Ultraviolet enhancement cavity for ultrafast nonlinear optics and high-rate multiphoton entanglement experiments


Ultrafast, ultraviolet light pulses are a key tool for spectroscopic studies (for example, molecular formation1,2 and carrier dynamics in semiconductors3) as well as a source for non-classical states of light4,5,6,7,8,9,10,11,12,13. The power required for many nonlinear processes makes amplifier systems mandatory, which significantly reduces the available repetition rate and thus often lengthens the experimental acquisition time. Here we adopt techniques recently developed for the infrared regime14,15,16 to design the first enhancement cavity for femtosecond ultraviolet pulses. An average ultraviolet power of more than 7 W at a repetition rate of 81 MHz is now available to pump a nonlinear crystal inside the cavity, applied here to implement a powerful source for high-rate experiments with entangled multiphoton states. The field enhancement enables a new scale of experiments in photonic quantum logic and in nonlinear optics research, for example, to operate optical parametric amplifiers at high repetition rates or to create high-harmonic-frequency combs14,15,16.

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Figure 1: Schematic experimental set-up.
Figure 2: UV spectra and power enhancement.
Figure 3: Count rate statistics in dependence on the average UV pump power circulating in the cavity.


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The authors acknowledge support for this work from the Deutsche Forschungsgemeinschaft Cluster of Excellence Munich-Center for Advanced Photonics (MAP), the European Union project Qubit Applications (QAP) and the Deutscher Akademischer Austausch Dienst/Ministerstwo Nauki i Szkolnictwa Wyzszego (DAAD/MNiSW). W.W. acknowledges support by the PhD program Quantum Computing, Control and Communication (QCCC) of the Elite Network of Bavaria and the Studienstiftung des deutschen Volkes.

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All authors contributed significantly to the work presented in this paper.

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Correspondence to Roland Krischek.

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Krischek, R., Wieczorek, W., Ozawa, A. et al. Ultraviolet enhancement cavity for ultrafast nonlinear optics and high-rate multiphoton entanglement experiments. Nature Photon 4, 170–173 (2010). https://doi.org/10.1038/nphoton.2009.286

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