelength of 14.4 keV. The performance of the first homemade LLL-interferometer in China and the working conditions of MDCM are measured online and characterized quantificationally by a 14.4 keV monochromatic X-ray at SSRF. The measurement results of the fringe visibility (0.37-0.63) of the LLL-interferometer and correction parameters of MDCM are obtained, which provide experience and a technical basis for the development and online characterization of X-ray optical elements with complex configurations in China.