Laser Fizeau Interferometer Research Articles

Coherent phase transfer function degradation due to wave aberrations of a laser Fizeau interferometer

This paper concerns a numerical technique and associated modeling results for evaluating coherent phase transfer function (CPTF) degradation that is induced by wave aberrations of the imaging train of a laser Fizeau interferometer. The CPTF is defined as the ratio of the Fourier transform of the phase portion of the complex image of a phase object formed by the interferometer to the Fourier transform of the phase object itself. A unit step function is used as the object. The aberrated image is calculated using an optical design program. The traditional instrument transfer function is the amplitude portion of the CPTF. It has been found that the phase portion of the CPTF is needed for properly characterizing the frequency response of the system when a significant amount of coma is involved. Based on the results of the study, an aberration tolerance criterion is proposed for the optical design of a laser Fizeau interferometer.

Measuring Method of Radius of Curvature Based on Dual-Frequency Laser Interferometer

In order to achieve high-accuracy measurement of radius of curvature of optical sphere, ultra-high accuracy radius of curvature testing device is developed by dual-frequency laser interferometer and Fizeau interferometer based on cat’s eye and confocal method. Through analyzing the error source models of radius of curvature testing, optical configuration of the testing device has been optimized. Precise environment control and real-time monitoring system is also established to reduce the errors caused by environment. Through the above processes, the radius of curvature measurement relative accuracy is better than 2 ppm. One optical sphere, R88.5 mm, test aperture 59 mm, has been tested. Testing result is 88499.465 ± 0.176 μm, meeting the design requirement. The method has high accuracy and practical advantages.

Axial alignment for high-precision interferometric measurements of steeply-curved spheres

Incorrect positioning of a steeply-curved sphere along the optical axis of a laser Fizeau interferometer introduces a measurement error that is proportional to the cosine of the inclination angle of the ray trace within the cavity, and directly proportional to the misalignment. The standard metrology solution is to subtract a fitted parabola from the 3D image, which corrects for most of the error, but neglects higher terms. As a consequence, measurements of steeply curved parts may have residual errors resembling spherical aberration. Here we calculate the magnitude of the error and present it in a graphical format that allows for straightforward quantification of the residual error as a function of the measured quadratic or power term in the measured 3D surface form. While our recommendation is to employ automated alignment for best results, we also consider options for higher-order software corrections for geometric misalignments.

The effect of crucible bottom deformation on the quality of Nd:GGG crystals grown by Czochralski method

AbstractIn this paper, we report the growth of neodymium doped Gadolinium Gallium Garnet (Nd: GGG) crystal using Czochralski (CZ) method, and study the effects of crucible bottom deformation and thermal insulator thickness on the growth process and crystal quality. Garnet structure and <111> crystallography orientation of the crystal were confirmed by the X‐Ray diffraction (XRD) analysis. Macroscopic defects, residual stresses, quality, and homogeneity of the crystals were investigated by means of parallel plane polariscope and laser fizeau interferometer respectively and the results compared together. Experimental observations show that the crucible bottom deformation from flat to convex, and decreasing the thickness of zirconia insulator under the crucible result in the formation of lateral cores and increasing the crystal inhomogeneity and tensions, leading to the decrease of the crystal quality. (© 2011 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

Multimode laser Fizeau interferometer for measuring the surface of a thin transparent plate

A Fizeau interferometer utilizes a multimode laser as a light source for testing thin transparent plate samples. As a result of multimode linear laser operation, interference fringes are obtained only when the optical path difference between two surfaces is equal to twice a multiple of the laser's effective cavity length. For three parallel surfaces, we can either adjust their separations or select a laser such that only two of the three surfaces meet the requirement of twice a multiple of the laser's effective cavity length.