Productivity of Concentration-Dependent Conversion of Substitutional Nitrogen Atoms into Nitrogen-Vacancy Quantum Emitters in Synthetic-Diamond by Ultrashort Laser Pulses

At a Glance

Metadata	Details
Publication Date	2023-07-09
Journal	Micromachines
Authors	S. I. Kudryashov, П. А. Данилов, Evgeny V. Kuzmin, Nikita Smirnov, Alexey Gorevoy
Institutions	Saint Petersburg Mining University, P.N. Lebedev Physical Institute of the Russian Academy of Sciences
Citations	6
Analysis	Full AI Review Included

Technical Documentation & Analysis: MPCVD Diamond for Quantum Emitter Inscription

Executive Summary

This analysis focuses on the research demonstrating the highly efficient, concentration-dependent conversion of substitutional nitrogen (C-centers) into Nitrogen-Vacancy (NV) quantum emitters using tightly focused, ultrashort laser pulses in synthetic diamond.

Core Achievement: Near-complete local conversion of C-centers (substitutional nitrogen) into NV⁰ and NV^- quantum emitters was achieved via laser-induced Frenkel (interstitial-vacancy, I-V) carbon pair generation.
Methodology: Tightly focused 515 nm, 0.3 ps femtosecond laser pulses were used in a filamentation regime to induce structural modification and defect creation in Type Ib HPHT diamond.
Material Requirement: The study relied on diamond with precisely controlled, inhomogeneous nitrogen concentrations, ranging from 22 ppm (colorless) to 70 ppm (yellow).
Quantitative Results: Estimated NV production rates (η_NV) reached 10¹²-10¹³ NV/cm³, confirming the viability of this technique for robust single-photon source fabrication.
6CCVD Value Proposition: 6CCVD specializes in high-purity, custom MPCVD diamond, offering superior control over nitrogen doping levels and homogeneity compared to the HPHT material used, enabling optimized quantum emitter density and yield for scalable quantum optics applications.
Scalability: The technique allows for 3D inscription of NV centers, which, when combined with 6CCVD’s large-area SCD and PCD wafers (up to 125mm), facilitates the mass fabrication of quantum devices.

Technical Specifications

The following hard data points were extracted from the research paper, detailing the experimental parameters and key results related to NV center inscription.

Parameter	Value	Unit	Context
Laser Wavelength (SH)	515	nm	Second Harmonic (SH) pump laser
Pulse Duration	0.3	ps	Ultrashort pulse width
Delivered Pulse Energy Range	0.09 - 0.6	µJ	Used for filamentation regime
Repetition Rate (f)	100	kHz	Fixed rate for exposure series
Spot Size (1/e-intensity radius)	0.6 ± 0.1	µm	Focused spot size
Initial N Concentration ([C_c])	22 (or 3.7 × 10¹⁸)	ppm (or cm^-3)	Colorless region (lower N)
Initial N Concentration ([C_y])	70 (or 1.2 × 10¹⁹)	ppm (or cm^-3)	Yellow region (higher N)
NV Production Rate (η_NV)	10¹² - 10¹³	NV/cm³	Estimated productivity in fs-laser regime
Saturation Time (T_sat,y)	20 - 40	s	Exposure time for complete C-center conversion in yellow region
Micromark Thickness (D)	20 - 40	µm	Typical length of laser-modified region
NV⁰ Zero-Phonon Line (ZPL)	575	nm	Neutral NV center emission
NV^- Zero-Phonon Line (ZPL)	637	nm	Negatively charged NV center emission
C-Center IR Absorption Peak	1130	cm^-1	Used for quantitative depletion measurement

Key Methodologies

The experiment utilized a precise femtosecond laser inscription technique combined with advanced spectroscopic analysis to monitor the N→NV conversion process.

Material Selection: Ib-type HPHT synthetic diamond plate (0.5 mm thickness) was chosen for its high, yet inhomogeneous, concentration of substitutional nitrogen (C-centers).
Laser Setup: A femtosecond Yb-doped fiber laser system (Satsuma) was used, operating at the 515 nm second harmonic (SH) wavelength with a 0.3 ps pulse duration.
Focusing and Inscription: Laser pulses were tightly focused using a 0.65-NA micro-objective lens, corrected for the high diamond refractive index (n ≈ 2.4), resulting in an effective NA ≈ 0.27. Inscription occurred at depths of 100-250 µm, utilizing the non-linear filamentation regime.
Exposure Matrix: Microregions were exposed in arrays, systematically varying the pulse energy (0.15-1 µJ) and exposure time (10-320 s) at a fixed 100 kHz repetition rate to study saturation kinetics.
C-Center Depletion Measurement: Differential Fourier-transform IR (FT-IR) microspectroscopy was performed to quantify the local decrease in C-center concentration, primarily monitoring the 1130 cm^-1 absorption peak.
Quantum Emitter Characterization: 3D-scanning confocal Raman and photoluminescence (PL) microspectroscopy (using 405 nm and 532 nm excitation) was employed to visualize the laser-induced N→NV transformations and measure the PL intensity saturation, corrected via the Raman signal.

6CCVD Solutions & Capabilities

This research validates femtosecond laser inscription as a leading method for creating robust NV quantum emitters. 6CCVD is uniquely positioned to supply the necessary high-specification diamond materials to advance and scale this technology.

Applicable Materials for Quantum Emitter Fabrication

The study utilized HPHT diamond, which often suffers from uncontrolled defect profiles. 6CCVD’s MPCVD growth offers superior control, essential for quantum applications.

Research Requirement	6CCVD Material Solution	Technical Advantage
Controlled Nitrogen Doping	Quantum Grade Single Crystal Diamond (SCD)	Precise, tunable nitrogen incorporation during MPCVD growth to target specific C-center concentrations (e.g., 20 ppm to 100 ppm) for optimal NV yield and charge state control (NV⁰ vs. NV^-).
High Purity Substrates	High-Purity SCD (Type IIa)	Ideal for minimizing background defects and ensuring high coherence times, crucial for single-photon source applications.
Large Area Processing	Polycrystalline Diamond (PCD) Wafers	Available up to 125 mm diameter, enabling large-scale array inscription and integration into commercial quantum devices.
Surface Quality	Ultra-Polished SCD/PCD	Polishing capability to achieve Ra < 1 nm (SCD) and Ra < 5 nm (PCD), minimizing scattering losses for optical integration.

Customization Potential for Advanced Research

The successful replication and extension of this research require materials tailored to specific laser parameters and device architectures. 6CCVD provides comprehensive customization services:

Custom Dimensions and Thickness: The paper used a 0.5 mm thick plate. 6CCVD offers SCD plates with thicknesses ranging from 0.1 µm up to 500 µm, and substrates up to 10 mm, allowing researchers to optimize the interaction depth and thermal management for high-repetition-rate laser inscription.
Precision Geometry: We provide custom laser cutting and shaping services to match unique experimental setups (e.g., the 4 mm hexagonal plate used in the study) or integrate diamond into micro-optical systems.
Metalization Services: For subsequent device integration (e.g., creating electrodes for Stark shift control or microwave delivery for spin manipulation), 6CCVD offers in-house metalization capabilities, including Au, Pt, Pd, Ti, W, and Cu deposition.

Engineering Support

6CCVD recognizes that optimizing NV creation involves complex defect engineering.

Defect Engineering Consultation: Our in-house PhD team specializes in the relationship between MPCVD growth parameters, nitrogen incorporation, and post-processing techniques (like the fs-laser inscription studied here). We can assist researchers in selecting the optimal starting material to maximize NV production rate (η_NV) and control the NV^-/NV⁰ ratio for specific quantum applications.
Material Optimization: We provide expert guidance on material specifications required for similar single-photon source fabrication and 3D quantum memory projects, ensuring the diamond substrate meets the stringent requirements for high-fidelity quantum operations.

For custom specifications or material consultation, visit 6ccvd.com or contact our engineering team directly.

View Original Abstract

Tightly focused 515-nm, 0.3-ps laser pulses modify in a laser filamentation regime the crystalline structure of an Ib-type high-pressure, high-temperature (HPHT) synthesized diamond in a thin-plate form. The modified microregions (micromarks) in the yellow and colorless crystal zones, possessing different concentrations of elementary substitutional nitrogen (N) impurity atoms (C-centers), exhibit their strongly diminished local IR absorption (upon correction to the thickness scaling factor). Simultaneously, local visible-range (400-550 nm) absorption coefficients were increased, and photoluminescence (PL) yield was strongly enhanced in the broad range of 450-800 nm. The strong yellow-red PL enhancement saturates with laser exposure, implying the complete conversion of C-centers into nitrogen-vacancy (NV0,−) ones due to the laser-induced generation of Frenkel “interstitial-vacancy” I-V carbon pairs. The other emerging blue-green (>470 nm) and green-yellow (>500 nm) PL bands were also simultaneously saturated versus the laser exposure. The observed IR/optical absorption and PL spectral changes enlighten the ultrashort pulse laser inscription of NV0−-based quantum-emitter centers in synthetic diamonds and enable the evaluation of the productivity of their inscription along with the corresponding I-V generation rates.

Tech Support

Original Source

DOI: https://doi.org/10.3390/mi14071397

References

2016 - An integrated diamond nanophotonics platform for quantum-optical networks [Crossref]
2019 - Quantum nanophotonics with group IV defects in diamond [Crossref]
2017 - Laser writing of coherent colour centres in diamond [Crossref]
2019 - Laser writing of individual nitrogen-vacancy defects in diamond with near-unity yield [Crossref]
2021 - Low-charge-noise nitrogen-vacancy centers in diamond created using laser writing with a solid-immersion lens [Crossref]
2023 - Creation of NV centers over a millimeter-sized region by intense single-shot ultrashort laser irradiation [Crossref]
2018 - Screening and engineering of colour centres in diamond [Crossref]
2022 - Signatures of ultrafast electronic and atomistic dynamics in bulk photoluminescence of CVD and natural diamonds excited by ultrashort laser pulses of variable pulsewidth [Crossref]
2021 - Direct writing of high-density nitrogen-vacancy centers inside diamond by femtosecond laser irradiation [Crossref]