E-Mail IMAGE: At left: Experimental PASSI (photon avalanche single-beam super-resolution imaging) images of thulium-doped avalanching nanoparticles separated by 300 nanometers. At right: PASSI simulations of the same material. view more Credit: Berkeley Lab and Columbia University Since the earliest microscopes, scientists have been on a quest to build instruments with finer and finer resolution to image a cell's proteins - the tiny machines that keep cells, and us, running. But to succeed, they need to overcome the diffraction limit, a fundamental property of light that long prevented optical microscopes from bringing into focus anything smaller than half the wavelength of visible light (around 200 nanometers or billionths of a meter) - far too big to explore many of the inner-workings of a cell.