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434 Works

Noise reduction in a laser polarimeter based on discrete waveplate rotations

Israel J. Vaughn & Brian G. Hoover
While several analyses of polarimeter noise-reduction have been published, little data has been presented to support the analytical results, particularly for a laser polarimeter based on measurements taken at discrete, independent rotation angles of two birefringent waveplates. This paper derives and experimentally demonstrates the reduction of both system and speckle noise in this type of laser polarimeter, achieved by optimizing the rotation angles of the waveplates by minimizing the condition numbers of the appropriate matrix...

Noise reduction in a laser polarimeter based on discrete waveplate rotations

Israel J. Vaughn & Brian G. Hoover
While several analyses of polarimeter noise-reduction have been published, little data has been presented to support the analytical results, particularly for a laser polarimeter based on measurements taken at discrete, independent rotation angles of two birefringent waveplates. This paper derives and experimentally demonstrates the reduction of both system and speckle noise in this type of laser polarimeter, achieved by optimizing the rotation angles of the waveplates by minimizing the condition numbers of the appropriate matrix...

Full-wave finite-difference time-domain simulation of electromagnetic cloaking structures

Yan Zhao, Christos Argyropoulos & Yang Hao
This paper proposes a radial dependent dispersive finite-difference time-domain method for the modeling of electromagnetic cloaking structures. The permittivity and permeability of the cloak are mapped to the Drude dispersion model and taken into account in dispersive FDTD simulations. Numerical simulations demonstrate that under ideal conditions, objects placed inside the cloak are ‘invisible’ to external electromagnetic fields. However for the simplified cloak based on linear transformations, the back scattering has a similar level to the...

Full-wave finite-difference time-domain simulation of electromagnetic cloaking structures

Yan Zhao, Christos Argyropoulos & Yang Hao
This paper proposes a radial dependent dispersive finite-difference time-domain method for the modeling of electromagnetic cloaking structures. The permittivity and permeability of the cloak are mapped to the Drude dispersion model and taken into account in dispersive FDTD simulations. Numerical simulations demonstrate that under ideal conditions, objects placed inside the cloak are ‘invisible’ to external electromagnetic fields. However for the simplified cloak based on linear transformations, the back scattering has a similar level to the...

Focal shift in vector Mathieu-Gauss beams

Raul I. Hernandez-Aranda & Julio C. Gutiérrez-Vega
The three dimensional distribution of focused vector Mathieu-Gauss beams (vMG) is studied in the vicinity of the geometrical focus of an unapertured thin lens. We adopt two different intensity based criteria for defining the actual focus. Our analysis confirms the existence of a focal shift towards the lens for this type of beams. The dependence of the focal shift on the different parameters of the beams is discussed in detail. Beams with different states of...

Focal shift in vector Mathieu-Gauss beams

Raul I. Hernandez-Aranda & Julio C. Gutiérrez-Vega
The three dimensional distribution of focused vector Mathieu-Gauss beams (vMG) is studied in the vicinity of the geometrical focus of an unapertured thin lens. We adopt two different intensity based criteria for defining the actual focus. Our analysis confirms the existence of a focal shift towards the lens for this type of beams. The dependence of the focal shift on the different parameters of the beams is discussed in detail. Beams with different states of...

Closed form formula for Mie scattering of nonparaxial analogues of Gaussian beams

Nicole J. Moore & Miguel A. Alonso
A closed form formula is found for the Mie scattering coefficents of incident complex focus beams (which are a nonparaxial generalization of Gaussian beams) with any numerical aperture. This formula takes the compact form of multipoles evaluated at a single complex point. Included are the cases of incident scalar fields as well as electromagnetic fields with many polarizations, such as linear, circular, azimuthal and radial. Examples of incident radially and azimuthally polarized beams are presented.

Closed form formula for Mie scattering of nonparaxial analogues of Gaussian beams

Nicole J. Moore & Miguel A. Alonso
A closed form formula is found for the Mie scattering coefficents of incident complex focus beams (which are a nonparaxial generalization of Gaussian beams) with any numerical aperture. This formula takes the compact form of multipoles evaluated at a single complex point. Included are the cases of incident scalar fields as well as electromagnetic fields with many polarizations, such as linear, circular, azimuthal and radial. Examples of incident radially and azimuthally polarized beams are presented.

Three dimensional imaging with randomly distributed sensors

Mehdi DaneshPanah, Bahram Javidi & Edward A. Watson
As a promising three dimensional passive imaging modality, Integral Imaging (II) has been investigated widely within the research community. In virtually all of such investigations, there is an implicit assumption that the collection of elemental images lie on a simple geometric surface (e.g. flat, concave, etc), also known as pickup surface. In this paper, we present a generalized framework for 3D II with arbitrary pickup surface geometry and randomly distributed sensor configuration. In particular, we...

Three dimensional imaging with randomly distributed sensors

Mehdi DaneshPanah, Bahram Javidi & Edward A. Watson
As a promising three dimensional passive imaging modality, Integral Imaging (II) has been investigated widely within the research community. In virtually all of such investigations, there is an implicit assumption that the collection of elemental images lie on a simple geometric surface (e.g. flat, concave, etc), also known as pickup surface. In this paper, we present a generalized framework for 3D II with arbitrary pickup surface geometry and randomly distributed sensor configuration. In particular, we...

Polarization-sensitive swept-source optical coherence tomography with continuous source polarization modulation

Masahiro Yamanari, Shuichi Makita & Yoshiaki Yasuno
We present fiber-based polarization-sensitive swept-source optical coherence tomography (SS-OCT) based on continuous source polarization modulation. The light source is a frequency swept laser centered at 1.31 µm with a scanning rate of 20 kHz. The incident polarization is modulated by a resonant electro-optic modulator at 33.3 MHz, which is one-third of the data acquisition frequency. The zeroth- and first-order harmonic components of the OCT signals with respect to the polarization modulation frequency have the polarimetric...

Polarization-sensitive swept-source optical coherence tomography with continuous source polarization modulation

Masahiro Yamanari, Shuichi Makita & Yoshiaki Yasuno
We present fiber-based polarization-sensitive swept-source optical coherence tomography (SS-OCT) based on continuous source polarization modulation. The light source is a frequency swept laser centered at 1.31 µm with a scanning rate of 20 kHz. The incident polarization is modulated by a resonant electro-optic modulator at 33.3 MHz, which is one-third of the data acquisition frequency. The zeroth- and first-order harmonic components of the OCT signals with respect to the polarization modulation frequency have the polarimetric...

Fizeau Fourier transform imaging spectroscopy: missing data reconstruction

Samuel T. Thurman & James R. Fienup
Fizeau Fourier transform imaging spectroscopy yields both spatial and spectral information about an object. Spectral information, however, is not obtained for a finite area of low spatial frequencies. A nonlinear reconstruction algorithm based on a gray-world approximation is presented. Reconstruction results from simulated data agree well with ideal Michelson interferometer-based spectral imagery. This result implies that segmented-aperture telescopes and multiple telescope arrays designed for conventional imaging can be used to gather useful spectral data through...

Fizeau Fourier transform imaging spectroscopy: missing data reconstruction

Samuel T. Thurman & James R. Fienup
Fizeau Fourier transform imaging spectroscopy yields both spatial and spectral information about an object. Spectral information, however, is not obtained for a finite area of low spatial frequencies. A nonlinear reconstruction algorithm based on a gray-world approximation is presented. Reconstruction results from simulated data agree well with ideal Michelson interferometer-based spectral imagery. This result implies that segmented-aperture telescopes and multiple telescope arrays designed for conventional imaging can be used to gather useful spectral data through...

Carrier-envelope phase measurement from half-cycle high harmonics

Pengfei Lan, Peixiang Lu, Fang Li, Yuhua Li & Zhenyu Yang
We present an efficient method to observe the high harmonics generated in individual half-cycle of the driving laser pulse by mixing a weak ultraviolet pulse, and then the cutoff of each half-cycle harmonic is imaged. The simulation shows that the information of the driving laser pulse, including the laser intensity, pulse duration and carrier-envelope phase, can be in situ retrieved from the harmonic spectrogram. In addition, our results show that this method also distinguishes the...

Carrier-envelope phase measurement from half-cycle high harmonics

Pengfei Lan, Peixiang Lu, Fang Li, Yuhua Li & Zhenyu Yang
We present an efficient method to observe the high harmonics generated in individual half-cycle of the driving laser pulse by mixing a weak ultraviolet pulse, and then the cutoff of each half-cycle harmonic is imaged. The simulation shows that the information of the driving laser pulse, including the laser intensity, pulse duration and carrier-envelope phase, can be in situ retrieved from the harmonic spectrogram. In addition, our results show that this method also distinguishes the...

Generation of vortex beams from lasers with controlled Hermite- and Ince-Gaussian modes

Takayuki Ohtomo, Shu-Chun Chu & Kenju Otsuka
We report selective excitations of higher-order Hermite-Gaussian and Ince-Gaussian (IG) modes in a laser-diode-pumped microchip solid-state laser and controlled generation of corresponding higher-order and multiple optical vortex beams of different shapes using an astigmatic mode converter (AMC). Simply changing the pump-beam diameter, shape, and lateral off-axis position of the tight pump beam focus on the laser crystal within a microchip semispherical cavity can produce the desired optical vortex beams in a well controlled manner. Pattern...

Generation of vortex beams from lasers with controlled Hermite- and Ince-Gaussian modes

Takayuki Ohtomo, Shu-Chun Chu & Kenju Otsuka
We report selective excitations of higher-order Hermite-Gaussian and Ince-Gaussian (IG) modes in a laser-diode-pumped microchip solid-state laser and controlled generation of corresponding higher-order and multiple optical vortex beams of different shapes using an astigmatic mode converter (AMC). Simply changing the pump-beam diameter, shape, and lateral off-axis position of the tight pump beam focus on the laser crystal within a microchip semispherical cavity can produce the desired optical vortex beams in a well controlled manner. Pattern...

Characterisation of periodically poled materials using nonlinear microscopy

John Harris, Greg Norris & Gail McConnell
Periodically poled crystalline materials are extremely attractive for processes such as second harmonic generation and optical parametric generation due to their very high conversion efficiency. For optimal performance, fabrication of poled regions with sub-micron tolerance is required. In this paper we introduce multi-photon laser scanning luminescence microscopy as a powerful minimally-invasive measurement technique which provides information about internal device structure with high spatial resolution that cannot be easily obtained with existing methods. A comparative study...

Characterisation of periodically poled materials using nonlinear microscopy

John Harris, Greg Norris & Gail McConnell
Periodically poled crystalline materials are extremely attractive for processes such as second harmonic generation and optical parametric generation due to their very high conversion efficiency. For optimal performance, fabrication of poled regions with sub-micron tolerance is required. In this paper we introduce multi-photon laser scanning luminescence microscopy as a powerful minimally-invasive measurement technique which provides information about internal device structure with high spatial resolution that cannot be easily obtained with existing methods. A comparative study...

Optical vortex trap for resonant confinement of metal nanoparticles

Maria Dienerowitz, Michael Mazilu, Peter J. Reece, Thomas F. Krauss & Kishan Dholakia
The confinement and controlled movement of metal nanoparticles and nanorods is an emergent area within optical micromanipulation. In this letter we experimentally realise a novel trapping geometry near the plasmon resonance using an annular light field possessing a helical phasefront that confines the nanoparticle to the vortex core (dark) region. We interpret our data with a theoretical framework based upon the Maxwell stress tensor formulation to elucidate the total forces upon nanometric particles near the...

Optical vortex trap for resonant confinement of metal nanoparticles

Maria Dienerowitz, Michael Mazilu, Peter J. Reece, Thomas F. Krauss & Kishan Dholakia
The confinement and controlled movement of metal nanoparticles and nanorods is an emergent area within optical micromanipulation. In this letter we experimentally realise a novel trapping geometry near the plasmon resonance using an annular light field possessing a helical phasefront that confines the nanoparticle to the vortex core (dark) region. We interpret our data with a theoretical framework based upon the Maxwell stress tensor formulation to elucidate the total forces upon nanometric particles near the...

Full phase and amplitude control of holographic optical tweezers with high efficiency

Alexander Jesacher, Christian Maurer, Andreas Schwaighofer, Stefan Bernet & Monika Ritsch-Marte
Recently we demonstrated the applicability of a holographic method for shaping complex wavefronts to spatial light modulator (SLM) systems. Here we examine the potential of this approach for optical micromanipulation. Since the method allows one to shape both amplitude and phase of a trapping light field independently and thus provides full control over scattering and gradient forces, it extends the possibilities of commonly used holographic tweezers systems. We utilize two cascaded phase-diffractive elements which can...

Full phase and amplitude control of holographic optical tweezers with high efficiency

Alexander Jesacher, Christian Maurer, Andreas Schwaighofer, Stefan Bernet & Monika Ritsch-Marte
Recently we demonstrated the applicability of a holographic method for shaping complex wavefronts to spatial light modulator (SLM) systems. Here we examine the potential of this approach for optical micromanipulation. Since the method allows one to shape both amplitude and phase of a trapping light field independently and thus provides full control over scattering and gradient forces, it extends the possibilities of commonly used holographic tweezers systems. We utilize two cascaded phase-diffractive elements which can...

Quantification of in vivo autofluorescence dynamics during renal ischemia and reperfusion under 355 nm excitation

Rajesh N. Raman, Christopher D. Pivetti, Dennis L. Matthews, Christoph Troppmann & Stavros G. Demos
We explore a method to quantitatively assess the ability of in vivo autofluorescence as a means to quantify the progression of longer periods of renal warm ischemia and reperfusion in a rat model. The method employs in vivo monitoring of tissue autofluorescence arising mainly from NADH as a means to probe the organ’s function and response to reperfusion. Clinically relevant conditions are employed that include exposure of the kidney to ischemia on the order of...

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  • 2008
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  • figshare Academic Research System
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