Ultrashort pulse generation by molecular modulation
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abstract
This PhD Tutorial describes a new source of coherent radiation, with a spectrum extending over many octaves of optical bandwidth. We demonstrate collinear generation of mutually coherent spectral sidebands, ranging in wavelength from 2.94 m in the infrared to 195 nm in the ultraviolet. The pulse energies are above 1 mJ/10 ns pulse for each of the nine central sidebands. The essence of our technique is the adiabatic preparation of a macroscopic molecular ensemble in a single vibrational superposition state. When this is achieved, coherent molecular motion modulates laser light and produces a wide frequency modulated (FM)-like spectrum, which allows subfemtosecond pulse compression. We use this source in two experiments: (1) we demonstrate the generation and detection of amplitude and frequency modulated light with a 90 THz modulation frequency; and (2) we demonstrate coherent control of multiphoton ionization on a few-femtosecond timescale, under conditions where photoionization requires eleven photons of the lowest frequency and five photons of the highest frequency of the spectrum. Our experiments demonstrate good mutual coherence of the generated sidebands and suggest a possibility of sub-cycle optical field shaping. This is a first step towards studying subfemtosecond atomic and molecular dynamics.
