Interactions of Atomistic Nitrogen Optical Centers during Bulk Femtosecond Laser Micromarking of Natural Diamond

At a Glance

Metadata	Details
Publication Date	2023-01-29
Journal	Photonics
Authors	Elena Rimskaya, G. Yu. Kriulina, Evgeny V. Kuzmin, S. I. Kudryashov, П. А. Данилов
Institutions	Lomonosov Moscow State University, P.N. Lebedev Physical Institute of the Russian Academy of Sciences
Citations	4
Analysis	Full AI Review Included

Executive Summary

This research details the controlled transformation of nitrogen impurity centers in bulk natural IaAB-type diamond using femtosecond (fs) laser direct writing, a critical step for developing 3D photonic devices.

Core Achievement: Demonstrated precise, depth-resolved control over the aggregation state of nitrogen optical centers (N-centers) within the bulk diamond using 515 nm, 300 fs laser pulses.
Mechanism Identification: The process involves vacancy-mediated dissociation of highly aggregated B1 and B2 centers, leading to the formation of lower-aggregated centers (H3, H4, NV⁰, NV^-).
Energy Dependence: Low pulse energies promote dissociation into H3 and H4 centers (intermediate products). High pulse energies drive further dissociation and conversion into stable NV centers (NV⁰, NV^-).
Exposure Control: Micromark brightness (PL intensity) is strongly dependent on exposure time, showing a saturation plateau after approximately 60 seconds of irradiation, indicating a high-yield, stable NV formation process.
Technological Impact: The ability to spectrally contrast and control the formation of NV centers deep within the diamond bulk opens new avenues for three-dimensional micro-electrooptical and photonic device fabrication.

Technical Specifications

Parameter	Value	Unit	Context
Diamond Type	Natural IaAB	N/A	High-nitrogen octahedral crystal
Initial A-Center [A(2N)]	~175	ppm	Initial impurity concentration
Initial B1-Center [B1(4NV)]	~360	ppm	Initial impurity concentration
Inscription Laser Wavelength	515	nm	Visible range fs-laser
Pulse Duration	300	fs	Ultrashort pulse regime
Repetition Rate	100	kHz	Laser operation frequency
Focusing Objective NA	0.25	N/A	Low NA micro-objective
Inscription Depth (z)	~125	µm	Focal plane depth inside diamond
Pulse Energy Range	0.1 - 1.6	µJ	Variable marking parameter
Exposure Time Range	10 - 240	s	Corresponds to 1M to 24M pulses
PL Excitation Wavelengths	405, 532	nm	Characterization method
NV^- Zero Phonon Line (ZPL)	637	nm	Characteristic PL peak
NV Band Maximum	660	nm	Wide NV band peak (405 nm excitation)
H-Band Maximum	550	nm	Wide H-band peak (405 nm excitation)
NV Formation Saturation	~60	s	Exposure time threshold for maximum PL brightness

Key Methodologies

The experiment utilized a multi-shot, direct laser writing approach followed by 3D confocal photoluminescence (PL) microspectroscopy for characterization.

Material Characterization: Initial nitrogen aggregation states (A, B1, B2 centers) were quantified using Fourier-Transform Infrared (FT-IR) spectroscopy and optical transmission spectroscopy.
Laser Inscription Setup: A Satsuma fs-laser workstation delivered 515 nm, 300 fs pulses, focused by a 0.25 NA micro-objective into the diamond bulk at a nominal depth of 125 µm.
Micromark Array Formation: Arrays were inscribed by varying two primary parameters:
- Pulse Energy: Ranged from 0.1 µJ (low energy) to 1.6 µJ (high energy).
- Exposure Time: Varied from 10 s up to 240 s (corresponding to 1M to 24M pulses at 100 kHz).
3D Confocal PL Spectroscopy: Micromarks were analyzed at room temperature (25 °C) using two distinct excitation wavelengths:
- 532 nm excitation: Primarily used to study NV⁰ and NV^- centers.
- 405 nm excitation: Used to study highly aggregated centers (N3, H3, H4) and the resulting H-band.
Data Normalization: PL spectra were corrected for depth-dependent confocal effects by using the diamond Raman line intensity (at 428 nm or 573 nm) as an internal standard, ensuring accurate comparison of center concentrations across different depths.
Transformation Mapping: Spectral changes were mapped against pulse energy and exposure time to identify the underlying chemical processes, including low-energy aggregation (e.g., A + V → H3) and high-energy dissociation (e.g., H4 → N3 + NV).

Commercial Applications

The controlled, subsurface creation of specific optical centers in diamond is crucial for advanced technologies in several high-value sectors.

Diamond Photonics: Fabrication of integrated 3D optical circuits, waveguides, and couplers deep within the diamond substrate, leveraging the high refractive index and stability of diamond.
Quantum Technology: High-density, deterministic creation of Nitrogen-Vacancy (NV) centers, which serve as solid-state qubits for quantum computing and highly sensitive magnetometers for quantum sensing.
High-Value Gem Security: Implementation of permanent, subsurface, photoluminescent track-and-trace markers (e.g., QR codes) for anti-counterfeiting in natural and synthetic diamonds.
Micro-Electrooptical Devices: Direct laser writing enables the creation of complex, multi-layered microstructures for integrated optical components and sensors that require high thermal and chemical stability.
Advanced Micromachining: Utilizing ultrashort pulse laser processing for precise, non-thermal structural patterning and modification of transparent, ultra-hard materials like diamond.

View Original Abstract

Micromarks were formed in bulk natural IaAB-type diamond laser-inscribed by 515 nm 0.3 ps femtosecond laser pulses focused by a 0.25 NA micro-objective at variable pulse energies in sub-picosecond visible-range laser regimes. These micromarks were characterized at room temperature (25 °C) by stationary 3D confocal photoluminescence (PL) microspectroscopy at 405 nm and 532 nm excitation wavelengths. The acquired PL spectra exhibit the increasing pulse-energy-dependent yield in the range of 550-750 nm (NV0, NV− centers) at the expense of the simultaneous reciprocal reduction in the blue-green (490-570 nm, H-band centers) PL yield. The detailed analysis indicates low-energy intensity rise for H-band centers as an intermediate product of vacancy-mediated dissociation of B1 and B2 centers, with H4 centers converting to H3 and NV centers at higher pulse energies, while the laser exposure effect demonstrates the same trend. These results will help solve the problem of direct laser writing technology, which is associated with the writing of micromarks in bulk natural diamond, and promising three-dimensional micro-electrooptical and photonic devices in physics and electronics.

Tech Support

Original Source

DOI: https://doi.org/10.3390/photonics10020135

References

2017 - Laser writing of coherent colour centres in diamond [Crossref]
2019 - Femtosecond laser written photonic and microfluidic circuits in diamond [Crossref]
2016 - Diamond photonics platform enabled by femtosecond laser writing [Crossref]
2019 - Laser writing of individual nitrogen-vacancy defects in diamond with near-unity yield [Crossref]
2021 - Broadband and fine-structured luminescence in diamond facilitated by femtosecond laser driven electron impact and injection of “vacancy-interstitial” pairs [Crossref]