Crystal-based molecular modulation for arbitrary spatio-temporal optical waveform synthesis
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abstract
A technique is being developed for sub-femtosecond pulse generation and sub-cycle pulse shaping. The essence of the technique is the preparation of a macroscopic medium in a coherent superposition-state. This preparation is accomplished by two laser pulses tuned close to a molecular Raman resonance. The resultant molecular motion modulates the input light to produce a wide spectrum of discrete sidebands. Broadband coherent generation in Raman-active crystals is shown, and the capability to control spectral phases of the Raman sidebands in a precise and stable manner is demonstrated. This is the first step toward sub-cycle pulse shaping, which will allow synthesis of waveforms where the electric field is an arbitrary predetermined function of time, not limited to quasi-sinusoidal oscillations. As a result, a direct and precise control of electron trajectories in photoionization and high-order harmonic generation will become possible. In addition, coherent transfer of optical orbital angular momentum in multi-order Raman generation is investigated. The use of singular light beams, such as optical vortices, provides a new degree of freedom for ultrashort pulse manipulation, and will open a possibility for spatio-temporal engineering of sub-cycle pulses.The broad impact of this research derives not only from the promised discoveries in fundamental science, but also come from a variety of practical applications of the new broad-band Raman source. These applications are: optical coherence tomography, ultrafast spectroscopy, precision metrology, to name a few. In addition, the technique of molecular modulation can be used to generate coherent radiation in the UV and IR spectral regions, where laser sources are not readily available. Eventually, applications to lithography, chemistry, biology, and astronomy may become practical. An important part of this project is the education and training of graduate and undergraduate students. The project provides these students with training in the field of quantum optics and laser physics and will allow them to develop both theoretical and experimental skills which are in high demand.
