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of interest? did any of you try this one already?

Theoretized 80 years ago was Breit-Wheeler pair production in which two photons result in an electron-positron pair (via a virtual electron). It is a relatively simple Feynmann diagram, but the problem is/was how to produce in practice a high energy photon-photon collider... The collider experiment that the scientists have proposed involves two key steps. First, the scientists would use an extremely powerful high-intensity laser to speed up electrons to just below the speed of light. They would then fire these electrons into a slab of gold to create a beam of photons a billion times more energetic than visible light. The next stage of the experiment involves a tiny gold can called a hohlraum (German for 'empty room'). Scientists would fire a high-energy laser at the inner surface of this gold can, to create a thermal radiation field, generating light similar to the light emitted by stars. They would then direct the photon beam from the first stage of the experiment through the centre of the can, causing the photons from the two sources to collide and form electrons and positrons. It would then be possible to detect the formation of the electrons and positrons when they exited the can. Now this is a good experiment... :)

True, but isnt it E2=(pc)^2 + (m0c^2)^2 such that for photons E\propto{pc} and for mass E\propto{mc^2}. I agree it will take a lot of energy, but this assumes that that wont be the problem at least. The question therefore is whether the mass flow of the photon rocket (fuel consumed to create photons, eg fission/fusion) is higher/lower than the mass flow for e-p creation. You are probably right that the low e-p cross-section will favour direct use of photons to create low thrust for long periods of time, but with significant power available the ISP might be higher for e-p pair creation.

In essence the equation tells you that for photons with zero rest mass m0 all the energy will be converted to momentum of the particles. If you want to accelerate e-p then you first spend part of the energy on creating them (~511 keV each) and you can only use the remaining energy to accelerate them. In this case the equation gives you a lower particle momentum which leads to lower thrust (even when assuming 100% acceleration efficiency). ISP is a tricky concept in this case because there are different definitions which clash in the relativistic context (due to the concept of mass flow). R. Tinder gets to a I_SP = c (speed of light) for a photon rocket (using the relativistic mass of the photons) which is the maximum possible relativistic I_SP: http://goo.gl/Zz5gyC .

The problem is that the light cone angle has a limit - all particles with high momentum (mass x velocity) generate light cones with the same angle. Hence, these particles are indistinguishable. Now Chalmers researcher Philippe Tassin and his colleagues at the Free University of Brussels have designed a material that manipulates the Cherenkov cone so that also particles with high momentum get a distinct light cone angle too. The work is on the cover of this week's issue of the journal Physical Review Letters ("Controlling Cherenkov Radiation with Transformation-Optical Metamaterials").

The first complete theory of how plasmons produce "hot carriers" has been developed by researchers in the US. The new model could help make this process of producing carriers more efficient, which would be good news for enhancing solar-energy conversion in photovoltaic devices.

I did not read the paper but what is further down written in the article, does not give much hope that this actually gives much more insight than what we had nor that it could be used in any way to improve current PV cells soon: e.g. "To fully exploit these carriers for such applications, researchers need to understand the physical processes behind plasmon-induced hot-carrier generation. Nordlander's team has now developed a simple model that describes how plasmons produce hot carriers in spherical silver nanoparticles and nanoshells. The model describes the conduction electrons in the metal as free particles and then analyses how plasmons excite hot carriers using Fermi's golden rule - a way to calculate how a quantum system transitions from one state into another following a perturbation. The model allows the researchers to calculate how many hot carriers are produced as a function of the light frequency used to excite the metal, as well as the rate at which they are produced. The spectral profile obtained is, to all intents and purposes, the "plasmonic spectrum" of the material. Particle size and hot-carrier lifetimes "Our analyses reveal that particle size and hot-carrier lifetimes are central for determining both the production rate and the energies of the hot carriers," says Nordlander. "Larger particles and shorter lifetimes produce more carriers with lower energies and smaller particles produce fewer carriers, but with higher energies."

Like it! Can you do an initial assessment on space applications Jojo?

NASA Releases Tool Enabling Citizen Scientists to Examine Asteroid Vesta Vesta Trek is a free, web-based application that provides detailed visualizations of Vesta, one of the largest asteroids in our solar system. NASA's Dawn spacecraft studied Vesta from July 2011 to September 2012. Data gathered from multiple instruments aboard Dawn have been compiled into Vesta Trek's user-friendly set of tools, enabling citizen scientists and students to study the asteroid's features. The application includes: -- Interactive maps with the ability to overlay a growing range of data sets including topography, mineralogy, abundance of elements and geology, as well as analysis tools for measuring the diameters, heights and depths of surface features and more. -- 3-D printer-exportable topography so users can print physical models of Vesta's surface. -- Standard keyboard gaming controls to manoever a first-person visualization of "flying" across the surface of the asteroid. "There's nothing like seeing something with your own eyes, but these types of detailed data-visualizations are the next best thing," said Kristen Erickson, Director, Science Engagement and Partnerships at NASA Headquarters in Washington DC.

More arguments for a lunar base? "They found the most mass-efficient path involves launching a crew from Earth with just enough fuel to get into orbit around the Earth. A fuel-producing plant on the surface of the moon would then launch tankers of fuel into space, where they would enter gravitational orbit. The tankers would eventually be picked up by the Mars-bound crew, which would then head to a nearby fueling station to gas up before ultimately heading to Mars."

There was a paper with a very similar concept (reaching Mars via DRO) at the AAS meeting in January by Conte et al. First, the total Delta V required for a trip Earth -> LLO -> MLO is higher than Earth -> MLO. The trick is that Earth -> LLO requires less Delta V than Earth -> MLO and hence less mass has to be carried along *from Earth*. Essentially what both approaches have in common is that they say "if there's a free gas station orbiting the moon, it's cheaper to fly empty and fill up there on the way". The AAS paper actually does a decent job at estimating the "real" cost by also including estimates of the cost of a lunar base. https://pure.strath.ac.uk/portal/files/44275737/Conte_etal_AAS2015_Earth_Mars_transfers_through_Moon_distant_retrograde_orbit.pdf