High-resolution Wavefront Interference Detection Technology

As the driver of the Inertial Confinement Fusion (ICF), the high power solid-state laser employs a lot of large aperture optical components which must be free from periodic structures of up to 8 lines/mm, because such structures may cause small ripple amplification and lead to poor performance and system damage. Thus, accurate measurements of spatial frequencies higher than common are desired. However, typical laser. Fizeau interferometric measurements are concerned with low frequency figure errors. According to requirement of constructing our national large solid-state laser system for inertial confinement fusion, in this paper, the technique of high resolution wavefront interferometric measuring has been studied and a 100-mm-aperture high lateral resolution interferometer has been developed.Since power spectral density (PSD) is used for describing the mid-spatial frequency errors, thedefinition and the calculation method of this parameter have been analyzed. In addition, the influences ofPSD of the tilted phase step and wavefront applied window have been analyzed and corrected. Furthermore,the definition and test method of system transfer function have been presented.The interferometer is made up of illumination system, imaging system and capturing system. The models of the system transfer function (STF) in each subsystem have been constructed by calculating the propagation of phase information through interferometric system. According to these models, all kinds of factors in each subsystem that affect the STF have been analyzed in detail, such as coherence of light, the size and position of the imaging aperture, wavefront aberration of the imaging system, defocus, the parameter of CCD and so on. Based on theses conclusions, the φ100 high resolution interferometer has been designed and the tolerances of the system have been analyzed, including wavefront slope tolerances, aberration tolerances and reflectivity tolerances. Furthermore, stray lights caused by polarization beam splitter (PBS), 1/4 wave plate and the cover of CCD have been analyzed. The performance of the φ100 high resolution interferometer has been obtained, such as measurement accuracy ≤0.08λ (PV), STF≥0.65 at spatial frequency less than 2.5/mm and ratio of signal to noise (SNR) ≥4db. The comparisons between Ring of Fire? and traditional point source have been done by experiment on Sub—aperture Stitching Interferometer(SSI).