Phase-shifting point diffraction interferometer

Abstract

We describe a novel interferometer design suitable for highly accurate measurement of wave-front aberrations over a wide range of wavelengths, from visible to x ray. The new design, based on the point diffraction interferometer, preserves the advantages of the conventional point diffraction interferometer but offers higher efficiency and improved accuracy through phase shifting. These qualities make it applicable to at-wavelength testing of many optical systems, including short-wavelength projection lithography optics. A visible-light prototype was built and operated.

Recent developments in X-UV optics and X-UV diagnostics

“…From the first experiments of Da Silva and collaborators [3] or Joyeux et al [4], many interferometers have been set up (Mach-Zehnder [3], Fresnel bimirror [4], Lloyds [5], SMARTT [6], etc.). At LIXAM/LCFIO, we have chosen to develop the so-called Michelson interferometer [7] (Fig.…”

Phase-Shifting Point Diffraction Interferometer Having Two Point Light Sources of Single-Mode Optical Fibers

“…14 shows a flow chart of the measurement. (Smartt & Steel, 1975;Sommargren, 1996;Medecki et al, 1996;Millerd et al, 2004;Otaki et al, 2002b). In contrast, the PS/PDI described in this chapter uses two optical fibers as light sources, and the interferogram generated by these two fibers is recorded by a CCD camera.…”

“…The precursor to the PDI was an interferometer with an optical diffraction wave emitted from a tiny aperture fabricated on a so-called PDI plate, and the diffraction wave was used as a reference spherical wave for interferometry (Smartt & Steel, 1975;Sommargren, 1996;Medecki et al, 1996;Millerd et al, 2004;Otaki et al, 2002b;Ota et al, 2001). Presently, demand is growing for highly precise optical surfaces, both spherical and aspherical, in the case of mirrors.…”

“…Production of high-precision mirrors with large surface areas is usually supported by highly accurate surface figure measurement methods. For example, the slope integration method (Higashi et al, 2007), three-flat method (Schulz & Schwider, 1967), and point diffraction interferometry (PDI) (Smartt & Steel, 1975;Sommargren, 1996;Medecki et al, 1996;Millerd et al, 2004;Otaki et al, 2002b) have been studied and applied to the measurement of mirrors. The slope integration method determines the surface normal vector at each point on the test surface and the resultant angle of inclination is integrated to obtain the absolute surface figure.…”

At-wavelength interferometry of extreme ultraviolet lithographic optics

“…The PS/PDI is briefly explained here; a more complete description can be found in the literature (3,5). The PS/PDI is a modified version of the conventional point diffraction interferometer with improved efficiency and phase-shifting capability.…”