INSPIRE: Compact X-Ray Laser in "Water Window" and Microscopy of Cell Membranes

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The ultimate goal of this multidisciplinary INSPIRE award is to enable a new, very high resolution microscope which is able to see inside biological cells by using light which is more energetic than ordinary visible light, but not as energetic as the light used in conventional medical x-rays. In specific, this project seeks to produce and use "soft x-ray" light that will travel between 3 and 4 billionths of a meter during each oscillation of the light (wavelengths 3.4 and 4.0 nm). These wavelengths fall in the so-called "water window" (2.3-4.4 nm) in which water is transparent, but many other parts of cells are not. Using light with these wavelengths allows one to see through the water inside cells to clearly visualize the functional parts of the cells in high resolution. The key enabling tool is called an X-ray laser (XRL), and this project seeks to produce one that is sufficiently small and affordable that it can be put into widespread use to image live biological cells in their natural environment. The work is based on the use of highly charged ions, atoms which have most of their electrons removed. Included in this project is the goal of demonstrating the utility of the new XRL by imaging natural cell membranes. This work is co-funded by the NSF Office of Integrative Activities, the Atomic, Molecular, and Optical Experimental Physics Program, the NSF/DOE Partnership in Basic Plasma Science and Engineering, the Instrument Development for Biological Research Program, and the Emerging Frontiers Office of the Biology Directorate.Recently, high gain was demonstrated for the first time in a recombination X-ray laser at 4.0nm This result stimulated a new idea to efficiently generate attosecond pulses by utilizing an XRL at 4.0 nm in combination with an infrared (IR) field directly in the inverted media of a recombination XRL. This idea was developed theoretically at Texas A&M University (TAMU) based on quantum optics and is proposed here to test this idea experimentally at Princeton as part of this INSPIRE project. It is expected that the practical application of an XRL for biological imaging requires the laser pulses to have an energy of 2 - 4 micro-Joules of energy per pulse. Therefore the crucial issue for this project will be the search for large XRL beam intensity amplification. The natural extension of this search will be the generation of high XRL beam intensity at another water window wavelength, in this case 3.4nm. By using a Schwarzschild multilayer coated objective and a high sensitivity two dimensional charge-coupled device detector, the cell radiation exposure will be kept low to allow the imaging of live cells.