| Metadata | Details |
|---|
| Publication Date | 2020-09-28 |
| Journal | Nanophotonics |
| Authors | Qixin Shen, Amirhassan ShamsâAnsari, Andrew M. Boyce, Nathaniel C. Wilson, Tao Cai |
| Institutions | Duke University, Harvard University |
| Citations | 15 |
| Analysis | Full AI Review Included |
- Core Innovation: A metasurface platform utilizing film-coupled plasmonic nanogap cavities is demonstrated to dramatically enhance nonlinear optical processes within an ultra-thin (12 nm) diamond slab.
- Record Enhancement: Third-harmonic generation (THG) and surface second-harmonic generation (SHG) were simultaneously enhanced by 1.6 x 107-fold compared to a bare diamond reference. Four-wave mixing (FWM) showed a 3.0 x 105-fold enhancement.
- Multifunctionality: The device acts as a versatile frequency converter, simultaneously enhancing THG, SHG, sum frequency generation (SFG), and FWM by leveraging two distinct cavity modes (fundamental at 1455 nm and second-order at 840 nm).
- Mechanism: The deeply subwavelength scale of the plasmonic structures provides high electric field confinement (up to 40-fold enhancement) and relaxes stringent phase-matching requirements inherent to bulk nonlinear optics.
- Material Advantage: Diamondâs superior properties (high index, ultrawide transparency, high thermal conductivity) make it an ideal platform for integrated nonlinear devices, despite its bulk centrosymmetry (lacking bulk chi(2)).
- Target Application: The technology suggests a viable approach for on-chip conversion of color center emission (typically visible) directly into telecom wavelengths within diamond.
| Parameter | Value | Unit | Context |
|---|
| Diamond Slab Thickness (Min) | 12 | nm | Nanogap cavity region (Area A) |
| Diamond Wedge Gradient | ~2.6 | nm/”m | Sample structure |
| Gold Film Thickness (Substrate) | 75 | nm | Ground plane for nanogap cavities |
| Nanoparticle Side Length | 220 | nm | EBL-fabricated gold nanoparticles |
| Nanoparticle Pitch | 440 | nm | Array periodicity |
| THG Enhancement Factor | 1.6 x 107 | fold | Compared to bare diamond on PDMS (1455 nm pump) |
| SHG Enhancement Factor | 1.6 x 107 | fold | Compared to bare diamond on PDMS (1455 nm pump) |
| FWM Enhancement Factor | 3.0 x 105 | fold | Compared to bare diamond on PDMS |
| Max THG Conversion Efficiency | 2.33 x 10-5 | % | At 5 mW excitation power |
| Max SHG Conversion Efficiency | 7.59 x 10-6 | % | At 5 mW excitation power |
| Excitation Damage Threshold | 5 | mW | Maximum tested excitation power |
| Fundamental Cavity Resonance (Ï2) | 1455 | nm | Nanogap mode |
| Second-Order Cavity Resonance (Ï1) | 840 | nm | Nanogap mode |
| THG Output Wavelength | 485 | nm | From 1455 nm excitation |
| SFG Output Wavelength (Ï1 + Ï2) | 532 | nm | From 840 nm and 1455 nm excitation |
| FWM Output Wavelength (2Ï1 - Ï2) | 590 | nm | From 840 nm and 1455 nm excitation |
| Electric Field Enhancement (Simulated) | Up to 40 | fold | Within the 12 nm diamond gap at 1455 nm |
| FWHM Ratio (THG/SHG) | 0.78 | - | Experimental ratio (31 nm / 40 nm) |
- Nanoparticle Fabrication: Gold nanoparticles (NPs) were fabricated on a silicon substrate using Electron Beam Lithography (EBL).
- Diamond Preparation: A wedge-shaped diamond thin film was placed on a 75 nm evaporated gold ground plane, creating three distinct test areas (nanogap cavities, decoupled NPs, and diamond reference).
- Non-Disruptive Transfer: The EBL-fabricated gold NPs were transferred onto the diamond slab using a Poly-dimethylsiloxane (PDMS) stamp, ensuring the diamond itself remained unpatterned.
- Resonance Characterization: Reflection spectroscopy (700 to 1600 nm) was used to determine the fundamental (1455 nm) and second-order (840 nm) resonance modes of the nanogap cavities.
- Nonlinear Measurement (Single Pump): Power dependence measurements were performed using 1455 nm excitation (matching the fundamental mode) to confirm the cubic (THG) and quadratic (SHG) power laws and quantify enhancement factors.
- Nonlinear Measurement (Dual Pump): Two excitation wavelengths (840 nm and 1455 nm) were used simultaneously to investigate SFG and FWM.
- Time Delay Control: A variable delay stage was employed to control the relative time delay between the two excitation pulses, confirming that SFG and FWM signals peaked when the pulses perfectly overlapped (zero time delay).
- Quantum Communication: Direct frequency conversion of single-photon emission from diamond color centers (e.g., NV or SiV centers, typically visible/near-infrared) to standard telecom wavelengths (1310 nm or 1550 nm) for long-distance fiber transmission.
- Integrated Nonlinear Optics: Development of ultra-compact, on-chip frequency mixers and converters for integrated photonic circuits, leveraging diamondâs high chi(3) and thermal stability.
- High-Speed Signal Processing: Use in devices requiring simultaneous, multi-channel frequency mixing (THG, SHG, SFG, FWM) due to the relaxed phase-matching conditions in the nanogap structure.
- Advanced Sensing: Creation of highly efficient diamond-based sensors that utilize nonlinear optical readout mechanisms, benefiting from the massive field enhancement.
- Diamond Material Science: The technique provides a platform for investigating surface chi(2) effects in centrosymmetric materials like diamond, which is crucial for developing new diamond-based electro-optic devices.
View Original Abstract
Abstract Diamond has attracted great interest as an appealing material for various applications ranging from classical to quantum optics. To date, Raman lasers, single photon sources, quantum sensing and quantum communication have been demonstrated with integrated diamond devices. However, studies of the nonlinear optical properties of diamond have been limited, especially at the nanoscale. Here, a metasurface consisting of plasmonic nanogap cavities is used to enhance both Ï (2) and Ï (3) nonlinear optical processes in a wedge-shaped diamond slab with a thickness down to 12 nm. Multiple nonlinear processes were enhanced simultaneously due to the relaxation of phase-matching conditions in subwavelength plasmonic structures by matching two excitation wavelengths with the fundamental and second-order modes of the nanogap cavities. Specifically, third-harmonic generation (THG) and second-harmonic generation (SHG) are both enhanced 1.6 Ă 10 7 -fold, while four-wave mixing is enhanced 3.0 Ă 10 5 -fold compared to diamond without the metasurface. Even though diamond lacks a bulk Ï (2) due to centrosymmetry, the observed SHG arises from the surface Ï (2) of the diamond slab and is enhanced by the metasurface elements. The efficient, deeply subwavelength diamond frequency converter demonstrated in this work suggests an approach for conversion of color center emission to telecom wavelengths directly in diamond.
- 2017 - Refractory plasmonics without refractory materials [Crossref]
- 2017 - An integrated diamond Raman laser pumped in the near-visible
- 2014 - Diamond nonlinear photonics [Crossref]
- 2014 - Control of radiative processes using tunable plasmonic nanopatch antennas [Crossref]
- 2010 - Large enhancement of nonlinear optical phenomena by plasmonic nanocavity gratings [Crossref]
- 2017 - Refractory plasmonics without refractory materials [Crossref]
- 2013 - Optical Engineering of Diamond
- 2013 - Plasmonic waveguide modes of film-coupled metallic nanocubes [Crossref]
- 2018 - Comprehensive study of plasmonic materials in the visible and near-infrared: linear, refractory, and nonlinear optical properties
- 2020 - Electrical excitation and charge-state conversion of silicon vacancy color centers in single-crystal diamond membranes [Crossref]