Temporal Control of Light Echoes

Scientists at Paderborn University, the Technical Univer­sity of Dortmund and the University of Würzburg have for the very first time succeeded in using laser pulses to precisely control photon echoes, which can occur when light waves super­impose on each other.

Illustration for the first specifical control of a photon echo using laser pulses. (Source: B. Mazhiqi, U. Paderborn)

“Just imagine that you could tailor when you wanted the echo to come back to you,” says Torsten Meier from Pader­born University. A team of scientists has now achieved just this. Not for acoustic signals, however, but for optical signals: The scientists succeeded in controlling photon echoes emitted by semi­conductor quantum dots with sub-second precision. Meier explains: “Optical echoes are somewhat different to conven­tional acoustic echoes, because they are not generated by the reflection of waves, but rather in a non­linear optical process. Two short laser pulses are sent to a sample: The first represents the signal and the second the forest. This provides for the reflection. When the lag time of these pulses is doubled, a new light pulse, the photon echo, is emitted by the system exposed to the light.”

Using a further control pulse, the researchers were able to control this photon echo within the picoseconds range, and thereby delay it to a desired point in time. Such control is particularly pertinent for nano­photonic circuits in which multiple optical systems need to be precisely synchronised with each other. The theo­retical prediction of the effect was developed in Torsten Meier’s research group. A big challenge was the experimental implementation, which was carried out in the research group led by Ilya Akimov (Technical University of Dortmund).

“The temporal control of optical echoes is a highly dynamic effect, whereby the control pulse virtually pauses the system,” says Hendrik Rose, a PhD student in Paderborn. Alexander Kosarev, a PhD student at the Technical Univer­sity of Dortmund, adds: “This effect was recently theoretically predicted, was success­fully experi­mentally implemented by us and offers a wealth of possibilities for mani­pulating light emissions from semi­conductor systems.” The samples used were produced in Sven Höfling’s (University of Würzburg) research group. (Source: U. Paderborn)

Reference: A. N. Kosarev et al.: Accurate photon echo timing by optical freezing of exciton dephasing and rephasing in quantum dots, Comm. Phys. 3, 228 (2020); DOI: 10.1038/s42005-020-00491-2

Link: Computational Optoelectronics and Photonics (T. Meier), University of Paderborn, Paderborn, Germany

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