Form determination of optical surfaces by measuring the spatial coherence function using shearing interferometry.

We present a new method for the form measurement of optical surfaces using the spatial coherence function, which enables a shearing interferometer in combination with an LED multispot illumination to function as a measurement device. A new evaluation approach connects the measured data with the surface form by inverse raytracing. First measurement results with the inverse evaluation procedures are shown. We present the whole measurement in combination with the evaluation procedure. In addition, the convergence and stability of the implemented optimization task is investigated.

Sparse light fields in coherent optical metrology [Invited].

In this publication, we demonstrate that recording the mutual intensity, instead of a wavefront, enables interferometric measurements with multiple independent light sources at the same time. This scheme can, for example, be used to overcome the problem of a limited acceptance angle of imaging systems in interferometry. We further show that, for a finite number of light sources, measuring a subspace of the mutual intensity equals the recording of the corresponding light field, which is sparse in phase space. This recording modality offers more flexibility with respect to the trade-off between angular multiplexing and spatial resolution than the state of the art, because it is not restricted by the geometric properties of a microlens array, but rather allows arbitrary sampling of the light field.

Laboratory drop towers for the experimental simulation of dust-aggregate collisions in the early solar system.

For the purpose of investigating the evolution of dust aggregates in the early Solar System, we developed two vacuum drop towers in which fragile dust aggregates with sizes up to ~10 cm and porosities up to 70% can be collided. One of the drop towers is primarily used for very low impact speeds down to below 0.01 m/sec and makes use of a double release mechanism. Collisions are recorded in stereo-view by two high-speed cameras, which fall along the glass vacuum tube in the center-of-mass frame of the two dust aggregates. The other free-fall tower makes use of an electromagnetic accelerator that is capable of gently accelerating dust aggregates to up to 5 m/sec. In combination with the release of another dust aggregate to free fall, collision speeds up to ~10 m/sec can be achieved. Here, two fixed high-speed cameras record the collision events. In both drop towers, the dust aggregates are in free fall during the collision so that they are weightless and match the conditions in the early Solar System.