Since the original invention of the laser nearly half a century ago, laser physics has evolved on two seemingly divergent paths. High power lasers with short pulses and broad spectral bandwidths were developed for use studying atomic and molecular dynamics and continuous lasers with very narrow bandwidths were developed and used in high-resolution spectroscopy. The frequency comb technique - invented by Hall and Hansch and recognized by the 2005 Physics Nobel prize - brought the paths back together and opened new opportunities for precision spectroscopy and dynamics experiments, the theme of this project. The frequency-comb technique allows production of laser pulses that consist of only a few optical cycles with the phase being precisely controlled, or equivalently a set of closely spaced colors with precisely defined frequency. The technique enables control of the temporal evolution of the laser field with sub-cycle precision thus giving access to the attosecond time domain. The attosecond (a billionth of a billionth of a second) time domain is the natural time scale of electron motion in atoms and molecules. Therefore, attosecond illumination makes it possible to take snapshots of electron dynamics, e.g. in chemical reactions. Only very recently has it become possible to generate attosecond laser pulses, a development of fundamental importance for atomic and molecular physics, for chemistry and for biology.

This project will develop a versatile phase-coherent laser system that will enable research and education in attosecond laser physics at Texas A&M University. The core of this system will consist of a high-power chirped-pulse optical parametric amplifier capable of generating phase-stabilized few-cycle pulses in the infrared (IR) spectral region. Such pulses will serve as probes in strong-field laser physics experiments. Furthermore, they will allow production of isolated attosecond pulses of extreme ultraviolet (XUV) radiation which are perfectly synchronized with the driving optical field. Simultaneous availability of phase-stabilized few-cycle IR pulses and synchronized XUV pulses will provide capabilities for exploring the attosecond dynamics of molecular dissociation and molecular alignment. In addition, various ideas exploiting unique properties of molecules vibrating and rotating in lockstep will be tested. The system will serve as a valuable resource to a large number of Texas A&M science and engineering faculty and students.

The project will offer excellent training opportunities to graduate and undergraduate students, and will train the workforce necessary for the countless applications of phase-coherent laser systems, XUV technology, and ultra-fast optics in general. The planned collaborations with leading scientists in the US and Europe will provide the students with valuable international experience. The results of this project will be disseminated through scientific publications, colloquia, and conference presentations by faculty and students. Outreach activities such as summer schools, lecture series, science-themed days will be used to promote the project, attract the best students, and inform the interested public.

Project Report

We have developed a versatile phase coherent laser system with stabilized carrier-envelope phase for attosecond laser physics and for precision spectroscopy. The laser system enabled a significant number of faculty and students to perform research and education in some of the most promising fields of atomic, molecular, and optical physics, physical chemistry, laser material processing, and nano technology. Among these we performed studies on strong-field laser physics, ionization and fragmentation of atoms and molecules, coherent control of their interaction with ultrashort laser pulses. The spectrum of the generated light was extended to the extreme ultra-violet spectral region with high harmonic generation process in gases. The enhancement of the high harmonic output at short wavelengths was explored with approaches based on pulse shaping and gas mixtures. The involvement of graduate and undergraduate students in the development of the system was of central importance and contributed to training of the workforce necessary for further progress in ultrafast photonics and extreme ultraviolet radiation. The project took advantage of ongoing collaborations with leading scientists in the US and Europe, which also helped to provide our students with valuable international experience. During the duration of the project two students performed their research for the PhD and three obtained Masters degrees. In addition several undergraduate students received training through the research experience for undergraduate students (REU) program. The project resulted in thirteen journal publications, and the results were also presented at the national and international conferences.

National Science Foundation (NSF)
Division of Physics (PHY)
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Kathleen V. McCloud
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Texas A&M Research Foundation
College Station
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