High Closed Loop Correction Accuracy with a Liquid Crystal Wavefront Corrector

Author(s): Cao Zhao-Liang, Mu Quan-Quan, Hu Li-Fa, Liu Yong-Gang, Peng Zeng-Hui, Xuan Li

Abstract:

“We investigate the accurate control of a liquid crystal wavefront corrector. First, the Gamma correction technique is adopted to amend the nonlinear phase modulation. Then, the control method and wavefront reconstruction are considered. Lastly, a closed loop correction experiment is carried out and a high correction accuracy is obtained with peak to valley (PV) of 0.08λ (λ=632.8nm), the wavefront phase rms 0.015λ, as well as the Strehl ratio of 0.99. The diffraction-limited resolution is achieved.”

Link to Publications Page

Publication: Chinese Physics Letters
Issue/Year: Chinese Physics Letters 2008, Volume 25, Issue 3: 989-992
DOI: 10.1088/0256-307X/25/3/050

Projection display using computer-generated phase screens

Author(s): Neil Collings, Andreas Georgiou, Bill Crossland, and Jamie Christmas

Abstract:

“An approach to a robust and efficient projection display uses phasemodulating screens that reduce computer overhead.”

Link to Publications Page

Publication: SPIE Newsroom
Issue/Year: SPIE Newsroom, 26 February 2008,
DOI: 10.1117/2.1200802.1015

Laser beam shaping for micromaterial processing using a liquid crystal display

Author(s): U. Klug, M. Boyle, F. Friederich, R. Kling, and A. Ostendorf

Abstract:

“The high demand for beam shaping technology by the display industry has lead to higher resolutions, smaller pixel pitch and reduced costs. Nowadays high quality, nematic Liquid Crystal on Silicon microdisplays (LCoS) with resolutions of 1920 × 1080 pixels and 8 µm pixel pitch are available. The optical properties of these microdisplays allow for their application as an adaptive optical element where instantaneous change between arbitrary beam profiles is necessary. Laser material processing which often requires high beam qualities with various beam profiles is one industry where this technology could be applied. In this paper, a compact beam shaping setup and simple characterization methods for practical use of the LCoS at micromachining stations are presented. ”

Link to Publications Page

Publication: SPIE Digital Library
Issue/Year: Proc. SPIE, Vol. 6882, 688207 (2008)
DOI: 10.1117/12.763542

Near-perfect hologram reconstruction with a spatial light modulator

Author(s): Alexander Jesacher, Christian Maurer, Andreas Schwaighofer, Stefan Bernet, and Monika Ritsch-Marte

Abstract:

“We present an implementation method for noiseless holographic projection of precalculated light fields with a spatial light modulator. In the reconstructed image, both the spatial amplitude and phase distributions can be programmed independently. This is achieved by diffracting the light from two successive phase holograms that are located in conjugate Fourier planes. The light path is folded such that the two corresponding phase masks can be displayed side by side at a single phase-only spatial light modulator. Such a device has relevant applications in holographic display-or projection systems, and for optical micromanipulation in laser tweezers.”

Link to Publications Page

Publication: Optics Express
Issue/Year: Optics Express, Vol. 16, Issue 4, pp. 2597-2603
DOI: 10.1364/OE.16.002597

Non-scanning motionless fluorescence three-dimensional holographic microscopy

Author(s): Joseph Rosen and Gary Brooker

Abstract:

“Holography is an attractive imaging technique as it offers the ability to view a complete three-dimensional volume from one image. However, holography is not widely applied to the field of three-dimensional fluorescence microscopic imaging, because fluorescence is incoherent and creating holograms requires a coherent interferometer system. Although scanning one beam of an interferometer pattern across the rear aperture of an objective to excite fluorescence in a specimen overcomes the coherence limitation, the mechanical scanning is complicated, which makes the image capturing slow, and the process is limited to low-numerical-aperture objectives. Here we present the first demonstration of a motionless microscopy system (FINCHSCOPE) based on Fresnel incoherent correlation holography, and its use in recording high-resolution three-dimensional fluorescent images of biological specimens. By using high-numerical-aperture objectives, a spatial light modulator, a CCD camera and some simple filters, FINCHSCOPE enables the acquisition of three-dimensional microscopic images without the need for scanning.”

Link to Publications Page

Publication: Nature Photonics
Issue/Year: Nature Photonics 2, 190 – 195 (2008)
DOI: 10.1038/nphoton.2007.300

Holographic optical tweezers with real-time hologram calculation using a phase-only modulating LCOS-based SLM at 1064 nm

Author(s): Andreas Hermerschmidt, Sven Krüger, Tobias Haist, Susanne Zwick, Michael Warber, Wolfgang Osten

Abstract:

“We present a method that enables the generation of arbitrary positioned dual-beam traps without additional hardware in a single-beam holographic optical tweezers setup. By this approach stable trapping at low numerical aperture and long working distance is realized with an inverse standard research microscope. Simulations and first experimental results are presented. Additionally we present first steps towards using the method to realize a holographic 4pi-microscope. We will also give a detailed analysis of the phase-modulating properties and especially the spatial-frequency dependent diffraction efficiency of holograms reconstructed with the phase-only LCOS spatial light modulator used in our system. Finally, accelerated hologram optimization based on the iterative Fourier transform algorithm is done using the graphics processing unit of a consumer graphics board.”

Link to Publications Page

Publication: SPIE Digital Library
Issue/Year: SPIE Proceedings, Vol. 6905, 690508 (2008),
DOI: 10.1117/12.764649

Stimulated emission depletion microscopy with a supercontinuum source and fluorescence lifetime imaging

Author(s): Egidijus Auksorius, Bosanta R. Boruah, Christopher Dunsby, Peter M. P. Lanigan, Gordon Kennedy, Mark A. A. Neil, and Paul M. W. French

Abstract:

“We demonstrate stimulated emission depletion (STED) microscopy implemented in a laser scanning confocal microscope using excitation light derived from supercontinuum generation in a microstructured optical fiber. Images with resolution improvement beyond the far-field diffraction limit in both the lateral and axial directions were acquired by scanning overlapped excitation and depletion beams in two dimensions using the flying spot scanner of a commercially available laser scanning confocal microscope. The spatial properties of the depletion beam were controlled holographically using a programmable spatial light modulator, which can rapidly change between different STED imaging modes and also compensate for aberrations in the optical path. STED fluorescence lifetime imaging microscopy is demonstrated through the use of time-correlated single photon counting.”

Link to Publications Page

Publication: Optics Letters
Issue/Year: Optics Letters, Vol. 33, Issue 2, pp. 113-115, 2008
DOI: 10.1364/OL.33.000113

Demixing light paths inside disordered metamaterials

Author(s): I. M. Vellekoop, E. G. van Putten, A. Lagendijk, and A. P. Mosk

Abstract:

“We experimentally demonstrate the first method to focus light inside disordered photonic metamaterials. In such materials, scattering prevents light from forming a geometric focus. Instead of geometric optics, we used multi-path interference to make the scattering process itself concentrate light on a fluorescent nanoscale probe at the target position. Our method uses the fact that the disorder in a solid material is fixed in time. Therefore, even disordered light scattering is deterministic. Measurements of the probes fluorescence provided the information needed to construct a specific linear combination of hundreds of incident waves, which interfere constructively at the probe.”

Link to Publications Page

Publication:Optics Express
Issue/Year: Optics Express, Vol. 16, Issue 1, pp. 67-80, 2008
DOI: 10.1364/OE.16.000067

Extended fractional wavelet joint transform correlator

Author(s): Alpana Bhagatji, Naveen K. Nishchal, Arun K. Gupta and B.P. Tyagi

Abstract:

“An extended fractional wavelet joint transform correlator is implemented for real-time target recognition applications. The real-time input scene captured using a charge-coupled device camera along with the reference image is fractional Fourier transformed. The obtained joint power spectrum is multiplied by an appropriately scaled wavelet filter and the resultant function is differentiated. The application of wavelet filter enhances the correlation outputs and differential processing of wavelet-filtered joint power spectrum improves the detection efficiency by reducing the zero-order spectra. Targets with Gaussian and speckle noise have also been used to check the correlation output. The performance metrics: correlation peak intensity, peak-to-correlation energy, peak-to-sidelobe ratio and signal to clutter ratio have been calculated. The experimental results are presented in support of the proposed idea.”

Link to Publications Page

Publication: Optics Communications
Issue/Year: Optics Communications Volume 281, Issue 1, 1 January 2008, Pages 44-48
DOI: 10.1016/j.optcom.2007.09.005

Eigenmodes of a hydrodynamically coupled micron-size multiple-particle ring

Author(s): R. Di Leonardo, S. Keen, J. Leach, C. D. Saunter, G. D. Love, G. Ruocco and M. J. Padgett

Abstract:

“We use a continuous acquisition, high-speed camera with integrated centroid tracking to simultaneously measure the positions of a ring of micron-sized particles held in holographic optical tweezers. Hydrodynamic coupling between the particles gives a set of eigenmodes, each one independently relaxing with a characteristic decay rate (eigenvalue) that can be measured using our positional data. Despite the finite particle size, we find an excellent agreement between the measured eigenvalues and those numerically predicted by Oseen theory applied to the two-dimensional (2D) ring geometry. Particle motions are also analyzed in terms of the alternative eigenmode set obtained by wrapping onto the ring the eigenmodes of a 1D periodic chain. We identify the modes for which the periodic chain is a good approximation to the ring and those for which it is not.”

Link to Publications Page

Publication: Physical Review E
Issue/Year: Phys. Rev. E 76, Issue 6, 061402 (2007)
DOI: 10.1103/PhysRevE.76.061402
1 44 45 46 47 48 57