Complementary Speckle Patterns : deterministic interchange of intrinsic vortices and maxima through Scattering Media

Intensity minima and maxima of speckle patterns obtained behind a diffuser are experimentally interchanged by applying a spiral phase delay of charge $\pm 1$ to the impinging coherent beam. This transform arises from the intuitive expectation that a tightly focused beam is so-changed into a vortex beam and vice-versa. The statistics of extrema locations and the intensity distribution of the so-generated "complementary" patterns are characterized by numerical simulations. It is demonstrated experimentally that the incoherent superposition of the three "complementary speckle patterns" yield a synthetic speckle grain size enlarged by a factor $\sqrt{3}$. A cyclic permutation of optical vortices and maxima is unexpectedly observed and discussed.Comment: 9 pages, 9 figure

Single-side access, isotropic resolution and multispectral 3D photoacoustic imaging with rotate-translate scanning of ultrasonic detector array

Photoacoustic imaging can achieve high-resolution three-dimensional visualization of optical absorbers at penetration depths ~ 1 cm in biological tissues by detecting optically-induced high ultrasound frequencies. Tomographic acquisition with ultrasound linear arrays offers an easy implementation of single-side access, parallelized and high-frequency detection, but usually comes with an image quality impaired by the directionality of the detectors. Indeed, a simple translation of the array perpendicularly to its median imaging plane is often used, but results both in a poor resolution in the translation direction and in strong limited view artifacts. To improve the spatial resolution and the visibility of complex structures while keeping a planar detection geometry, we introduce, in this paper, a novel rotate-translate scanning scheme, and investigate the performance of a scanner implemented at 15 MHz center frequency. The developed system achieved a quasi-isotropic uniform 3D resolution of ~170 um over a cubic volume of side length 8.5 mm, i.e. an improvement in the resolution in the translation direction by almost one order of magnitude. Dual wavelength imaging was also demonstrated with ultrafast wavelength shifting. The validity of our approach was shown in vitro. We discuss the ability to enable in vivo imaging for preclinical and clinical studies.Comment: 43 pages, 5 figure

Nanospace and open-source tools for CubeSat preliminary design: review and pedagogical use-case

This paper aims to facilitate getting acquainted with CubeSat preliminary design by presenting a review of open-source tools commonly used during project first steps, and a concrete example. The light but realistic preliminary design framework is based on a real 3U CubeSat use-case, the CREME project, relying on Nanospace and a package of selected Open-Source tools. This example should allow students and non-related field experts to fully grasp the concepts needed to achieve the basics of a typical preliminary design

Calibrated photoacoustic spectrometry with an imaging system

Photoacoustic (PA) contrast agents are usually characterized with spectrophotometry or uncalibrated PA imaging systems, leading to partial assessment of their PA efficacy. To perform calibrated PA spectroscopy with a PA imaging system, we developed a method that both corrects for the spectral energy distribution of excitation light and performs a conversion from arbitrary to spectroscopic units, using a reference solution of cupric sulfate. The method was implemented on an imaging setup based on a tunable laser and a 5MHz ultrasound array. We demonstrated robust calibrated spectroscopy on 15$\mu$L sample volumes of known chromophores and commonly used PA contrast agents, and for multiple samples simultaneously. The detection was linear with the absorption and the sensitivity below 0.08cm-1

Maximizing energy deposition by shaping few-cycle laser pulses

We experimentally investigate the impact of pulse shape on the dynamics of laser-generated plasma in rare gases. Fast-rising triangular pulses with a slower decay lead to early ionization of the gas and depose energy more efficiently than their temporally reversed counterparts. As a result, in both argon and krypton, the induced shockwave as well as the plasma luminescence are stronger. This is due to an earlier availability of free electrons to undergo inverse Bremsstrahlung on the pulse trailing edge. Our results illustrate the ability of adequately tailored pulse shapes to optimize the energy deposition in gas plasmas

Blockchain-Enabled Redundant Fractionated Spacecraft System

Services and applications provided by satellites are continuously improving in terms of quality and diversity, as well as, their complexity. Resilience of traditional monolithic spacecraft is achieved mainly through redundancy, which ex- ponentially increases the complexity of their production, and therefore, their cost. One solution would be to use fragmented spacecraft systems. Redundancy is achieved by nature with local complexity. Furthermore, scalability of such a system is facilitated. However, data transfer and physical communication link between the “fragments” must be addressed. The main challenge of these systems is the management of the network of satellites. Traditional centralised networks, managed by a single entity, have been proven not to be secure, as they generate a common point of failure, susceptible to attacks. Traditional distributed networks, managed by multiple entities, require honest participants and trust between entities, restricting collab- orative mission applications. In the present article, a design for a blockchain-enabled swarm fractionated system managed by multiple trustless entities is proposed. The system is composed of functionally different nano-satellites which perform tasks from different subsystems in order to replicate the functionalities of a monolithic spacecraft. The blockchain nodes are deployed in the satellites and allow sharing of sensor data between the network. A consensus protocol ensures the validity of the shared data. The proposed system has been implemented and evaluated on a local blockchain composed of four Ethereum nodes. We believe that the proposed application opens the way to new collaborative missions between entirely trustless parties, ensuring transparency and cooperation within the system

Enabling Monetization of Depreciating Data on Blockchains

In this paper, we introduce a protocol to securely exchange data on chain while varying its price according to their freshness, maturity and lifetime. The exchange protocol, implemented as a smart contract, is best applied to crowdsourcing systems for fast depreciating digital goods, in which information is publicly shared after a given delay. The smart contract acts as a trusted intermediary to make sure that the funds of a client are delivered to the provider if and only if the data were really transferred. It also ensures that the data will be freely shared on the blockchain when the data has sufficiently depreciated. We demonstrate our work with an available prototype for specific space tracking data exchange