Intense Laser-Atom Physics in Scaled Interactions

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The fundamental interaction of laser light with matter provides the foundation of modern basic and applied optical research. The impact on basic research was exemplified by the recent detection of gravitational waves emitted by colliding black holes, which confirmed Einstein's theory of gravity. At the heart of this achievement is an optical interferometer detector. In general, interferometers have exquisite sensitivity for detecting small disturbances, be they gravitational waves propagating through space or the minute motion of an electron in an atom as explored in this project. The interaction of light and matter is also being exploited in applications that provide more tangible benefits to society, such as non-invasive surgery and future sources of energy. In these cases, the ability to direct large amounts of laser energy into matter in a precise and controllable manner is paramount. Understanding the physics responsible for precisely sculpting the laser-matter interaction is a major thrust of this project. When a large amount of laser light is coupled into matter, the energy is dissipated by fragmenting the matter, releasing secondary particles such as electrons, ions, and photons. Analyzing the composition of the fragmentation process and the energy flow among the constituents provides a microscopic view of the elementary physics. In this project, sensitive detector configurations are used to allow the measurement of the type of particles, their energy content, and their emission direction, taking into account interference. This program implements a detailed strategy of utilizing the scaling predicted by semi-classical and quantum models for exploring the global physics of a single atom response to an intense electromagnetic field. The critical scaling parameter is the color, i.e. frequency, of the laser light and the project outlines how novel wavelength lasers can extend the breadth of experiments into an unexplored regime and thus contribute to our overall understanding of nature. 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 μm. 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 resolved in angle and energy, 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 laser sources developed by this program have broad applications in science and technology. The interdisciplinary nature of this research coupled with state-of-the-art optical engineering provide an excellent training ground for both 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.