Determination of wavefront structure for a Hartmann Wavefront Sensor using a phase-retrieval method

Author(s): A. Polo, V. Kutchoukov, F. Bociort, S.F. Pereira, and H.P. Urbach Abstract: “We apply a phase retrieval algorithm to the intensity pattern of a Hartmann wavefront sensor to measure with enhanced accuracy the phase structure of a Hartmann hole array. It is shown that the rms wavefront error achieved by phase reconstruction is one order of magnitude smaller than the one obtained from a typical centroid algorithm. Experimental results are consistent with a phase measurement performed independently using a Shack-Hartmann wavefront sensor.” Link to Publications Page Publication: Optics Express, (free download) Issue/Year/DOI: Optics Express, Vol. 20, Issue 7, pp….

Nonimaging speckle interferometry for high-speed nanometer-scale position detection

Author(s): E. G. van Putten, A. Lagendijk, and A. P. Mosk Abstract: “We experimentally demonstrate a nonimaging approach to displacement measurement for complex scattering materials. By spatially controlling the wavefront of the light that incidents on the material, we concentrate the scattered light in a focus on a designated position. This wavefront acts as a unique optical fingerprint that enables precise position detection of the illuminated material by simply measuring the intensity in the focus. By combining two fingerprints we demonstrate position detection along one in-plane dimension with a displacement resolution of 2.1 nm. As our approach does not require…

Fabrication of three-dimensional electrospun microstructures using phase modulated femtosecond laser pulses

Author(s): Nathan J. Jenness, Yiquan Wu, Robert L. Clark. Abstract: “Electrospun polycaprolactone nanofibers were selectively ablated to form microstructures via the phase modulation of femtosecond laser beams. Ablation width (1–15 μm) and depth (15–110 μm) resolution were dependent upon the selection of pulse energy and microscope objective. Because phase modulation shapes light in a maskless fashion, desired templates were digitally created and physically transferred to electrospun mats within a matter of minutes. Several microarchitectures were formed in parallel by dividing pulse energy between multiple foci, substantially increasing throughput. The data presented herein demonstrates that phase-based laser ablation can be used…

Fabrication of microscale medical devices by two-photon polymerization with multiple foci via a spatial light modulator

Author(s): Shaun D. Gittard, Alexander Nguyen, Kotaro Obata, Anastasia Koroleva, Roger J. Narayan, and Boris N. Chichkov. Abstract: “Two-photon polymerization is an appealing technique for producing microscale devices due to its flexibility in producing structures with a wide range of geometries as well as its compatibility with materials suitable for biomedical applications. The greatest limiting factor in widespread use of two-photon polymerization is the slow fabrication times associated with line-by-line, high-resolution structuring. In this study, a recently developed technology was used to produce microstructures by two-photon polymerization with multiple foci, which significantly reduces the production time. Computer generated hologram pattern…

Coaxial holographic encoding based on pure phase modulation

Author(s): Wei Jia, Zhongyu Chen, Fung Jacky Wen, Changhe Zhou, Yuk Tak Chow, and Po Sheun Chung Abstract: “We describe a simple technique for coaxial holographic image recording and reconstruction, employing a spatial light modulator (SLM) modified in pure phase mode. In the image encoding system, both the reference beam in the outside part and the signal beam in the inside part are displayed by an SLM based on the twisted nematic LCD. For a binary image, the part with amplitude of “1” is modulated with random phase, while the part with amplitude of “0” is modulated with constant phase….

Implementation of phase-shift patterns using a holographic projection system with phase-only diffractive optical elements

Author(s): Wei-Feng Hsu, Yu-Wen Chen, and Yuan-Hong Su Abstract: “We proposed a method to implement spatial phase-shift patterns with subdiffraction limited features through a holographic projection system. The input device of the system displayed phase-only diffractive optical elements that were calculated using the iterative Fourier-transform algorithm with the dummy-area method. By carefully designing the target patterns to the algorithm, the diffractive optical elements generated the Fourier-transformed images containing the phase-shift patterns in which the widths of dark lines were smaller than the diffraction limit. With these demonstrations, we have successfully shown that the near-field phase-shift lithographic technique can be realized…

Recursive wavefront aberration correction method for LCoS spatial light modulators

Author(s): J. García-Márquez, J.E.A. Landgrave, N. Alcalá-Ochoa, C. Pérez-Santos Abstract: “We present two accurate and relatively simple interferometric methods for the correction of wavefront aberrations of about 3 wavelengths (3λ) in spatial light modulators (SLMs) of the liquid crystal on silicon (LCoS) type. The first is based on a recursive use of a wavefront fitting algorithm in a Wyko™ interferometer, in which Zernike polynomials are employed as the basis functions. We show here that the successive use of only three measurements is required to obtain a peak-to-valley (PV) error as low as λ/10, with an uncertainty of λ/30, in the…

Aberration compensation using a spatial light modulator LCD

Author(s): R. Amézquita, O. Rincón and Y. M. Torres Abstract: “The dynamic correction of aberrations introduced in optical systems have been a widely discussed topic in the past 10 years. Adaptive optics is the most important developed field where the Shack-Hartmann sensors and deformable mirrors are used for the measurement and correction of wavefronts. In this paper, an interferometric set-up which uses a Spatial Light Modulator (SLM) as an active element is proposed. Using this SLM a procedure for the compensation of all phase aberrations present in the experimental setup is shown.” Link to Publications Page Publication: Journal of Physics:…

Frequency bandwidth of light focused through turbid media

Author(s): Frerik van Beijnum, Elbert G. van Putten, Ad Lagendijk, and Allard P. Mosk Abstract: “We study the effect of frequency detuning on light focused through turbid media. By shaping the wavefront of the incident beam light is focused through an opaque scattering layer. When detuning the laser we observe a gradual decrease of the focus intensity, while the position, size,and shape of the focus remain the same within experimental accuracy. The frequency dependence of the focus intensity follows a measured speckle correlation function. We support our experimental findings with calculations based on transport theory. Our results imply wavefront shaping…

Application of cooled spatial light modulator for high power nanosecond laser micromachining

Author(s): Rainer J. Beck, Jonathan P. Parry, William N. MacPherson, Andrew Waddie, Nick J. Weston, Jonathan D. Shephard, and Duncan P. Hand Abstract: “The application of a commercially available spatial light modulator (SLM) to control the spatial intensity distribution of a nanosecond pulsed laser for micromachining is described for the first time. Heat sinking is introduced to increase the average power handling capabilities of the SLM beyond recommended limits by the manufacturer. Complex intensity patterns are generated, using the Inverse Fourier Transform Algorithm, and example laser machining is demonstrated. The SLM enables both complex beam shaping and also beam steering.”…

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