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Spectral caustics in attosecond science


Many intriguing phenomena in nature—from phase transitions to black holes—occur at singularities. A unique type of singularity common in wave phenomena, known as caustics1,2, links processes observed in many different branches of physics3,4. Here, we investigate the role of caustics in attosecond science and in particular the physical process behind high harmonic generation5. We experimentally demonstrate spectral focusing in high harmonic generation, showing a robust intensity enhancement of an order of magnitude over a spectral width of several harmonics. This new level of control holds promises in both scientific and technological aspects of attosecond science6,7. Moreover, our study provides a deeper insight into the basic mechanism underlying the high harmonic generation process, revealing its quantum nature8 and universal properties.

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Figure 1: Singularities in the semiclassical model.
Figure 2: Experimental observation of the swallowtail caustic in HHG.


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The authors thank T. Shapira and O. Kfir for useful comments, and the Minerva Foundation, the Israeli Science Foundation and the Crown Center of Photonics for financial support. O.R. acknowledges support from the Converging Technologies Fellowship of the Israeli Ministry of Science.

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O.R. conceived the idea. O.R. and O.P. developed the theory, performed the experiments and analysed the data. All authors contributed in building the experimental set-up and writing the manuscript.

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Correspondence to O. Raz.

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The authors declare no competing financial interests.

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Raz, O., Pedatzur, O., Bruner, B. et al. Spectral caustics in attosecond science. Nature Photon 6, 170–173 (2012).

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