Imaging Light with Photoelectrons on the Nano-Femto Scale by Yanan Dai

Author:Yanan Dai
Language: eng
Format: epub
ISBN: 9783030528362
Publisher: Springer International Publishing

The time- and space-dependent interference patterns provide nano–femto information on the SPP dynamics, including dispersive propagation and dephasing. To extract quantitative information on the SPP propagation in Fig. 4.9c, I plot the PEEM line profiles integrated in the region, which is indicated by a rectangle in Fig. 4.9b, as a function of delay time over a 6.4 fs range. The image shows a clear propagation of beating maxima away from the near-coupling surface as the delay is increased. The slope showing the propagation of constructive maxima is determined by the difference in the phase velocities of the SPP field and the external light. Near the coupling edge, the interference maxima oscillate back and forth because the intensity is dominated by the self-interference, which appears to oscillate due to a smaller contribution from the delay-varying cross-interference. Further from the coupling structure, however, the beating maxima are dominated by the cross-interference and therefore propagate. Such behavior is characteristic of all ITR-PEEM imaging. Tracing out the propagating beating maxima (the white dashed line in Fig. 4.9c) gives the SPPs phase velocity through the equation Vphase = Strace × c∥/(Strace + c∥), where Strace is the slope of the maxima. In the case of the hν = 2.70 eV excitation, the phase velocity is obtained to be 0.95c, which is close to the expected value of 0.94c from the dielectric function of Ag. The SPP propagation is also affected by the wave packet group velocity as well as damping, but the Ag crystal size in Fig. 4.5 is too small to propagate the SPP wave packet sufficiently far so that these effects can be accurately determined.

References

1.

Chelaru, L., et al.: Fringe fields in nonlinear photoemission microscopy. Phys. Rev. B. 73(11), 115416 (2006)ADSCrossref

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