Detecting Spin Currents in Ballistic Nanostructures J. A. Folk1,2, R.M. Potok2, C. M. Marcus2 1 Department of Physics, Stanford University, 2Department of Physics, Harvard University Many recent experiments have probed the spin transport properties of mesoscopic structures such as quantum point contacts and quantum dots. They have been motivated both by a desire to understand the fundamental spin physics of these few-electron systems where coherence and interactions both play critical roles, and by the possibility of using them as spin manipulation devices for spintronics and quantum information processing applications. One difficulty with most of these experiments is that they attempt to decipher spin effects from, for example, the effects of an in-plane magnetic field on transport measurements or even-odd correlations in an energy level structure, sometimes making interpretation of the results unclear. In this talk, we present a new technique to measure the spin-polarization of currents from mesoscopic devices directly, using a small perpendicular magnetic field to bend and focus the ballistic electron trajectories of current from the device under test into a spin selective collector (a quantum point contact in a large in-plane field) in the standard transverse electron focusing geometry. We have tested the technique using the relatively well-understood spin properties of quantum point contacts in a large in-plane magnetic field, and are at present applying it to spin measurements of both open and nearly-isolated quantum dots. The talk will also include a comparison of these experiments to previous spin measurements of dots and point contacts that have been performed in this lab and others.