Up/Down-Scaling Photoluminescent Micromarks Written in Diamond by Ultrashort Laser Pulses - Optical Photoluminescent and Structural Raman Imaging

At a Glance

Metadata	Details
Publication Date	2022-11-01
Journal	Micromachines
Authors	П. А. Данилов, Evgeny V. Kuzmin, Elena Rimskaya, Jiajun Chen, Р. А. Хмельницкий
Institutions	P.N. Lebedev Physical Institute of the Russian Academy of Sciences
Citations	7
Analysis	Full AI Review Included

Technical Documentation & Analysis: Up/Down-Scaling Photoluminescent Micromarks in Diamond

Executive Summary

This research demonstrates a robust method for creating scalable, non-invasive photoluminescent (PL) micromarks inside bulk diamond using ultrashort laser pulses, a technique highly relevant for high-security photonic encoding and diamond traceability.

Core Achievement: Successful up/down-scaling of micromark length, diameter, and PL contrast by varying peak laser power (0.8-2.1 MW) and exposure time (10-240 s) in the filamentary inscription regime.
Defect Engineering: The process relies on the structural modification of native nitrogen impurity centers (A, B1, H4) within the diamond lattice, generating highly luminescent NVº (Nitrogen-Vacancy) and N3 centers.
Structural Integrity: Confocal Raman analysis confirmed that the laser inscription method does not introduce structural damage to the host carbon lattice, evidenced by the constant 1332 cm^-1 Raman peak intensity.
Regime Identification: Two distinct power regimes were identified: a sub-threshold regime (P < 1.4 MW) characterized by strong NVº enhancement, and an above-threshold regime (P > 1.4 MW) leading to N3 center accumulation via photodecomposition.
Material Implication: The study utilized natural IaAB diamond with high, but variable, nitrogen content. Replication and optimization of this technology require the highly controlled purity and defect concentration offered by synthetic MPCVD Single Crystal Diamond (SCD).
Application Potential: The ability to precisely control the size and PL contrast of these marks opens new technological opportunities in diamond photonics, high-security marking, and 3D micromachining.

Technical Specifications

The following hard data points were extracted from the experimental methodology and results:

Parameter	Value	Unit	Context
Laser Wavelength (SH)	515	nm	Second Harmonic used for inscription.
Pulse Duration (τ)	0.3	ps	Ultrashort pulse regime.
Repetition Rate (f)	100	kHz	Standard inscription rate used.
Peak Laser Power (P) Range	0.8 - 2.1	MW	Used for scaling experiments.
Peak Fluence Range	2 - 5.5	J/cm²	Corresponding fluence range.
Peak Intensity Range	7 - 18	TW/cm²	High intensity required for filamentation.
Critical Power for Self-Focusing (P_cr)	≈ 0.5	MW	Threshold for filamentary inscription.
Threshold Power for N3 Increase (P_th)	≈ 1.4	MW	Separates sub- and above-threshold regimes.
Inscription Depth	≈ 300	µm	Depth inside the diamond cube.
Micromark Diameter (Spot Size)	≈ 1.8 ± 0.1	µm	1/e-intensity radius.
Initial Nitrogen Concentration [A (2N)]	≈ 230	ppm	Natural IaAB diamond sample.
NVº PL Yield Enhancement	Ten-fold	N/A	Observed in the sub-threshold regime (P < 1.4 MW).
N3 PL Yield Enhancement	Up to 40	%	Observed in the sub-threshold regime (P < 1.4 MW).
Raman Peak Intensity (1332 cm^-1)	Nearly Constant	N/A	Confirms absence of structural lattice damage.

Key Methodologies

The experiment utilized a high-precision ultrashort-pulse laser system coupled with advanced 3D confocal microscopy for inscription and characterization.

Material Selection: A colorless natural IaAB-type diamond crystal cube (4 x 4 x 4 mm³) with high aggregated nitrogen content (A-centers ~ 230 ppm) was used.
Laser Inscription System: A femtosecond Yb-doped fiber laser system (Amplitude Systemes) operating at the 515 nm second harmonic (SH) was employed.
Focusing and Depth: Laser pulses (0.3 ps, 100 kHz) were tightly focused by a 0.25 NA micro-objective lens, inscribing marks at a depth of ~300 µm inside the diamond.
Parameter Mapping: An array of micromarks was created by systematically varying the Peak Laser Power (0.8-2.1 MW) and Exposure Time (10-240 s, corresponding to 1 x 10⁶ to 24 x 10⁶ pulses).
3D Confocal Analysis: The inscribed region was characterized using 3D scanning confocal Raman/PL microspectroscopy (Renishaw inVia InSpect) with a 405 nm excitation laser.
Defect Quantification: Photoluminescence (PL) spectra were analyzed to track the formation and yield of specific color centers, including N3 (415 nm ZPL), NVº (575 nm ZPL), H3, and H4 centers.

6CCVD Solutions & Capabilities

The research successfully demonstrates the potential of laser-induced defect engineering for high-security marking. However, the use of natural diamond introduces variability in impurity concentration, limiting reproducibility. 6CCVD’s expertise in MPCVD synthetic diamond provides the necessary control and scalability to industrialize this technology.

Applicable Materials for Replication and Optimization

To achieve consistent and optimized color center yields (NVº and N3) for photonic encoding, researchers require materials with precisely controlled initial nitrogen concentrations and high crystalline purity.

Recommended Material: High-Purity Single Crystal Diamond (SCD)
- Advantage: 6CCVD’s SCD offers superior control over background impurities compared to natural IaAB diamond. We can grow SCD wafers with specific, controlled nitrogen doping levels, allowing engineers to optimize the initial concentration of A-centers (2N) or C-centers (N) necessary for efficient laser-induced vacancy aggregation and subsequent NV/N3 formation.
Scaling Material: Polycrystalline Diamond (PCD)
- Advantage: For large-scale industrial marking applications beyond small cubes, 6CCVD provides high-quality PCD plates up to 125 mm in diameter, enabling the transfer of this micromarking technology to large optical or mechanical components.

Customization Potential

6CCVD’s manufacturing capabilities directly address the dimensional and quality requirements for advanced laser processing and characterization.

Requirement from Research/Application	6CCVD Customization Capability	Benefit to Client
Custom Dimensions	Plates/wafers up to 125 mm (PCD) and custom SCD wafers.	Provides large-area substrates necessary for scaling up photonic encoding from lab-scale cubes to industrial components.
Thickness Control	SCD and PCD thickness ranging from 0.1 µm to 500 µm.	Ensures optimal material depth for bulk inscription experiments (like the 300 µm depth used here) and minimizes material waste.
Surface Quality	SCD Polishing to Ra < 1 nm; Inch-size PCD Polishing to Ra < 5 nm.	Atomic-level surface smoothness is critical for high-resolution 3D scanning confocal microscopy and minimizing spherical aberration during tight laser focusing.
Device Integration	In-house Metalization (Au, Pt, Pd, Ti, W, Cu).	Allows for the integration of marked diamond into functional devices (e.g., sensors, quantum devices) requiring electrical contacts or heat sinks.

Engineering Support

The structural transformations observed (vacancy-driven aggregation, photodecomposition) are complex defect engineering challenges.

Expert Consultation: 6CCVD’s in-house PhD team specializes in the physics and growth of diamond color centers. We offer direct engineering support to assist researchers in selecting the optimal starting material (e.g., specific nitrogen concentration) to maximize the desired color center yield (NVº or N3) for similar Diamond Photonic Encoding projects.
Global Logistics: We ensure reliable global shipping (DDU default, DDP available) for sensitive diamond materials, supporting international research efforts.

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

View Original Abstract

Elongated photoluminescent micromarks were inscribed inside a IaAB-type natural diamond in laser filamentation regime by multiple 515 nm, 0.3 ps laser pulses tightly focused by a 0.25 NA micro-objective. The micromark length, diameter and photoluminescence contrast scaled as a function of laser pulse energy and exposure, coming to a saturation. Our Raman/photoluminescence confocal microscopy studies indicate no structural diamond damage in the micromarks, shown as the absent Raman intensity variation versus laser energy and exposition along the distance from the surface to the deep mark edge. In contrast, sTable 3NV (N3)-centers demonstrate the pronounced increase (up to 40%) in their 415 nm zero-phonon line photoluminescence yield within the micromarks, and an even higher—ten-fold—increase in NV0-center photoluminescence yield. Photogeneration of carbon Frenkel “interstitial-vacancy” (I-V) pairs and partial photolytic dissociation of the predominating 2N (A)-centers were suggested to explain the enhanced appearance of 3NV- and NV-centers, apparently via vacancy aggregation with the resulting N (C)-centers or, consequently, with 2N- and N-centers.

Tech Support

Original Source

DOI: https://doi.org/10.3390/mi13111883

References

2017 - Laser writing of coherent colour centres in diamond [Crossref]
2018 - Screening and engineering of 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]
2021 - Direct writing of high-density nitrogen-vacancy centers inside diamond by femtosecond laser irradiation [Crossref]