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Coherent control of terahertz supercontinuum generation in ultrafast laser–gas interactions


Frequency mixing an ultrafast-pulse laser's fundamental and second-harmonic fields in semiconductors1,2, atomic gases3,4, and on metal surfaces5 generates a directional electrical current for which the magnitude and polarity depend upon the relative phase between these two fields1,2,3,4,5. As this current occurs on the timescale of the duration of the laser pulse, in the case of ultrafast lasers (<100 fs), this process can generate electromagnetic radiation at terahertz frequencies. Although such terahertz generation has been observed in semiconductors6 and air7,8,9,10,11,12,13, the terahertz generation mechanism is not well understood and the terahertz yield has not been optimized. Here, we demonstrate a coherent control scheme to optimize terahertz generation in gases, yielding a new source of high-energy (>5 µJ), super-broadband terahertz radiation (75 THz) as well as an enhanced accompanying third harmonic. We also present a unifying explanation for such extremely broad electromagnetic radiation generation.

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Figure 1: Experimental layout for B-dot probe, third harmonic and broadband THz characterization.
Figure 2: Broadband THz energy measurements with the pyroelectric detector.
Figure 3: Terahertz spectral measurements with Michelson interferometry.
Figure 4: B-dot probe measurements.
Figure 5: Anticorrelation between THz and THG.


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This work was supported through the Los Alamos National Laboratory Directed Research and Development Program for Los Alamos National Security, LLC, under the auspices of the Department of Energy, contract no. DE-AC52-06NA25396.

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A.J.T. and J.H.G. provided management oversight to this project, while K.Y.K. and G.R. planned and executed the work. K.Y.K. designed the experiment and carried out the measurements. K.Y.K. and G.R. analysed the data and performed the simulations. All authors contributed to the final manuscript.

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Correspondence to K. Y. Kim.

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Kim, K., Taylor, A., Glownia, J. et al. Coherent control of terahertz supercontinuum generation in ultrafast laser–gas interactions. Nature Photon 2, 605–609 (2008).

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