Open AccessFeature PaperReview
Microwave Signal Processing over Multicore Fiber
Photonics 2017, 4(4), 49; doi:10.3390/photonics4040049 -
Abstract
We review the introduction of the space dimension into fiber-based technologies to implement compact and versatile signal processing solutions for microwave and millimeter wave signals. Built upon multicore fiber links and devices, this approach allows the realization of fiber-distributed signal processing in the
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We review the introduction of the space dimension into fiber-based technologies to implement compact and versatile signal processing solutions for microwave and millimeter wave signals. Built upon multicore fiber links and devices, this approach allows the realization of fiber-distributed signal processing in the context of fiber-wireless communications, providing both radiofrequency access distribution and signal processing in the same fiber medium. We present different space-division multiplexing architectures to implement tunable true time delay lines that can be applied to a variety of microwave photonics functionalities, such as signal filtering, radio beamsteering in phased array antennas or optoelectronic oscillation. In particular, this paper gathers our latest work on the following multicore fiber technologies: dispersion-engineered heterogeneous multicore fiber links for distributed tunable true time delay line operation; multicavity devices built upon the selective inscription of gratings in homogenous multicore fibers for compact true time delay line operation; and multicavity optoelectronic oscillation over both homogeneous and heterogeneous multicore fibers. Full article
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Open AccessArticle
Higher-Order Interactions in Quantum Optomechanics: Analytical Solution of Nonlinearity
Photonics 2017, 4(4), 48; doi:10.3390/photonics4040048 -
Abstract
A method is described to solve the nonlinear Langevin equations arising from quadratic interactions in quantum mechanics. While the zeroth order linearization approximation to the operators is normally used, here, first and second order truncation perturbation schemes are proposed. These schemes employ higher-order
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A method is described to solve the nonlinear Langevin equations arising from quadratic interactions in quantum mechanics. While the zeroth order linearization approximation to the operators is normally used, here, first and second order truncation perturbation schemes are proposed. These schemes employ higher-order system operators, and then approximate number operators with their corresponding mean boson numbers only where needed. Spectral densities of higher-order operators are derived, and an expression for the second-order correlation function at zero time-delay has been found, which reveals that the cavity photon occupation of an ideal laser at threshold reaches 62, in good agreement with extensive numerical calculations. As further applications, analysis of the quantum anharmonic oscillator, calculation of Q-functions, analysis of quantum limited amplifiers, and nondemoliton measurements are provided. Full article
Open AccessArticle
Heat Dissipation Schemes in AlInAs/InGaAs/InP Quantum Cascade Lasers Monitored by CCD Thermoreflectance
Photonics 2017, 4(4), 47; doi:10.3390/photonics4040047 -
Abstract
In this paper, we report on the experimental investigation of the thermal performance of lattice matched AlInAs/InGaAs/InP quantum cascade lasers. Investigated designs include double trench, single mesa, and buried heterostructures, which were grown by combined Molecular Beam Epitaxy (MBE) and Metal Organic Vapor
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In this paper, we report on the experimental investigation of the thermal performance of lattice matched AlInAs/InGaAs/InP quantum cascade lasers. Investigated designs include double trench, single mesa, and buried heterostructures, which were grown by combined Molecular Beam Epitaxy (MBE) and Metal Organic Vapor Phase Epitaxy (MOVPE) techniques. The thermal characteristics of lasers are investigated by Charge-Coupled Device CCD thermoreflectance. This method allows for the fast and accurate registration of high-resolution temperature maps of the whole device. We observe different heat dissipation mechanisms for investigated geometries of Quantum Cascade Lasers (QCLs). From the thermal point of view, the preferred design is the buried heterostructure. The buried heterostructures structure and epi-layer down mounting help dissipate the heat generated from active core of the QCL. The experimental results are in very good agreement with theoretical predictions of heat dissipation in various device constructions. Full article
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Open AccessFeature PaperReview
Integrated Microwave Photonics for Wideband Signal Processing
Photonics 2017, 4(4), 46; doi:10.3390/photonics4040046 -
Abstract
We describe recent progress in integrated microwave photonics in wideband signal processing applications with a focus on the key signal processing building blocks, the realization of monolithic integration, and cascaded photonic signal processing for analog radio frequency (RF) photonic links. New developments in
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We describe recent progress in integrated microwave photonics in wideband signal processing applications with a focus on the key signal processing building blocks, the realization of monolithic integration, and cascaded photonic signal processing for analog radio frequency (RF) photonic links. New developments in integration-based microwave photonic techniques, that have high potentialities to be used in a variety of sensing applications for enhanced resolution and speed are also presented. Full article
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Open AccessReview
Tunable Multiband Microwave Photonic Filters
Photonics 2017, 4(4), 45; doi:10.3390/photonics4040045 -
Abstract
The increasing demand for multifunctional devices, the use of cognitive wireless technology to solve the frequency resource shortage problem, as well as the capabilities and operational flexibility necessary to meet ever-changing environment result in an urgent need of multiband wireless communications. Spectral filter
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The increasing demand for multifunctional devices, the use of cognitive wireless technology to solve the frequency resource shortage problem, as well as the capabilities and operational flexibility necessary to meet ever-changing environment result in an urgent need of multiband wireless communications. Spectral filter is an essential part of any communication systems, and in the case of multiband wireless communications, tunable multiband RF filters are required for channel selection, noise/interference removal, and RF signal processing. Unfortunately, it is difficult for RF electronics to achieve both tunable and multiband spectral filtering. Recent advancements of microwave photonics have proven itself to be a promising candidate to solve various challenges in RF electronics including spectral filtering, however, the development of multiband microwave photonic filtering still faces lots of difficulties, due to the limited scalability and tunability of existing microwave photonic schemes. In this review paper, we first discuss the challenges that were facing by multiband microwave photonic filter, then we review recent techniques that have been developed to tackle the challenge and lead to promising developments of tunable microwave photonic multiband filters. The successful design and implementation of tunable microwave photonic multiband filter facilitate the vision of dynamic multiband wireless communications and radio frequency signal processing for commercial, defense, and civilian applications. Full article
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Open AccessFeature PaperReview
Simultaneous Multi-Channel Microwave Photonic Signal Processing
Photonics 2017, 4(4), 44; doi:10.3390/photonics4040044 -
Abstract
Microwave photonic (MWP) systems exploit the advantages of photonics, especially with regards to ultrabroad bandwidth and adaptability, features that are significantly more challenging to obtain in the electronic domain. Thus, MWP systems can be used to realize a number of microwave signal processing
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Microwave photonic (MWP) systems exploit the advantages of photonics, especially with regards to ultrabroad bandwidth and adaptability, features that are significantly more challenging to obtain in the electronic domain. Thus, MWP systems can be used to realize a number of microwave signal processing functions including, amongst others, waveform generation and radio-frequency spectrum analysis (RFSA). In this paper, we review recent results on fiber and integrated approaches for simultaneous generation of multiple chirped microwave waveforms as well as multi-channel RFSA of ultrahigh repetition optical rate pulse trains. Full article
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Open AccessArticle
Design Rules For a Nano-Opto-Mechanical Actuator Based on Suspended Slot Waveguides
Photonics 2017, 4(3), 43; doi:10.3390/photonics4030043 -
Abstract
In this paper, physical modeling including optical and Casimir forces is adopted in order to analyze a nano-opto-mechanical actuator based on silicon-on-insulator suspended slot waveguides. Numerical simulations based on the finite element method and systematic design rules are presented. Moreover, parametric investigations on
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In this paper, physical modeling including optical and Casimir forces is adopted in order to analyze a nano-opto-mechanical actuator based on silicon-on-insulator suspended slot waveguides. Numerical simulations based on the finite element method and systematic design rules are presented. Moreover, parametric investigations on slot waveguide sizes and optical properties are presented, and their influence on the actuator’s features are discussed. Full article
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Open AccessArticle
Totally Vacuum-Free Processed Crystalline Silicon Solar Cells over 17.5% Conversion Efficiency
Photonics 2017, 4(3), 42; doi:10.3390/photonics4030042 -
Abstract
In this work, we introduce a totally vacuum-free cost-efficient crystalline silicon solar cells. Solar cells were fabricated based on low-cost techniques including spin coating, spray pyrolysis, and screen-printing. A best efficiency of 17.51% was achieved by non-vacuum process with a basic structure of
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In this work, we introduce a totally vacuum-free cost-efficient crystalline silicon solar cells. Solar cells were fabricated based on low-cost techniques including spin coating, spray pyrolysis, and screen-printing. A best efficiency of 17.51% was achieved by non-vacuum process with a basic structure of <AI/p+/p−Si/n+/SiO2/TiO2/Ag> CZ-Si p-type solar cells. Short circuit current density (JSC) and open circuit voltage (VOC) of the best cell were measured as 38.1 mA·cm−2 and 596.2 mV, respectively with fill factor (FF) of 77.1%. Suns-Voc measurements were carried out and the detrimental effect of the series resistance on the performance was revealed. It is concluded that higher efficiencies are achievable by the improvements of the contacts and by utilizing good quality starting wafers. Full article
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Open AccessArticle
Mapping Molecular Function to Biological Nanostructure: Combining Structured Illumination Microscopy with Fluorescence Lifetime Imaging (SIM + FLIM)
Photonics 2017, 4(3), 40; doi:10.3390/photonics4030040 -
Abstract
We present a new microscope integrating super-resolved imaging using structured illumination microscopy (SIM) with wide-field optically sectioned fluorescence lifetime imaging (FLIM) to provide optical mapping of molecular function and its correlation with biological nanostructure below the conventional diffraction limit. We illustrate this SIM
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We present a new microscope integrating super-resolved imaging using structured illumination microscopy (SIM) with wide-field optically sectioned fluorescence lifetime imaging (FLIM) to provide optical mapping of molecular function and its correlation with biological nanostructure below the conventional diffraction limit. We illustrate this SIM + FLIM capability to map FRET readouts applied to the aggregation of discoidin domain receptor 1 (DDR1) in Cos 7 cells following ligand stimulation and to the compaction of DNA during the cell cycle. Full article
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Open AccessArticle
Exploring the Potential of Airyscan Microscopy for Live Cell Imaging
Photonics 2017, 4(3), 41; doi:10.3390/photonics4030041 -
Abstract
Biological research increasingly demands the use of non-invasive and ultra-sensitive imaging techniques. The Airyscan technology was recently developed to bridge the gap between conventional confocal and super-resolution microscopy. This technique combines confocal imaging with a 0.2 Airy Unit pinhole, deconvolution and the pixel-reassignment
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Biological research increasingly demands the use of non-invasive and ultra-sensitive imaging techniques. The Airyscan technology was recently developed to bridge the gap between conventional confocal and super-resolution microscopy. This technique combines confocal imaging with a 0.2 Airy Unit pinhole, deconvolution and the pixel-reassignment principle in order to enhance both the spatial resolution and signal-to-noise-ratio without increasing the excitation power and acquisition time. Here, we present a detailed study evaluating the performance of Airyscan as compared to confocal microscopy by imaging a variety of reference samples and biological specimens with different acquisition and processing parameters. We found that the processed Airyscan images at default deconvolution settings have a spatial resolution similar to that of conventional confocal imaging with a pinhole setting of 0.2 Airy Units, but with a significantly improved signal-to-noise-ratio. Further gains in the spatial resolution could be achieved by the use of enhanced deconvolution filter settings, but at a steady loss in the signal-to-noise ratio, which at more extreme settings resulted in significant data loss and image distortion. Full article
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Open AccessArticle
Phase Mask-Based Multimodal Superresolution Microscopy
Photonics 2017, 4(3), 39; doi:10.3390/photonics4030039 -
Abstract
We demonstrate a multimodal superresolution microscopy technique based on a phase masked excitation beam in combination with spatially filtered detection. The theoretical foundation for calculating the focus from a non-paraxial beam with an arbitrary azimuthally symmetric phase mask is presented for linear and
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We demonstrate a multimodal superresolution microscopy technique based on a phase masked excitation beam in combination with spatially filtered detection. The theoretical foundation for calculating the focus from a non-paraxial beam with an arbitrary azimuthally symmetric phase mask is presented for linear and two-photon excitation processes as well as the theoretical resolution limitations. Experimentally this technique is demonstrated using two-photon luminescence from 80 nm gold particle as well as two-photon fluorescence lifetime imaging of fluorescent polystyrene beads. Finally to illustrate the versatility of this technique we acquire two-photon fluorescence lifetime, two-photon luminescence, and second harmonic images of a mixture of fluorescent molecules and 80 nm gold particles with <120 nm resolution (λ/7). Since this approach exclusively relies on engineering the excitation and collection volumes, it is suitable for a wide range of scanning-based microscopies. Full article
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Open AccessArticle
Analytical Model of the Optical Vortex Scanning Microscope with a Simple Phase Object
Photonics 2017, 4(2), 38; doi:10.3390/photonics4020038 -
Abstract
An analytical model of an optical vortex microscope, in which a simple phase object was inserted into the illuminating beam, is presented. In this microscope, the focused vortex beam interacts with an object and transmits the corresponding information to the detection plane. It
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An analytical model of an optical vortex microscope, in which a simple phase object was inserted into the illuminating beam, is presented. In this microscope, the focused vortex beam interacts with an object and transmits the corresponding information to the detection plane. It was shown that the beam at the detection plane can be separated analytically into two parts: a non-disturbed vortex part and an object beam part. The intensity of the non-disturbed part spreads out over the center; hence, the small disturbance introduced by the object can be detected at the image center. A first procedure for recovering information about the object from this set-up was proposed. The theory was verified experimentally. Full article
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Open AccessArticle
Blind Phase Search with Angular Quantization Noise Mitigation for Efficient Carrier Phase Recovery
Photonics 2017, 4(2), 37; doi:10.3390/photonics4020037 -
Abstract
The inherent discrete phase search nature of the conventional blind phase search (C-BPS) algorithm is found to introduce angular quantization noise in its phase noise estimator. The angular quantization noise found in the C-BPS is shown to limit its achievable performance and its
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The inherent discrete phase search nature of the conventional blind phase search (C-BPS) algorithm is found to introduce angular quantization noise in its phase noise estimator. The angular quantization noise found in the C-BPS is shown to limit its achievable performance and its potential low complexity implementation. A novel filtered BPS algorithm (F-BPS) is proposed and demonstrated to mitigate this quantization noise by performing a low pass filter operation on the C-BPS phase noise estimator. The improved performance of the proposed F-BPS algorithm makes it possible to significantly reduce the number of necessary test phases to achieve the C-BPS performance, thereby allowing for a drastic reduction of its practical implementation complexity. The proposed F-BPS scheme performance is evaluated on a 28-Gbaud 16QAM and 64QAM both in simulations and experimentally. Results confirm a substantial improvement of the performance along with a significant reduction of its potential implementation complexity compared to that of the C-BPS. Full article
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Open AccessArticle
Label-Free Saturated Structured Excitation Microscopy
Photonics 2017, 4(2), 36; doi:10.3390/photonics4020036 -
Abstract
Micro- and nanoscale chemical and structural heterogeneities, whether they are intrinsic material properties like grain boundaries or intentionally encoded via nanoscale fabrication techniques, pose a challenge to current material characterization methods. To precisely interrogate the electronic structure of these complex materials systems, spectroscopic
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Micro- and nanoscale chemical and structural heterogeneities, whether they are intrinsic material properties like grain boundaries or intentionally encoded via nanoscale fabrication techniques, pose a challenge to current material characterization methods. To precisely interrogate the electronic structure of these complex materials systems, spectroscopic techniques with high spatial resolution are required. However, conventional optical microscopies are limited to probe volumes of ~200 nm due to the diffraction limit of visible light. While a variety of sub-diffraction-limited techniques have been developed, many rely on fluorescent contrast agents. Herein we describe label-free saturated structured excitation microscopy (LF-SSEM) applicable to nonlinear imaging approaches such as stimulated Raman and pump-probe microscopy. By exploiting the nonlinear sample response of saturated excitation, LF-SSEM provides theoretically limitless resolution enhancement without the need for a photoluminescent sample. Full article
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Open AccessArticle
Evanescently Coupled Rectangular Microresonators in Silicon-on-Insulator with High Q-Values: Experimental Characterization
Photonics 2017, 4(2), 34; doi:10.3390/photonics4020034 -
Abstract
We report on evanescently coupled rectangular microresonators with dimensions up to 20 × 10 μm2 in silicon-on-insulator in an add-drop filter configuration. The influence of the geometrical parameters of the device was experimentally characterized and a high Q value of 13,000 was
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We report on evanescently coupled rectangular microresonators with dimensions up to 20 × 10 μm2 in silicon-on-insulator in an add-drop filter configuration. The influence of the geometrical parameters of the device was experimentally characterized and a high Q value of 13,000 was demonstrated as well as the multimode optical resonance characteristics in the drop port. We also show a 95% energy transfer between ports when the device is operated in TM-polarization and determine the full symmetry of the device by using an eight-port configuration, allowing the drop waveguide to be placed on any of its sides, providing a way to filter and route optical signals. We used the FDTD method to analyze the device and e-beam lithography and dry etching techniques for fabrication. Full article
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Open AccessArticle
Coupling of Surface Plasmon Polariton in Al-Doped ZnO with Fabry-Pérot Resonance for Total Light Absorption
Photonics 2017, 4(2), 35; doi:10.3390/photonics4020035 -
Abstract
Al-doped ZnO (AZO) can be used as an electrically tunable plasmonic material in the near infrared range. This paper presents finite-difference time-domain (FDTD) simulations on total light absorption (TLA) resulting from the coupling of a surface plasmon polariton (SPP) with Fabry-Pérot (F-P) resonance
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Al-doped ZnO (AZO) can be used as an electrically tunable plasmonic material in the near infrared range. This paper presents finite-difference time-domain (FDTD) simulations on total light absorption (TLA) resulting from the coupling of a surface plasmon polariton (SPP) with Fabry-Pérot (F-P) resonance in a three-layer structure consisting of an AZO square lattice hole array, a spacer, and a layer of silver. Firstly, we identified that the surface plasmon polariton (SPP) that will couple to the F-P resonance because of an SPP standing wave in the (1,0) direction of the square lattice. Two types of coupling between SPP and F-P resonance are observed in the simulations. In order to achieve TLA, an increase in the refractive index of the spacer material leads to a decrease in the thickness of the spacer. Additionally, it is shown that the replacement of silver by other, more cost-effective metals has no significance influence on the TLA condition. It is observed in the simulations that post-fabrication tunability of the TLA wavelength is possible via the electrical tunability of the AZO. Finally, electric field intensity distributions at specific wavelengths are computed to further prove the coupling of SPP with F-P resonance. This work will contribute to the design principle for future device fabrication for TLA applications. Full article
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Open AccessArticle
XL-SIM: Extending Superresolution into Deeper Layers
Photonics 2017, 4(2), 33; doi:10.3390/photonics4020033 -
Abstract
Of all 3D-super resolution techniques, structured illumination microscopy (SIM) provides the best compromise with respect to resolution, signal-to-noise ratio (S/N), speed and cell viability. Its ability to achieve double resolution in all three dimensions enables resolving 3D-volumes almost 10× smaller than with a
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Of all 3D-super resolution techniques, structured illumination microscopy (SIM) provides the best compromise with respect to resolution, signal-to-noise ratio (S/N), speed and cell viability. Its ability to achieve double resolution in all three dimensions enables resolving 3D-volumes almost 10× smaller than with a normal light microscope. Its major drawback is noise contained in the out-of-focus-signal, which—unlike the out-of-focus signal itself—cannot be removed mathematically. The resulting “noise-pollution” grows bigger the more light is removed, thus rendering thicker biological samples unsuitable for SIM. By using a slit confocal pattern, we employ optical means to suppress out-of-focus light before its noise can spoil SIM mathematics. This not only increases tissue penetration considerably, but also provides a better S/N performance and an improved confocality. The SIM pattern we employ is no line grid, but a two-dimensional hexagonal structure, which makes pattern rotation between image acquisitions obsolete and thus simplifies image acquisition and yields more robust fit parameters for SIM. Full article
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Open AccessArticle
Photothermal Microscopy for High Sensitivity and High Resolution Absorption Contrast Imaging of Biological Tissues
Photonics 2017, 4(2), 32; doi:10.3390/photonics4020032 -
Abstract
Photothermal microscopy is useful to visualize the distribution of non-fluorescence chromoproteins in biological specimens. Here, we developed a high sensitivity and high resolution photothermal microscopy with low-cost and compact laser diodes as light sources. A new detection scheme for improving signal to noise
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Photothermal microscopy is useful to visualize the distribution of non-fluorescence chromoproteins in biological specimens. Here, we developed a high sensitivity and high resolution photothermal microscopy with low-cost and compact laser diodes as light sources. A new detection scheme for improving signal to noise ratio more than 4-fold is presented. It is demonstrated that spatial resolution in photothermal microscopy is up to nearly twice as high as that in the conventional widefield microscopy. Furthermore, we demonstrated the ability for distinguishing or identifying biological molecules with simultaneous muti-wavelength imaging. Simultaneous photothermal and fluorescence imaging of mouse brain tissue was conducted to visualize both neurons expressing yellow fluorescent protein and endogenous non-fluorescent chromophores. Full article
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Open AccessArticle
High Harmonics with Controllable Polarization by a Burst of Linearly-Polarized Driver Pulses
Photonics 2017, 4(2), 31; doi:10.3390/photonics4020031 -
Abstract
We theoretically explore a scheme for generation of bright circularly and elliptically polarized high-order harmonics by bursts of linearly polarized pulses with a rotating polarization axis. Circularly polarized harmonics are formed if the bursts are comprised of N pulses that uphold an N
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We theoretically explore a scheme for generation of bright circularly and elliptically polarized high-order harmonics by bursts of linearly polarized pulses with a rotating polarization axis. Circularly polarized harmonics are formed if the bursts are comprised of N pulses that uphold an N-fold rotational symmetry, for N > 2. Rotating the polarization axes of the comprising pulses can generate elliptical harmonics with a collectively tunable ellipticity, from circular through elliptic to linear. The method preserves the single-cycle, single-atom and macroscopic physics of ‘standard’ linearly polarized high harmonic generation, with a high yield and cutoff energy. We investigate the method from a time-domain perspective, as well as a photonic perspective, and formulate the energy and spin-angular momentum conservation laws for this scheme. We find that the case of N = 4 is optimal for this method, resulting with the highest conversion efficiency of elliptical photons. The new features of this source offer new applications to helical ultrafast spectroscopy and ellipsometry. Full article
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Open AccessArticle
Polarization Characterization of Soft X-Ray Radiation at FERMI FEL-2
Photonics 2017, 4(2), 29; doi:10.3390/photonics4020029 -
Abstract
The control of polarization state in soft and hard X-ray light is of crucial interest to probe structural and symmetry properties of matter. Thanks to their Apple-II type undulators, the FERMI-Free Electron Lasers are able to provide elliptical, circular or linearly polarized light
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The control of polarization state in soft and hard X-ray light is of crucial interest to probe structural and symmetry properties of matter. Thanks to their Apple-II type undulators, the FERMI-Free Electron Lasers are able to provide elliptical, circular or linearly polarized light within the extreme ultraviolet and soft X-ray range. In this paper, we report the characterization of the polarization state of FERMI FEL-2 down to 5 nm. The results show a high degree of polarization of the FEL pulses, typically above 95%. The campaign of measurements was performed at the Low Density Matter beamline using an electron Time-Of-Flight based polarimeter. Full article
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