Quantum optical networks will enable distribution of quantum entanglement at long distances, with applications including interconnects between future quantum computers and secure quantum communications. I will present our recent work on developing quantum networking components based on rare-earth ions such as single optically addressable quantum bits based on ytterbium 171 in yttrium orthovanadate, microwave to optical transducers based on erbium doped crystals coupled to microwave and optical resonators, and on-chip telecom optical quantum memories.
Ultrashort extreme-ultraviolet (EUV) light pulses are an important tool for time-resolved pump-probe spectroscopy to
investigate the ultrafast dynamics of electrons in atoms and molecules. Among several methods available to generate
ultrashort EUV light pulses, the nonlinear frequency upconversion process of high-harmonic generation (HHG) draws
attention as it is capable of producing coherent EUV pulses with precise control of burst timing with respect to the
driving near-infrared (NIR) femtosecond laser. In this report, we present and discuss our recent experimental data
obtained by the plasmon-driven HHG method that generate EUV radiation by means of plasmonic nano-focusing of NIR
femtosecond pulses. For experiment, metallic waveguides having a tapered hole of funnel shape inside were fabricated
by adopting the focused-ion-beam process on a micro-cantilever substrate. The plasmonic field formed within the funnelwaveguides
being coupled with the incident femtosecond pulse permitted intensity enhancement by a factor of ~350,
which creates a hot spot of sub-wavelength size with intensities strong enough for HHG. Experimental results showed
that with injection of noble gases into the funnel-waveguides, EUV radiation is generated up to wavelengths of 32 nm
and 29.6 nm from Ar and Ne gas atoms, respectively. Further, it was observed that lower-order EUV harmonics are cut
off in the HHG spectra by the tiny exit aperture of the funnel-waveguide.
High-harmonic generation to produce ultrashort EUV pulses by frequency-upconversion of near-infrared (NIR) pulses
requires strong laser intensities. Here we describe a 3-dimensional metallic waveguide that enables plasmonic generation
of ultrashort EUV pulses through field enhancement by means of surface-plasmon polaritons. Details on the design and
fabrication of the plasmonic waveguide on the tip of a cantilever nanostructure are explained along with discussions on
experimental data.
We discuss how the intriguing phenomenon of surface plasmon resonance (SPR) can be exploited in enhancing the
intensity field of the incident femtosecond laser for the purpose of high harmonic generation (HHG). We first summarize
our previous attempt made with a 2-D planar nanostructure comprised of metallic bow-tie nano-antennas, which enabled
us to generate up to 21st harmonics from Xenon gas using 1-nJ pulse energy with an intensity enhancement factor of ~20
dB. Then we describe another attempt currently being made by devising a 3-D nano-waveguide with the aim of
improving the HHG conversion efficiency by expanding the localized volume of field enhancement by means of
propagating surface plasmon polaritons (SPPs). Our finite-difference time-domain (FDTD) calculation shows that the
enhanced volume can be increased significantly by optimal selection of the waveguide's geometrical parameters as
verified in our preliminary experimental results.
When a metallic nanostructure is illuminated by ultrashort light pulses, the excitation of surface plasmons is observed
along with subsequent strong enhancement of the electric field in the vicinity of the nanostructure. This localized surface
plasmonic resonance is exploited to generate coherent extreme ultraviolet light and soft-X ray by interacting noble gas
atoms with femtosecond laser pulses. The resulting field enhancement is much affected by the 3-D shape of the used
nanostructure, so various nanostructure shapes are examined through finite-difference time-domain analysis to predict
their performance in high harmonic generation.
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