Diamond Nitrogen-vacancy Centers and Development to Laser Science
At a Glance
Section titled âAt a Glanceâ| Metadata | Details |
|---|---|
| Publication Date | 2020-01-01 |
| Journal | The Review of Laser Engineering |
| Authors | Muneaki Hase |
| Institutions | University of Tsukuba |
| Analysis | Full AI Review Included |
Executive Summary
Section titled âExecutive SummaryâThis research investigates the impact of Nitrogen-Vacancy (NV) centers on the nonlinear optical properties of diamond using ultrafast femtosecond laser pulses, aiming to advance high-speed quantum sensing technologies.
- Core Achievement: The introduction of NV centers significantly enhances both the Optical Kerr Effect (OKE) and Two-Photon Absorption (TPA) in diamond crystals.
- Nonlinearity Enhancement: The nonlinear refractive index (|n2|) was dramatically increased by over 30 times (from 0.73 x 10-20 m2/W to 24.2 x 10-20 m2/W) in heavily implanted samples compared to pure diamond.
- Mechanism: The strong enhancement of the OKE signal in high-density NV samples is hypothesized to originate from a cascading OKE process, where the high concentration of NV centers breaks the spatial inversion symmetry near the diamond surface.
- Performance Metric: The nonlinear Figure of Merit (FOM = 2βΝ/n2) reached approximately 4.7 in the high-dose NV diamond, a value comparable to amorphous silicon (FOM â 3.0), indicating potential for integrated nonlinear optical devices.
- Application Potential: Since nonlinear optical effects occur on the femtosecond timescale, this technology opens the door for high-speed, time-resolved quantum sensing (e.g., electro-optic effects) not achievable with conventional methods.
- Methodology: Experiments utilized Z-scan (closed aperture) and time-resolved pump-probe reflectivity measurements with 800 nm femtosecond lasers.
Technical Specifications
Section titled âTechnical Specificationsâ| Parameter | Value | Unit | Context |
|---|---|---|---|
| Diamond Band Gap (Room Temp) | 5.5 | eV | Insulating property |
| NV Center Energy Gap (3A2 to 3E) | 1.945 | eV | Triplet ground to excited state transition |
| NV Excitation Wavelength | 532 | nm | Green laser (for PL readout) |
| NV Emission Wavelength (ZPL) | 637 | nm | Zero Phonon Line (Red PL) |
| NV Spin Coherence Time (T1, Bare) | 5.1 Âą 0.3 | ms | Baseline for quantum sensing |
| Laser Center Wavelength | 800 | nm | Used for OKE/TPA measurements |
| Laser Pulse Width | 40 | fs | Used for nonlinear optics study |
| Laser Repetition Rate | 100 | kHz | Used for Z-scan and Pump-Probe |
| N+ Implantation Dose (High) | 1.0 x 1012 | N+/cm2 | Heavily doped sample (Sample 3) |
| N+ Implantation Depth (30 keV) | ~50 | nm | Calculated depth from surface |
| Nonlinear Refractive Index ( | n2 | , Undoped) | 0.73 x 10-20 |
| Nonlinear Refractive Index ( | n2 | , High Dose) | 24.2 x 10-20 |
| Two-Photon Absorption (β, High Dose) | 1.01 x 10-1 | cm/GW | TPA coefficient (Sample 3) |
| Nonlinear Figure of Merit (FOM) | ~4.7 | N/A | High-dose sample (2βΝ/n2) |
Key Methodologies
Section titled âKey MethodologiesâThe study employed two primary methods for NV center creation and two advanced optical techniques for characterization:
NV Center Creation Methods
Section titled âNV Center Creation Methodsâ-
Ion Implantation and Annealing (Standard Method):
- High-purity CVD diamond crystals were implanted with Nitrogen ions (N+).
- Typical acceleration voltage for N+ was 30 keV, resulting in NV centers distributed approximately 50 nm deep from the surface.
- Implantation doses ranged from 1011 to 1012 N+/cm2.
- Subsequent high-temperature annealing was performed to mobilize vacancies (V) which then trap the implanted N atoms to form the NV structure (N-V).
-
Femtosecond Laser Irradiation (Alternative Method):
- NV centers can also be created using near-infrared femtosecond pulses (790 nm wavelength, 250 fs pulse width, 1 kHz repetition rate).
- This method allows for simultaneous NV creation and laser annealing, eliminating the need for subsequent thermal processing.
- NV centers created this way are distributed up to 200 nm deep.
Nonlinear Optical Characterization
Section titled âNonlinear Optical Characterizationâ-
Z-scan (Closed Aperture Mode):
- Purpose: To measure the nonlinear refractive index (n2) and the two-photon absorption coefficient (β).
- Setup: Utilized a regenerative amplifier producing 800 nm, 40 fs pulses at 100 kHz repetition rate.
- Procedure: The diamond sample was scanned along the optical axis (Z-axis) through the focus of a Gaussian beam. The change in transmitted light intensity through a closed aperture was measured to determine the phase shift (âĎ0) and loss (âĎ0), which relate directly to n2 and β.
-
Time-Resolved Pump-Probe Reflectivity:
- Purpose: To measure the dynamics of reflectivity changes (âR/R) caused by free carrier generation and relaxation.
- Setup: Used the same 800 nm femtosecond laser system.
- Procedure: A strong pump pulse excites the sample, and a time-delayed probe pulse measures the resulting change in reflectivity. This technique provides high temporal resolution, allowing observation of processes like free carrier generation via two-photon excitation into the conduction band.
Commercial Applications
Section titled âCommercial ApplicationsâThe enhanced nonlinear optical properties of NV-doped diamond, combined with the inherent robustness and quantum capabilities of the NV center, suggest applications in several high-tech sectors:
- Quantum Sensing: Development of ultra-high-speed, time-resolved sensors for electric and magnetic fields, leveraging the femtosecond response time of the nonlinear effects (Electro-Optic Kerr Effect).
- Ultrafast Photonics: Creation of compact, high-speed optical switches, modulators, and logic gates, utilizing the large nonlinear refractive index (|n2|) for all-optical signal processing.
- Integrated Quantum Devices: Integration of NV-based quantum sensors onto standard semiconductor platforms (e.g., p-i-n diodes) for scalable quantum technology and sensing chips.
- Quantum Computing: NV centers serve as robust, room-temperature qubits, and the enhanced optical control mechanisms could improve readout and entanglement operations.
- High-Resolution Imaging: Advanced nuclear magnetic resonance (NMR) imaging and spectroscopy, particularly for imaging active species in biological or chemical systems, utilizing the NV centerâs spin properties.
View Original Abstract
Nitrogen-vacancy (NV) center in diamond crystals offers high spatial-resolution quantum sensing based on controllable photo-luminescence under microwave irradiation. In order to explore possible development of NV centers toward nonlinear quantum sensing, we investigate the effect of NV centers in single crystal diamond on nonlinear optical effects using 40 fs femtosecond laser pulses. The near-infrared femtosecond pulses allow us to study purely nonlinear optical effects, such as optical Kerr effect (OKE) and two-photon absorption (TPA). We found that both nonlinear optical effects are significantly enhanced by the introduction of NV centers. In particular, our data demonstrate that the OKE signal is strongly enhanced for the heavily implanted type-IIa diamond, being possibly originated from cascading OKE, where the high-density NV centers break the spatial inversion symmetry near the surface region of diamond.