Analysis Of White-light Interferograms Research Articles

Film Thickness Analysis for EHL Contacts under Steady‐State and Transient Conditions by Automatic Digital Image Processing

The knowledge of the film thickness values is very important in lubricated contacts to verify the lubrication conditions. Optical interferometry is one of the most used methodologies for film thickness and shape determination of Elastohydrodynamic‐lubricated contacts. An image processing programme has been developed for the analysis of white light interferograms. The programme, based on the analysis of the hue channel, has been developed in order to process big amounts of images, as often generated under transient conditions. The measurement range is currently limited to a maximum film thickness of 0.7 μm. The programme has been used for analysing several images recorded in tests carried out with a ball on disc contact under steady‐state as well as transient conditions for different velocities and slide‐to‐roll ratios. Under transient conditions, the entraining velocity is varied with a sinusoidal law for two different frequencies. The results obtained evidenced an asymmetric reduction of the film thickness when increasing the percentage of sliding, both for stationary and transient conditions. Under transient conditions with increasing test frequency, film thickness loops of increasing amplitude have been found that reduce their amplitude more when the ball is running faster than the disc. Squeeze and thermal effects can explain the results obtained.

High resolution group refractive index measurement by broadband supercontinuum interferometry and wavelet-transform analysis

In this paper we propose group refractive index measurement with a spectral interferometric set-up using a broadband supercontinuum generated in an air-silica Microstructured Optical Fibre (MOF) pumped with a picosecond pulsed microchip laser. This source authorizes high fringes visibility for dispersion measurements by Spectroscopic Analysis of White Light Interferograms (SAWLI). Phase calculation is assumed by a wavelet transform procedure combined with a curve fit of the recorded channelled spectrum intensity. This approach provides high resolution and absolute group refractive index measurements along one line of the sample by recording a single 2D spectral interferogram without mechanical scanning.

Analysis of white light interferograms using wavelet methods

Several methods for the analysis of white light interferograms are presented and their performance is compared to a new method employing the wavelet transform in connection with sub-Nyquist sampling. As the result of computer simulations and experiments the wavelet method proves to be best suited to the problem.

High-resolution profilometry by using phase calculation algorithms for spectroscopic analysis of white-light interferograms

High-resolution profilometry by using phase calculation algorithms for spectroscopic analysis of white-light interferograms

Surface Profiling by Analysis of White-light Interferograms in the Spatial Frequency Domain

Abstract We describe a scanning white-light interferometer for high-precision surface structure analysis. Interferograms for each of the image points in the field of view of the instrument are generated simultaneously by scanning the object in a direction perpendicular to the object surface, while recording detector data in digital memory. These interferograms are then transformed into the spatial frequency domain and the surface height for each point is obtained by examination of the complex phase as a function of frequency. The final step is the creation of a complete three-dimensional image constructed from the height data and corresponding image plane coordinates. The measurement repeatability is better than 0·5 nm r.m.s. for a surface height range of 100 μm.