Generating Ultrabroadband Deep-UV Radiation and Sub-10 nm Gap by Hybrid-Morphology Gold Antennas

Abstract

We experimentally investigate the interaction between hybrid-morphology gold optical antennas and a fewcycle Ti:sapphire laser up to ablative intensities, demonstrating rich nonlinear plasmonic effects and promising applications in coherent frequency upconversion and nanofabrication technology. The two-dimensional array of hybrid antennas consists of elliptical apertures combined with bowties in its minor axis. The plasmonic resonance frequency of the bowties is red-shifted with respect to the laser central frequency and thus mainly enhances the third harmonic spectrum at long wavelengths. The gold film between two neighboring elliptical apertures forms an hourglass-shaped structure, which acts as a "plasmonic lens" and thus strongly reinforces surface currents into a small area. This enhanced surface current produces a rotating magnetic field that deeply penetrates into the substrate. At resonant frequency, the magnetic field is further intensified by the bowties. The resonant frequency of the hourglass is blueshifted with respect to the laser central frequency. Consequently, it spectacularly extends the third harmonic spectrum toward short wavelengths. The resultant third harmonic signal ranges from 230 to 300 nm, much broader than the emission from a sapphire crystal. In addition, the concentration of surface current within the neck of the hourglass antenna results in a structural modification through laser ablation, producing sub-10 nm sharp metallic gaps. Moreover, after laser illumination the optical field hotspots are imprinted around the antennas, allowing us to confirm the subwavelength enhancement of the electric near-field intensity.

Photonic Entanglement Based on Nonlinear Metamaterials

“…[ 45,46 ] With a beam spot of 150 µm diameter, the power intensity is lower than 0.1 TW cm −2 , which is still safe for metallic metamaterials to avoid damage of melting. [ 47 ]…”

Femtosecond Field‐Driven On‐Chip Unidirectional Electronic Currents in Nonadiabatic Tunneling Regime

“…Two broadband double‐chirped mirrors and a pair of fused silica wedges were employed to control the dispersion of the pulses. The pulses were characterized by dispersion‐scan method [ 33 ] and the shortest duration was retrieved to be ≃ 7.6 fs. The laser beam diameter on the sample ws estimated to be ≈7 μm, which corresponded to a simultaneous illumination of about unit cells of the nanojunctions.…”

Toroidal Metaphotonics and Metadevices

“…[147] Seeking for an intense nonlinear signal based on second or third harmonic signal generation has triggered researchers to address this fundamental necessity by developing novel optical metasurfaces. [132][133][134][135][136][137][138][139][140][141][142][143][144][145][146][147] Such particular methodology is highly important for short wavelength (e.g., UV) beam generation, [81,[148][149][150][151][152][153][154][155][156] in which traditional nonlinear crystals reach their limits in terms of transparency and phase-matching between input and output fields. [157] Among diverse second or third harmonic generation approaches, deep ( = 190-280 nm) and vacuum ( = 100-190 nm) UV (DUV and VUV) signals govern numerous vital applications, including but not limited to photochemistry, extreme subwavelength scale device fabrication, missile warning, environmental remediation, lasers, and spectroscopy.…”

“…[ 147 ] Seeking for an intense nonlinear signal based on second or third harmonic signal generation has triggered researchers to address this fundamental necessity by developing novel optical metasurfaces. [ 132–147 ] Such particular methodology is highly important for short wavelength (e.g., UV) beam generation, [ 81,148–156 ] in which traditional nonlinear crystals reach their limits in terms of transparency and phase‐matching between input and output fields. [ 157 ]…”

“…In the nonlinear optics regime, up to now, a large number of all‐dielectric and plasmonic metasurfaces have been tailored to obtain second or third harmonic signals for intensified UV light production. [ 147–153 ] Initial theoretical and experimental studies on UV sources exhibited that the generation of such shorter wavelengths, particularly in all‐dielectric and plasmonic metastructures, has its own benefits and limitations. While all‐dielectric metasurfaces take the advantage of inherent loss‐less optical response, the intensity of the induced nonlinear UV signal strongly degenerates due to the thickness of the metasurface.…”