In this paper, we present an optical setup which estimates the radius of curvature of spherical surfaces with the aid of Fizeau interferometry. While the use of Fizeau interferometry to achieve these measurements is wellunderstood in prior art and commercially deployed, we propose a variant of Fizeau interferometry for the same measurements. Our proposed method deploys electronically-controlled tunable focus lenses to perform cats-eye and confocal beam scans with a motion-free scanning system as opposed to a motion-based laser scanning and repositioning system. Eliminating motion from a surface scanning system mitigates system breakdowns related to bulk mechanical motion of optical elements. It also promises to reduce the system cost as well as bulkiness of such interferometric systems. We show the proposed system improvement via the use of a standard tunable focus lens on a legacy commercial Zygo surface curvature measuring system. We demonstrate the operation of the proposed system with experimental data and results using lenses and curved mirrors as samples. For all samples, we compare our measurements from the actively-tunable Fizeau interferometer to baseline measurements from the same original Zygo system using its own zoom lens. The experimental results show an excellent agreement between measurements from the motion-based legacy commercial system and the actively-tunable bulk motionfree system. Future work would focus on characterizing sample surface aberrations by subtracting wavefront aberrations imparted by the tunable focus lens piece.
In this paper, we explore the collimation quality of collimated Gaussian beams generated via the deployment of engineered diffusers. Various aspects of beam propagation through engineered diffusers are explored using results from carefully designed experiments. Raw Gaussian beam is incident on a sample engineered diffuser. The beam is then collimated and propagated over several meters to clearly estimate beam divergence for different test cases. These test cases include raw and focused beams incident on engineered diffusers, the effect on collimation with the use of speckle reducers, and the evolution of the collimated beam wavefront during propagation. To measure and document the spatial coherence properties of beam propagation and its spatial coherence properties after propagating through the engineered diffuser, we measure the beam profile with knife-edge measurement, CCD imaging, and Shack-Hartmann sensor-based wavefront measurements along the beam propagation path. We do so for all different type of beam conditioning before incidence at the engineered diffuser – this includes analyzing the effects of a speckle reducer in the system. We present detailed experimental results and parameters of the propagating collimated beam in the paper. We hope that this paper will lay foundations for our understanding of using engineered diffusers for short distance free-space optical links using a beam collimation approach which is several times optically efficient than a pinhole based spatial filtering-based beam collimation approach.
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