We present a method for shaping point spread functions (PSF) into simple geometric shapes that are free of noise or speckles. The derived phase distributions are intended for typical 2f setups used for reading out computer generated holograms (CGH). Used in conjunction with existing CGH techniques for spot distributions the shaped PSFs can similarly be distributed on a 3D working volume. The PSF's contiguous intensity and phase make them beneficial in many applications such as photo-stimulation, optical manipulation, multi-photon excitation and laser materials processing. This manuscript presents the derivations of the phase functions and their experimental demonstration.
Helico-conical beams (HCBs) are a class of orbital angular momentum (OAM)-carrying beams with spiral phase and intensity profiles. In this communication, we demonstrate the use of a common path interferometer (CPI) to phase-image incoming HCBs and directly detect their OAM-associated properties. The output intensity of the CPI is a direct mapping of the HCB's phase, hence both the topological charge value and sign manifest in the output intensity distribution. The topological charge value is calculated by fringe counting, while the helicity is determined by observing the intensity along the region. With our current CPI setup, we can firmly detect up to l = 20. Higher values of l lead to a decrease in the fringe visibility, but this can in principle be improved by tailoring the parameters of the phase contrast filter (PCF) employed in the CPI. We present analytical expressions to optimize the CPI for HCB charge detection.
Phase-only spatial light modulators (SLM) have been a staple in laser beam shaping research and applications due to their efficiency and programmability. An SLM's capability to shape three-dimensional distributions of light has interesting applications in optical micromanipulation and microscopy. Since these SLMs operate by modifying the phase of incident light, it is common to model their operation using scalar diffraction theory or Fourier optics. In this work, we show how utilizing a ray tracing or geometric optics analysis can produce both interesting and practical results. We have previously shown how to generate laterally shaped beams that do not have the characteristic noise or discontinuities typical of the output generated with iteratively or numerically derived phase distributions. In this work, we extend the geometric approach to three dimensions to form interesting distributions that behave like nondiffracting beams, light sheets and beams that follow spiraling or diagonal paths as they propagate. The analytically derived input phase functions for these beams can be calculated in a straightforward manner. Hence, they are easily encoded and re-configured for SLM applications. Experiments demonstrate these 3D light distributions on a typical 2f holographic configuration, verifying its applicability on existing holographic setups.
After years of working on light-driven trapping and manipulation, we can see that a confluence of developments is now ripe for the emergence of a new area that can contribute to nanobiophotonics-Light Robotics-which combines advances in microfabrication and optical micromanipulation together with intelligent control ideas from robotics, wavefront engineering and information optics. In the Summer 2017 we are publishing a 482 pages edited Elsevier book volume covering the fundamental aspects needed for Light Robotics including optical trapping systems, microfabrication and microassembly as well as underlying theoretical principles and experimental illustrations for optimizing optical forces and torques for Light Robotics.
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