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

Executive Summary

Core Achievement: Demonstrated precise up/down-scaling of photoluminescent (PL) micromarks inscribed deep within natural IaAB diamond using 515 nm, 0.3 ps ultrashort laser pulses in the filamentation regime.
Non-Invasive Encoding: The inscription process causes structural modification of nitrogen impurity centers (color centers) but does not induce detectable damage to the host carbon lattice, confirmed by constant 1332 cm^-1 Raman intensity.
Scaling Behavior: Micromark length, diameter, and PL contrast scale predictably with increasing peak laser power (P) and exposure time (T), eventually reaching saturation due to the intensity clamping effect of filamentation.
Color Center Modification: The process significantly enhances the PL yield of key color centers: N3 (3NV) centers increase up to 40%, and NV⁰ centers show an even higher, ten-fold increase.
Power Regimes Identified: Two distinct atomistic transformation regimes exist:
1. Sub-threshold (P < 1.4 MW): Dominated by vacancy-driven aggregation, enhancing NV-center emission.
2. Above-threshold (P > 1.4 MW): Dominated by photodecomposition of initial A- (2N) and H4-centers, resulting in stable terminal N3-centers.
Technological Impact: This method provides a robust, non-thermal pathway for 3D photonic encoding and structural modification in high-nitrogen natural diamonds, opening opportunities for advanced diamond photonics and micromachining.

Technical Specifications

Parameter	Value	Unit	Context
Laser Wavelength (SH)	515	nm	Inscription source
Pulse Duration (τ)	~0.3	ps	Ultrashort pulse regime
Repetition Rate (f)	100	kHz	Standard inscription rate (0-500 kHz variable)
Focusing Objective	0.25	NA	Micro-objective lens
Effective NA	0.1	-	Due to diamond refractive index (n ≈ 2.4)
Spot Size (w₀)	1.8 ± 0.1	µm	1/e-intensity radius
Inscription Depth	~300	µm	Inside the diamond bulk
Peak Power Range (P)	0.80 - 2.13	MW	Used for micromark array inscription
Peak Fluence Range	2 - 5.5	J/cm²	Corresponding to peak power range
Peak Intensity Range	7 - 18	TW/cm²	Corresponding to peak power range
Exposure Time (T)	10 - 240	s	Corresponds to 1 x 10⁶ to 24 x 10⁶ pulses
Critical Power (P_cr)	≈ 0.5	MW	Threshold for self-focusing/filamentation
Diamond Type	Natural IaAB	-	Colorless crystal cube (4 x 4 x 4 mm³)
Nitrogen (A-centers)	~230	ppm	Initial impurity concentration
Nitrogen (B1-centers)	~50	ppm	Initial impurity concentration
Characterization Wavelength	405	nm	Confocal Raman/PL excitation source
N3 Center ZPL	415	nm	Zero-Phonon Line (ZPL)
Diamond Raman Peak	1332	cm^-1	Triply degenerate optical phonon

Key Methodologies

The experiment utilized a combination of ultrashort pulse laser inscription in the filamentation regime followed by 3D scanning confocal microspectroscopy for comprehensive characterization.

Laser Inscription Setup:
- A Satsuma femtosecond Yb-doped fiber laser system (operating at 1030 nm) was frequency-doubled to 515 nm (SH).
- Pulses (0.3 ps duration, 100 kHz repetition rate) were focused into the diamond bulk (~300 µm depth) using a 0.25 NA micro-objective.
- The sample (natural IaAB diamond) was mounted on a PC-driven 3D motorized translation stage (TS).
Micromark Array Generation:
- An array of micromarks was inscribed by varying two primary parameters: Peak Laser Power (P: 0.80 MW to 2.13 MW) and Exposure Time (T: 10 s to 240 s).
- Inscription occurred in the filamentary regime (P > P_cr ≈ 0.5 MW), ensuring extended, homogeneous energy deposition along the track.
Impurity Characterization (FT-IR):
- The initial nitrogen impurity concentrations (A, B1, B2 centers) of the IaAB diamond were determined using Fourier-Transform Infrared (FT-IR) spectroscopy (Bruker Vertex V-70).
3D Confocal Microspectroscopy:
- The inscribed region was characterized using 3D scanning confocal Raman/PL microspectroscopy (Renishaw inVia InSpect) at room temperature.
- Excitation was performed at 405 nm.
- Raman Imaging: Used to monitor structural damage by tracking the intensity of the 1332 cm^-1 diamond optical phonon peak.
- PL Imaging (Green-Red): Used to measure micromark length, diameter, and overall PL contrast (550 nm wavelength).
- PL Imaging (Specific Centers): Used to quantify the modification of specific color centers: N3 (3NV) at 415 nm ZPL and NV⁰ at 575 nm ZPL.
Data Analysis:
- Micromark characteristics (length, diameter, normalized PL intensity) were plotted as a function of peak power and exposure time to analyze scaling and saturation effects.
- Normalized PL intensity spectra (micromark/reference) were used to identify the specific color center transformations occurring in the sub-threshold and above-threshold power regimes.

Commercial Applications

This technology enables high-security, non-invasive encoding and precise material modification, primarily targeting high-value materials and advanced photonic devices.

Industry/Sector	Application/Product	Technical Benefit
High-Value Goods/Jewelry	Non-invasive photonic encoding and trademarking of natural diamonds.	Provides permanent, sub-surface, high-contrast marks without compromising structural integrity (no Raman damage).
Quantum Technology	Creation of stable, high-density arrays of nitrogen-vacancy (NV) and N3 centers for quantum computing and sensing.	Allows precise 3D placement and control over color center type (NV⁰ vs. N3) by tuning laser power.
Diamond Photonics	Fabrication of integrated photonic circuits, waveguides, and resonators within bulk diamond.	Utilizes the filamentation regime for extended, homogeneous modification tracks deep inside the material.
Micromachining	High-precision 3D structural modification and material processing in ultra-hard, transparent dielectrics.	Offers predictable up/down-scaling of modification features (length and diameter) based on input laser parameters.
Materials Science Research	Controlled study of laser-induced atomistic transformations and defect engineering in wide bandgap semiconductors.	Provides a method to distinguish between vacancy-driven aggregation and photolytic dissociation mechanisms in nitrogen-rich diamond.

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]