Generation of fractal speckles by means of a spatial light modulator

Author(s): Hideki Funamizu and Jun Uozumi

Abstract:

“It was shown in previous studies that, when a diffuser is illuminated by coherent light with an average spatial intensity distribution obeying a negative power function, the scattered field in the Fraunhofer diffraction region exhibits random fractal properties. The method employed so far for producing such fields has a disadvantage in that generated speckle intensities are low due to small transmittance of fractal apertures used in the illumination optics. To overcome this disadvantage, a generation of fractal speckles by means of a spatial light modulator is proposed. The principle is explained and experimental results are also shown.”

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Publication: Optics Express
Issue/Year: Optics Express, Vol. 15, Issue 12, pp. 7415-7422 (2007)
DOI: 10.1364/OE.15.007415

Depth Analysis of Polymer-Coated Steel Samples Using Near-Infrared Femtosecond Laser Ablation Inductively Coupled Plasma Mass Spectrometry

Author(s): M. Paz Mateo, Carmen C. Garcia, R. Hergenröder

Abstract:

“The viability of near-infrared femtosecond laser ablation (fs-LA) inductively coupled plasma mass spectrometry (ICPMS) for the in-depth analysis of polymer coatings over galvanized steel substrates has been studied. A good depth resolution was obtained modifying the femtosecond Gaussian beam to a flat-top beam by using a liquid-crystal display. In order to avoid mixing of information coming from successive shots, a low repetition rate was accomplished and signals were monitored shot by shot. Different kinds of coatings were used to demonstrate the capability of femtosecond ablation for depth-profiling analysis. Ablation was conducted under He atmosphere, after sample cell Ar was admixed. The depth profiles obtained by LA-ICPMS are in good agreement with those obtained by GD-OES for the three analyzed samples. In cases where due to averaging over several millimeter sample roughness determines the depth resolution of GD-OES, it was found that LA-ICPMS achieves better depth resolution due to the better lateral resolution. The depth resolution obtained by LA-ICPMS was found to be 240 nm and 2.3 μm, for a hot-dip galvanized steel (HDGS) and a polymer−polymer-coated HDGS, respectively, compared to the 2.2 and 4.5 μm achieved with GD-OES for the same samples. ”

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Publication:Analytical Chemistry
Issue/Year: Anal. Chem., 2007, 79 (13), pp 4908–4914
DOI: 10.1021/ac070241q

Holographic recording in Fe:Ce:Ti doped LiNbO3 crystal

Author(s): Ravinder Kumar Banyal, B. Raghavendra Prasad

Abstract:

“High diffraction efficiency measurements in a triply doped Fe:Ce:Ti–LiNbO3 crystal are reported. The crystal shows an improved recording sensitivity, weak light-induced scattering and extremely slow readout erasure which makes it highly desirable for non-volatile data storage applications. The suitability of the crystal was demonstrated by high quality holographic recording and retrieval of several astronomical images using shift and rotational multiplexing scheme.”

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Publication: Optics Communications
Issue/Year:Optics Communications, Volume 274, Issue 2, 15 June 2007, Pages 300-306
DOI: 10.1016/j.optcom.2007.02.029

Efficient compensation of Zernike modes and eye aberration patterns using low-cost spatial light modulators

Author(s): Vicente Durán, Vicent Climent, Enrique Tajahuerce, Zbigniew Jaroszewicz, Justo Arines and Salvador Bará

Abstract:

“Off-the-shelf spatial light modulators (SLMs) like those commonly included in video projection devices have been seldom used for the compensation of eye aberrations, mainly due to the relatively low dynamic range of the phase retardation that can be introduced at each pixel. They present, however, some interesting features, such as high spatial resolution, easy handling, wide availability, and low cost. We describe an efficient four-level phase encoding scheme that allows us to use conventional SLMs for compensating optical aberrations as those typically found in human eyes. Experimental results are obtained with artificial eyes aberrated by refractive phase plates introducing either single Zernike terms or complex eye aberration patterns. This proof-of-concept is a step toward the use of low-cost, general purpose SLMs for the compensation of eye aberrations. ”

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Publication: SPIE Journal of Biomedical Optics
Issue/Year: J. Biomed. Opt., Vol. 12, 014037 (2007);
DOI: 10.1117/1.2698048

Wavelet-modified fringe-adjusted joint transform correlator

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

Abstract:

“In this paper, we implement a wavelet-modified fringe-adjusted joint transform correlator (JTC) for real-time target recognition applications. In real-time situation the input scene is captured using a CCD/thermal camera. The obtained joint power spectrum is multiplied with a pre-synthesized fringe-adjusted filter and the resultant function is processed with an appropriately scaled wavelet filter. The wavelet-modified fringe-adjusted JTC has been found to yield better results in comparison to the conventional fringe-adjusted JTC. To suppress the undesired strong dc, the resultant function is differentiated. Differential processing the wavelet-modified fringe-adjusted joint power spectrum removes the zero-order spectra and hence improves the detection efficiency. To focus the correlation terms in different planes in order to capture one of the desired autocorrelation peaks and discard the strong dc and another autocorrelation peak, chirp-encoding technique has also been applied. Computer simulation and experimental results are presented. ”

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Publication: SPIE Proceedings
Issue/Year: Proc. SPIE, Vol. 6405, 640513 (2006);
DOI: 10.1117/12.697891

Polarization encoding and multiplexing of two-dimensional signals: application to image encryption

Author(s): Unnikrishnan Gopinathan, Thomas J. Naughton, and John T. Sheridan

Abstract:

“We discuss an optical system that encodes an input signal to a polarization state, using a spatial light modulator (SLM). Using two SLMs the optical system multiplexes two 2D signals in the polarization domain, and we demonstrate the multiplexing of two binary images. The encryption and decryption of two binary images using an xor operation is also presented.”

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Publication: Applied Optics
Issue/Year: Applied Optics, Vol. 45, Issue 22, pp. 5693-5700, 2006
DOI: 10.1364/AO.45.005693

Numerical analysis of systematic errors in an optical encryption system

Author(s): David S. Monaghan, Unnikrishnan Gopinathan, Damien P. Kelly, Thomas J. Naughton, John T. Sheridan

Abstract:

“We consider a double random phase encoding Encryption/Decryption system in which the image encryption/decryption process is performed numerically. In this paper we look at the effect of quantisation in the decryption process due to the discrete values which a spatial light modulator can display. We look at the characterisation of a transmissive spatial light modulator and we present results from simulations of the system.”

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Publication: SPIE Proceedings
Issue/Year: Proc. SPIE, Vol. 6187, 61870X (2006)
DOI: 10.1117/12.663063

Real-time digital holographic beam-shaping system with a genetic feedback tuning loop

Author(s): Joonku Hahn, Hwi Kim, Kyongsik Choi, and Byoungho Lee

Abstract:

“A novel implementation of a real-time digital holographic system with a genetic feedback tuning loop is proposed. The proposed genetic feedback tuning loop is effective in encoding optimal phase holograms on a liquid-crystal spatial light modulator in the system. Optimal calibration of the liquid-crystal spatial light modulator can be achieved via the genetic feedback tuning loop, and the optimal phase hologram can then overcome the aberration of the internal optics of the system.”

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Publication: Applied Optics
Issue/Year: Applied Optics, Vol. 45, Issue 5, pp. 915-924, 2006
DOI: 10.1364/AO.45.000915

Femtosecond laser ablation elemental mass spectrometry

Author(s): Roland Hergenröder, Ota Samek, Vanja Hommes

Abstract:

“Laser ablation mass spectrometry (LA-MS) has always been an interesting method for the elemental analysis of solid samples. Chemical analysis with a laser requires small amounts of material. Depending on the analytical detection system, subpicogram quantities may be sufficient. In addition, a focused laser beam permits the spatial characterization of heterogeneity in solid samples typically with micrometer resolution in terms of lateral and depth dimensions. With the advent of high-energy, ultra-short pulse lasers, new possibilities arise. The task of this review is to discuss the principle differences between the ablation process of short (>1 ps) and ultra-short (<1 ps) pulses. Based on the timescales and the energy balance of the process that underlies an ablation event, it will be shown that ultra-short pulses are less thermal and cause less collateral damages than longer pulses. The confinement of the pulse energy to the focal region guarantees a better spatial resolution in all dimensions and improves the analytical figures of merit (e.g., fractionation). Applications that demonstrate these features and that will be presented are in-depth profiling of multi-layer samples and the elemental analysis of biological materials.”

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Publication: Mass Spectrometry Reviews
Issue/Year: Mass Spectrometry Reviews, Volume 25, Issue 4 , Pages 551 – 572 (2005)
DOI: 10.1002/mas.20077

Accurate encoding of arbitrary complex fields with amplitude-only liquid crystal spatial light modulators

Author(s): Victor Arrizón, Guadalupe Méndez, and David Sánchez-de-La-Llave

Abstract:

“We show that computer generated holograms, implemented with amplitude-only liquid crystal spatial light modulators, allow the synthesis of fully complex fields with high accuracy. Our main discussion considers modified amplitude holograms whose transmittance is obtained by adding an appropriate bias function to the real cosine computer hologram of the encoded signal. We first propose a bias function, given by a soft envelope of the signal modulus, which is appropriate for perfect amplitude modulators. We also consider a second bias term, given by a constant function, which results appropriate for modulators whose amplitude transmittance is coupled with a linear phase modulation. The influence of the finite pixel size of the spatial light modulator is compensated by digital pre-filtering of the encoded complex signal. The performance of the discussed amplitude CGHs is illustrated by means of numerical simulations and the experimental synthesis of high order Bessel beams.”

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Publication: Optics Express
Issue/Year: Optics Express, Vol. 13, Issue 20, pp. 7913-7927, 2005
DOI: 10.1364/OPEX.13.007913