Abstract
Highly nonlinear optical processes require high intensities, typically achieved with ultrashort laser pulses, and hence, they were first observed with the advent of picosecond laser technology. An alternative approach for reaching the required field intensities is offered by localized optical resonances in tailored plasmonic nanostructures, enabling the enhancement of a multitude of nonlinear phenomena. However, so far, plasmon-enhanced high-order nonlinear effects have been restricted to experiments involving short-pulsed and ultrafast laser sources. Here, we demonstrate localized three-photon photoemission from chemically synthesized plasmonic gold nanostars under continuous-wave illumination at sub-MWcm−2 incident intensities. Intensity- and polarization-dependent measurements confirm the nonlinearity of the photoemission process and agree with quantum mechanical calculations of the electron yield from nanostar tips with features smaller than 5 nm, which facilitate local intensity enhancement factors exceeding 1000. Our results open up new avenues for the design of accessible nanoscale coherent electron sources, with potential applications in microscopy, spectroscopy, sensing, and signal processing.
Highlights
Nonlinear optical processes require high intensities, typically achieved with ultrashort laser pulses, and they were first observed with the advent of picosecond laser technology
While temporal confinement is ubiquitous in the use of ultrashort laser pulses, additional spatial confinement is realized in optical nanostructures, defining the field of ultrafast nano-optics[35,36]
We demonstrated three-photon photoemission from individual gold nanoparticles using low-power CW laser radiation at a wavelength of 660 nm (1.88 eV photon energy). This type of nonlinear processes requires large light intensities typically realized by employing ultrafast laser pulses
Summary
Nonlinear optical processes require high intensities, typically achieved with ultrashort laser pulses, and they were first observed with the advent of picosecond laser technology. We study nonlinear photoelectron emission from individual resonant gold nanostars under CW excitation at incident intensities below 1 MWcm−2, using a 660-nm low-power (60 mW) laser diode.
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