The multiple beam interference of the laser reflectance is a conventional method used to monitor the growth of thin films. In this paper we present the application of this method for the fabrication of diamond X-ray windows. The growth process and optical properties were studied in real time by in-situ reflectivity measurement and curve fitting. The research results are in good agreement with the measurement results of the SEM

XRD and α-step surface outline. Using the research results

we fabricate a type of Φ4-8 mm backing-free X-ray windows with high transmission successfully. The transmission was measured at Beijing Synchrotron Radiation Facility (BSRF)of the Chinese Academy of Sciences. The samples remained undamaged after the transmission measurement

therefore

the windows showed the distinct advantages of low absorption and strong radiation resistance.