Near-perfect measuring of full-field transverse-spatial modes of light

Along with the growing interest in using the transverse-spatial modes of light in quantum and classical optics applications, developing an accurate and efficient measurement method has gained importance. Here, we present a technique relying on a unitary mode conversion for measuring any full-field transverse-spatial mode. Our method only requires three consecutive phase modulations followed by a single mode fiber and is, in principle, error-free and lossless. We experimentally test the technique using a single spatial light modulator and achieve an average error of 4.2% for a set of 9 different full-field Laguerre-Gauss and Hermite-Gauss modes with an efficiency of up to 70%. Moreover, as the method can also be used to measure any complex superposition state, we demonstrate its potential in a quantum cryptography protocol and in high-dimensional quantum state tomography.Comment: 7 pages, 4 figure

Stokes imaging polarimetry using image restoration at the Swedish 1-m Solar Telescope

Aims: We aim to achieve high spatial resolution as well as high polarimetric sensitivity, using an earth-based 1m-class solar telescope, for the study of magnetic fine structure on the Sun. Methods: We use a setup with 3 high-speed, low-noise cameras to construct datasets with interleaved polarimetric states, particularly suitable for Multi-Object Multi-Frame Blind Deconvolution image restorations. We discuss the polarimetric calibration routine as well as various potential sources of error in the results. Results: We obtained near diffraction limited images, with a noise level of approximately 10^(-3) I(cont). We confirm that dark-cores have a weaker magnetic field and at a lower inclination angle with respect to the solar surface than the edges of the penumbral filament. We show that the magnetic field strength in faculae-striations is significantly lower than in other nearby parts of the faculae.Comment: Accepted for publication in Astronomy & Astrophysics, 12 pages, 11 figure

Adaptive pumping for spectral control of random lasers

A laser is not necessarily a sophisticated device: Pumping energy into an amplifying medium randomly filled with scatterers, a powder for instance, makes a perfect "random laser." In such a laser, the absence of mirrors greatly simplifies laser design, but control over emission directionality or frequency tunability is lost, seriously hindering prospects for this otherwise simple laser. Lately, we proposed a novel approach to harness random lasers, inspired by spatial shaping methods recently employed for coherent light control in complex media. Here, we experimentally implement this method in an optofluidic random laser where scattering is weak and modes extend spatially and strongly overlap, making individual selection a priori impossible. We show that control over laser emission can indeed be regained even in this extreme case by actively shaping the spatial profile of the optical pump. This unique degree of freedom, which has never been exploited, allows selection of any desired wavelength and shaping of lasing modes, without prior knowledge of their spatial distribution. Mode selection is achieved with spectral selectivity down to 0.06nm and more than 10dB side-lobe rejection. This experimental method paves the way towards fully tunable and controlled random lasers and can be transferred to other class of lasers.Comment: 23 pages, 7 figure

CT Radiation Dose Optimization and Estimation: an Update for Radiologists

In keeping with the increasing utilization of CT examinations, the greater concern about radiation hazards from examinations has been addressed. In this regard, CT radiation dose optimization has been given a great deal of attention by radiologists, referring physicians, technologists, and physicists. Dose-saving strategies are continuously evolving in terms of imaging techniques as well as dose management. Consequently, regular updates of this issue are necessary especially for radiologists who play a pivotal role in this activity. This review article will provide an update on how we can optimize CT dose in order to maximize the benefit-to-risk ratio of this clinically useful diagnostic imaging method

CT Coronary Angiography with 100kV tube voltage and a low noise reconstruction filter in non-obese patients: evaluation of radiation dose and diagnostic quality of 2D and 3D image reconstructions using open source software (OsiriX)

INTRODUCTION AND PURPOSE. Computed tomography coronary angiography (CTCA) has seen a dramatic evolution in the last decade owing to the availability of multislice CT scanners with 64 detector rows and beyond. However, this evolution has been paralleled by an increase in radiation dose to patients, that can reach extremely high levels (>20mSv) when retrospective ECG-gating techniques are used. On CT angiography, reduction of tube voltage allows to cut radiation dose with improved contrast resolution due to the lower energy of the X-ray beam and increased photoelectric effect. Our purpose is twofold: 1) to evaluate the radiation dose of CTCA studies carried out using a tube voltage of 100kV and a low noise reconstruction filter, compared with a conventional tube voltage of 120kV and a standard reconstruction kernel; 2) to assess the impact of the 100kV acquisition technique on the diagnostic quality of 2D and 3D image reconstructions performed with open source software (OsiriX). MATERIALS AND METHODS. Fifty-one non-obese patients underwent CTCA on a 64-row CT scanner. Out of them, 28 were imaged using a tube voltage of 100kV and a low noise reconstruction filter, while in the remaining 23 patients a tube voltage of 120kV and a standard reconstruction kernel were selected. All CTCA datasets were exported via PACS to a Macintosh™ computer (iMac™) running OsiriX 4.0 (64-bit version), and Maximum Intensity Projection (MIP), Curved Planar Reformation (CPR), and Volume Rendering (VR) views of each coronary artery were generated using a dedicated plug-in (CMIV CTA; Linköping University, Sweden). Diagnostic quality of MIP, CPR, and VR reconstructions was assessed visually by two radiologists with experience in cardiac CT using a three-point score (1=poor, 2=good, 3=excellent). Signal-to-noise ratio (SNR), contrast-to-noise ratio (CNR), intravascular CT density, and effective dose for each group were also calculated. RESULTS. Image quality of VR views was significantly better with the 100kV than with the 120kV protocol (2.77±0.43 vs 2.21±0.85, p=0.0332), while that of MIP and CPR reconstructions was comparable (2.59±0.50 vs 2.32±0.75, p=0.3271, and 2.68±0.48 vs 2.32±0.67, p=0.1118, respectively). SNR and CNR were comparable between the two protocols (16.42±4.64 vs 14.78±2.57, p=0.2502, and 13.43±3.77 vs 12.08±2.10, p=0.2486, respectively), but in the 100kV group aortic root density was higher (655.9±127.2 HU vs 517.2±69.7 HU, p=0.0016) and correlated with VR image quality (rs=0.5409, p=0.0025). Effective dose was significantly lower with the 100kV than with the 120kV protocol (7.43±2.69 mSv vs 18.83±3.60 mSv, p<0.0001). CONCLUSIONS. Compared with a standard tube voltage of 120kV, usage of 100kV and a low noise filter leads to a significant reduction of radiation dose with equivalent and higher diagnostic quality of 2D and 3D reconstructions, respectively in non-obese patients

Efficient DSP and Circuit Architectures for Massive MIMO: State-of-the-Art and Future Directions

Massive MIMO is a compelling wireless access concept that relies on the use of an excess number of base-station antennas, relative to the number of active terminals. This technology is a main component of 5G New Radio (NR) and addresses all important requirements of future wireless standards: a great capacity increase, the support of many simultaneous users, and improvement in energy efficiency. Massive MIMO requires the simultaneous processing of signals from many antenna chains, and computational operations on large matrices. The complexity of the digital processing has been viewed as a fundamental obstacle to the feasibility of Massive MIMO in the past. Recent advances on system-algorithm-hardware co-design have led to extremely energy-efficient implementations. These exploit opportunities in deeply-scaled silicon technologies and perform partly distributed processing to cope with the bottlenecks encountered in the interconnection of many signals. For example, prototype ASIC implementations have demonstrated zero-forcing precoding in real time at a 55 mW power consumption (20 MHz bandwidth, 128 antennas, multiplexing of 8 terminals). Coarse and even error-prone digital processing in the antenna paths permits a reduction of consumption with a factor of 2 to 5. This article summarizes the fundamental technical contributions to efficient digital signal processing for Massive MIMO. The opportunities and constraints on operating on low-complexity RF and analog hardware chains are clarified. It illustrates how terminals can benefit from improved energy efficiency. The status of technology and real-life prototypes discussed. Open challenges and directions for future research are suggested.Comment: submitted to IEEE transactions on signal processin

Simulation of an Axial Vircator

An algorithm of particle-in-cell simulations is described and tested to aid further the actual design of simple vircators working on axially symmetric modes. The methods of correction of the numerical solution, have been chosen and jointly tested, allow the stable simulation of the fast nonlinear multiflow dynamics of virtual cathode formation and evolution, as well as the fields generated by the virtual cathode. The selected combination of the correction methods can be straightforwardly generalized to the case of axially nonsymmetric modes, while the parameters of these correction methods can be widely used to improve an agreement between the simulation predictions and the experimental data.Comment: 9 pages, 3 figure

Scanning protocol optimisation for dual-energy computed tomography angiography in peripheral artery stenting

In this thesis, a novel approach has been proposed to evaluate the optimal scanning protocol for dual energy computed tomography angiography in peripheral arterial stents. This new approach includes evaluation of different protocols and image reconstructions at different energy level, development of the optimal protocol based on lowest radiation dose and acceptable image quality. Furthermore, an optimal contrast medium protocol has been identified in imaging peripheral arterial disease