Application of point diffraction interferometry for middle spatial frequency roughness detection

Abstract

The possibilities of applying the point diffraction interferometry (PDI) method for the detection of the middle spatial frequency roughness of superpolished optical surfaces are analyzed. The point source used in the experiment is based on a single mode optical fiber with the subwavelength exit aperture size, which is about 0.25 μm. In a numerical aperture of 0.01 the reference wave root-mean-square deformation is less than 0.005 nm. It is theoretically shown that the possible diffraction-limited lateral resolution of PDI while measuring a spherical substrate of 100 mm curvature radius is about 8 μm. The experiment demonstrated the possibility of obtaining roughness spectra in the range 0.001-0.05 μm(-1). The surface map obtained by PDI, and the roughness spectra obtained by both the PDI and atomic-force microscopy methods are shown.

Получение Гладких Высокоточных Поверхностей Методом Механического Притира

“…Плоские образцы могут измеряться с помощью диффузного рассеяния рентгеновского излучения (ДРРИ) [27,28], которое при определенных условиях [29] можно отнести к " первопринципному" методу. Следует отметить еще один метод измерения среднечастотных шероховатостей, использующий интерферометрию с дифракционной волной сравнения, который так же можно отнести к " первопринципному", но который пока не нашел широкого распространения [30]. Для измерения высокочастотных шероховатостей применяются атомносиловые микроскопы (АСМ) [31].…”

Geometrical aberration measurement by experimental ray-tracing based on fiber point diffraction interferometry

“…Fringe deflectometry reconstructs the transmitted wavefront through the fringes produced by the grating or screen, and its accuracy is restricted by the grating quality and the nonlinear response of the charge-couple device (CCD) and screen. PDI uses the approximate ideal spherical wavefront emitted from a fiber or pinhole as the reference wavefront and has been applied to absolute three-dimensional coordinate, distance [10][11][12], surface shape [13,14], and wavefront measurement [15,16]. Although the measurement accuracy can achieve the sub-nanometer level, it is still affected by the poor diffraction light power of the pinhole or diffraction wavefront with the low numerical aperture of the fiber.…”

Computer-aided high-accuracy testing of reflective surface with reverse Hartmann test

“…The interferometers, such as Fizeau interferometer, TwymanGreen interferometer and point-diffraction interferometer [1][2][3][4][5], have been widely applied as a powerful noncontact testing method. The accuracy of interferometric method can reach the order of nanometers and even subnanometers, however, its dynamic range is quite small [6].…”