MESO, an interferometer-like setup working with incoherent light for thin plane-parallel optics testing

Optical substrates with parallel surfaces are widely used in todays photonics devices. Whether they have flat (screens, filters, beamsplitters, crystals) or spherical (such as optical domes) surfaces, the metrology of such objects is complicated as they can cause unwanted interference which compromise the precision of the optical metrology performed. We have developed a new instrument whose optical path is similar to that of Fizeau-type interferometers, but which uses a light source with low temporal coherence. This implementation brings to main advantages: it avoids the generation of interference generated by the back surface of the thin-plane parallel optics to be tested; it provides a significant degree of freedom when it comes to choosing a wavelength of test. This makes it possible to characterize optical components independently of their thickness, spectral transmission and coatings. In this communication, we will detail the method developed and compare it with other wavefront sensing solutions. We will present results obtained on different samples and discuss the promise of this solution for manufacturing testing, whether for in situ process control or end-of-line testing.