Intense laser-Atom Physics in Scaled Interactions

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The invention of the laser in 1960 enabled a wide range of scientific and technological advances, from communications to surgery to facial recognition to analysis of Martian soil. At the heart of these innovations is the interaction of the laser light with physical objects, for example the bar code reader at the supermarket. This project will study a specific interaction of laser light with the basic building block of all matter, the atom. In this interaction, a large amount of energy from the laser light is coupled into the atom and dissipated by fragmenting the atom into secondary particles such as electrons, ions and other photons. Analyzing the composition of the fragmentation process and the energy flow among the constituents provides a microscopic view of the elementary physics. In the project, sensitive detector configurations are used to allow the measurement of the type of particle, their energy content and their emission direction in space. The program implements a detailed strategy of exploiting the scaling predicted by both classical and quantum mechanical models for exploring the global physics of the single atom response to an intense laser field. The critical scaling parameter is the color, i.e. wavelength, of the laser light and the PI shows how novel wavelength lasers can extend the breadth of experiments into an unexplored regime and thus contribute to our overall understanding of nature. Understanding this basic physics can be exploited in applications that provide direct benefits to society, such as non-invasive surgery and tomorrow’s energy sources. In addition, the laser sources developed by the research team are anticipated to have broad applications in other sectors of science and technology. Furthermore, the interdisciplinary nature of this research coupled with state-of-the-art optical engineering provide an excellent training ground for postdocs, undergraduate and graduate students. Former group members are contributing to various areas of science and technology in academia, energy and defense laboratories, and the private sector. More specifically, atoms and molecules are exposed to intense (atomic unit of field), femtosecond light pulses whose wavelength can be varied from 0.4-4 microns. At these low frequencies, the electronic response, e.g. ionization, is highly nonlinear and the field energy that quivers the electron can exceed the binding energy of the valence electron. In the experiment, the ionized electrons are angularly energy resolved and studied as a function of laser intensity, polarization and frequency. The main objectives are to map the global behavior of strong-field ionization, observe how it evolves with scaled field parameters, provide stringent tests of theory, and identify the invariant behavior in the physics. In addition, the program extends the studies into the high frequency regime, i.e. x-rays. This is accomplished by using the X-ray Free Electron Laser (XFEL) at SLAC National Laboratory. The XFEL can generate fields in the soft x-ray regime comparable to our laboratory lasers.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.