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High-harmonic generation by resonant plasmon field enhancement


High-harmonic generation by focusing a femtosecond laser onto a gas is a well-known method of producing coherent extreme-ultraviolet (EUV) light1,2,3. This nonlinear conversion process requires high pulse intensities, greater than 1013 W cm-2, which are not directly attainable using only the output power of a femtosecond oscillator. Chirped-pulse amplification enables the pulse intensity to exceed this threshold by incorporating several regenerative and/or multi-pass amplifier cavities in tandem4,5. Intracavity pulse amplification (designed not to reduce the pulse repetition rate) also requires a long cavity6,7. Here we demonstrate a method of high-harmonic generation that requires no extra cavities. This is achieved by exploiting the local field enhancement induced by resonant plasmons within a metallic nanostructure consisting of bow-tie-shaped gold elements on a sapphire substrate. In our experiment, the output beam emitted from a modest femtosecond oscillator (100-kW peak power, 1.3-nJ pulse energy and 10-fs pulse duration) is directly focused onto the nanostructure with a pulse intensity of only 1011 W cm-2. The enhancement factor exceeds 20 dB, which is sufficient to produce EUV wavelengths down to 47 nm by injection with an argon gas jet. The method could form the basis for constructing laptop-sized EUV light sources for advanced lithography and high-resolution imaging applications.

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Figure 1: Apparatus for high-harmonic generation by electric field enhancement using a nanostructure of bow-tie elements.
Figure 2: Finite-difference time-domain simulation of local field enhancement.
Figure 3: Scanning electron microscope image of the nanostructure used for high-harmonic generation.
Figure 4: Measured spectrum of generated high harmonics.


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This work was supported by the Creative Research Initiatives Program of the Ministry of Science and Technology in the Republic of Korea.

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Correspondence to Seung-Woo Kim.

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Kim, S., Jin, J., Kim, YJ. et al. High-harmonic generation by resonant plasmon field enhancement. Nature 453, 757–760 (2008).

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