3-dimensional imaging often requires substantial effort since information along the optical axis is not straight forward gatherable. In many applications it is aimed for depth information along the direction of view. For example fluidic mixing processes and the environmental interaction on a microscopic scale are of particular importance for e.g. pharmaceutical applications and often demand for 3D information. This problem is often solved by stereoscopic approaches, where two cameras are used in order to gather depth information by triangulation technique. Another approach is to scan the object through the focal plane in order to get sharp images of each layer. Since the before mentioned approaches require a lot of video data to be evaluated it would be more convenient to get depth mapping within a single camera recording and without scanning. Here we present a tunable 3D depth-mapping camera technique in combination with dynamic aberration control. By using an incoherent light source, only one camera and a spatial light modulator (LCoS-SLM), it is a simply applicable and highly scalable technique. A double-helix point spread function (DH-PSF) is generated for light emerging from the observed focal plane. Each object appears as a double-image on the camera. Within the orientation of the double-image, depth information along the optical axis is encoded. By using an additional adaptive element (deformable mirror) the technique is combined with wide-field aberration correction. Here we combine a tunable 3D depth camera with dynamic aberration control in one imaging system.
The availability of spatial light modulators as standard turnkey components and their ongoing development makes them attractive for a huge variety of optical measurement systems in industry and research. Here, we outline two examples of how optical measurements can benefit from spatial light modulators. Ultrasound testing has become an indispensable tool for industrial inspection. Contact-free measurements can be achieved by laser-induced ultrasound. One disadvantage is that due to the highly divergent sound field of the generated shear waves for a point-wise thermoelastic excitation, only a poor spatial selectivity can be achieved. This problem can be solved by creating an ultrasound focus by means of a ring-like laser intensity distribution, but standard fixed-form optical components used for their generation are always optimised to a fixed set of parameters. Here, we demonstrate, how a predefined intensity pattern as e.g. a ring can be created from an arbitrary input laser beam using a phase-retrieval algorithm to shape an ultrasound focus in the sample. By displaying different patterns on the spatial light modulator, the focus can be traversed in all three directions through the object allowing a fast and highly spatially resolving scanning of the sample. Optical measurements take often place under difficult conditions. They are affected by variations of the refractive index, caused e.g. by phase boundaries between two media of different optical density. This will result in an increased measurement uncertainty or, in the worst case, will cause the measurement to fail. To overcome these limitations, we propose the application of adaptive optics. Optical flow velocity measurements based on image correlation in water that are performed through optical distortions are discussed. We demonstrate how the measurement error induced by refractive index variations can be reduced if a spatial light modulator is used in the measurement setup to compensate for the wavefront distortions.