Position clamping in a holographic counterpropagating optical trap

Optical traps consisting of two counterpropagating, divergent beams of light allow relatively high forces to be exerted along the optical axis by turning off one beam, however the axial stiffness of the trap is generally low due to the lower numerical apertures typically used. Using a high speed spatial light modulator and CMOS camera, we demonstrate 3D servocontrol of a trapped particle, increasing the stiffness from 0.004 to 1.5μNm<sup>−1</sup>. This is achieved in the “macro-tweezers” geometry [Thalhammer, J. Opt. 13, 044024 (2011); Pitzek, Opt. Express 17, 19414 (2009)], which has a much larger field of view and working distance than single-beam tweezers due to its lower numerical aperture requirements. Using a 10×, 0.2NA objective, active feedback produces a trap with similar effective stiffness to a conventional single-beam gradient trap, of order 1μNm<sup>−1</sup> in 3D. Our control loop has a round-trip latency of 10ms, leading to a resonance at 20Hz. This is sufficient bandwidth to reduce the position fluctuations of a 10μm bead due to Brownian motion by two orders of magnitude. This approach can be trivially extended to multiple particles, and we show three simultaneously position-clamped beads

Stable optical trapping and sensitive characterization of nanostructures using standing- wave Raman tweezers

Optical manipulation and label-free characterization of nanoscale structures open up new possibilities for assembly and control of nanodevices and biomolecules. Optical tweezers integrated with Raman spectroscopy allows analyzing a single trapped particle, but is generally less effective for individual nanoparticles. The main challenge is the weak gradient force on nanoparticles that is insufficient to overcome the destabilizing effect of scattering force and Brownian motion. Here, we present standing-wave Raman tweezers for stable trapping and sensitive characterization of single isolated nanostructures with a low laser power by combining a standing-wave optical trap with confocal Raman spectroscopy. This scheme has stronger intensity gradients and balanced scattering forces, and thus can be used to analyze many nanoparticles that cannot be measured with single-beam Raman tweezers, including individual single-walled carbon nanotubes (SWCNT), graphene flakes, biological particles, SERS-active metal nanoparticles, and high-refractive semiconductor nanoparticles. This would enable sorting and characterization of specific SWCNTs and other nanoparticles based on their increased Raman fingerprints

Copyright Law and the Democraticization of Cultural Value

This essay examines and criticizes copyright law as it now functions in Western society. I argue that copyright law only serves corporate interests and functions to limit the development of and use of cultural symbols and texts. In effect, this eliminates the use of cultural texts by marginalized groups. Furthermore, I bring to light several case studies that suggest copyright law does not only hinder the production of cultural material, but is not necessary to facilitate a healthy environment for the production and distribution of cultural material within a given society. Conversely, I suggest that by way of eliminating copyright law altogether, we may expedite a process I call the "democratization of cultural production and exchange". By allowing citizen consumers of cultural products, using new digital technologies, to assign cultural value to cultural texts without the politics and economic injustices that arise from the use and abuse of copyright law, we may have a richer and ultimately more economically sound system by which cultural texts can be generated and shared. In order to defend against those who have similar notions about copyright law as I, but call for the implementation of a limited copyright law, I explain how communities and individual artists can and indeed do thrive while entirely disregarding copyright law. This paper should motivate future scholars to examine in particular the compatibility of outdated copyright law with digital technologies and web-based services. It is suggested through my initial research that these services can and will replace the function of rigid copyright law to help facilitate and incentivize a democratized and streamlined system of cultural production and exchange

The Time-Triggered Sensor Fusion Model

The time-triggered sensor fusion model decom-poses a real time system into three levels, a node level, containing the sensors and the actuators, a cluster level that gathers measurements and per-forms sensor fusion, and an application level where an application program makes control decisions based on an environmental information provided by the cluster level. Because the application code is independent of the employed sensors, the system is open to sensor reconfigurations and reuse of the application code. Furthermore the model contains a hardware-independent application interface and a time-triggered smart transducer network. An application of the presented ideas is shown with a mobile robot controlled by a Time-Triggered Protocol network

Function test environment for embedded driver components. accepted for presentation at the

Abstract — Testing and verification are important methods for gaining confidence in the reliability of a software product. Keeping this confidence up is especially dif-ficult for software that has to follow fast changing development cycles or that is tar-geted at many different platforms. In this paper we present a test framework for specifying, executing, and evaluating function (black-box) tests for I/O control blocks that are part of a Matlab/Simulink based rapid-prototyping (RP) development environment for distributed control appli-cations for the time-triggered network protocol TTP/C. The framework uses the RP environment to create embedded test applications which are then executed in a phys-ical test network. In doing so the test application itself acts as a test driver for the required I/O operations. Results from this application are then compared to refer-ence results that are created by the framework from the simulation and from the test specification. Tests are specified independently of the programming language using a format that was designed for ease-of-use and extensive re-use of components in mind. Concluding we present an implementation of this framework in a resource constrained real-world corporate environment, discussing problems, design decisions, and expe-riences gained during its development and use.