Photoluminescent Microbit Inscripion Inside Dielectric Crystals by Ultrashort Laser Pulses for Archival Applications

At a Glance

Metadata	Details
Publication Date	2023-06-24
Journal	Micromachines
Authors	S. I. Kudryashov, П. А. Данилов, Nikita Smirnov, Evgeny V. Kuzmin, Alexey Rupasov
Institutions	P.N. Lebedev Physical Institute of the Russian Academy of Sciences
Citations	3
Analysis	Full AI Review Included

Technical Documentation & Analysis: Photoluminescent Microbit Inscription in Diamond

This document analyzes the research on ultrashort-pulse laser inscription of photoluminescent microbits in dielectric crystals, focusing on the application of 6CCVD’s specialized MPCVD diamond materials for high-density, thermally stable archival optical storage.

Executive Summary

This research validates the use of bulk diamond as a superior platform for 3D archival optical memory, leveraging the creation of Nitrogen-Vacancy (NV) color centers via femtosecond laser inscription.

Application: Novel optomechanical memory storage platforms utilizing photoluminescent microbits for archival data.
Material Superiority: Diamond (NV centers) demonstrated exceptional thermal stability, persisting up to ≈1200 °C, significantly outperforming fluorides (LiF, CaF₂) which degrade at 300 °C.
Inscription Method: Sub-filamentation regime inscription using 525 nm, 0.2 ps ultrashort laser pulses focused by a 0.65 NA objective.
Key Achievement: Successful creation and 3D confocal visualization of NV⁰ (575 nm) and NV⁻ (637 nm) color centers in bulk diamond at a depth of 120 µm.
Storage Potential: Preliminary evaluation suggests a bulk microbit density of 25 Gbits/cm³, with potential for few-fold increases using higher Numerical Aperture (NA) focusing systems.
6CCVD Value: We provide the high-purity, custom-dimension Single Crystal Diamond (SCD) required to optimize NV center creation and scale this technology into commercial memory platforms.

Technical Specifications

Parameter	Value	Unit	Context
Material Platform	Natural Diamond (IaA-type)	-	Used for NV center inscription
Writing Wavelength	525	nm	Second harmonic of Yb-crystal laser
Pulse Duration	0.2	ps	Ultrashort pulse regime
Repetition Rate	80	MHz	Used for color center accumulation
Focusing NA	0.65	-	Used for sub-filamentation focusing
Inscription Depth	120	µm	Depth of microbit array inside diamond
Peak Laser Intensity	<30	TW/cm²	Used in sub-filamentary regime
NV^- Zero-Phonon Line (ZPL)	637	nm	Primary photoluminescent signal
NV⁰ Zero-Phonon Line (ZPL)	575	nm	Neutral photoluminescent signal
Thermal Stability (Diamond)	≈1200	°C	Archival stability limit for NV centers
Evaluated Bulk Density	25	Gbits/cm³	Based on 2 µm lateral / 11 µm vertical separation
Minimal Lateral Separation	2	µm	Achieved resolution for robust read-out

Key Methodologies

The experiment utilized a delicate laser micromachining process combined with high-resolution confocal microscopy for characterization.

Material Preparation: 2 mm thick IaA-type natural diamond slabs were utilized, optically transparent at the 525 nm writing wavelength.
Laser Source: Second-harmonic (525 nm) pulses from a TEMA Yb-crystal laser (0.2 ps pulsewidth, 80 MHz repetition rate) were used.
Inscription Setup: Pulses (up to 50 nJ) were focused in a sub-filamentary regime using a 0.65 NA micro-objective to create ≈1 µm wide spots inside the crystal (120 µm depth).
Microbit Encoding: Photoluminescent microbits were inscribed as a function of pulse energy (E) and exposure time, creating arrays with variable transverse (1-5 µm) and longitudinal (1-28 µm) spacings.
Annealing: Diamond samples were annealed in an evacuated oven for 1 hour at temperatures ranging from 25 °C to 1200 °C to test thermal stability.
Read-Out/Characterization: 3D-scanning confocal photoluminescence (PL)/Raman microscopy (532 nm CW pump laser, 100× magnification, NA = 1.45) was used to measure relative intensity, spatial dimensions, and spectral features (NV⁰ and NV⁻ centers).

6CCVD Solutions & Capabilities

6CCVD is uniquely positioned to supply the advanced MPCVD diamond materials necessary to replicate, optimize, and scale this archival memory research. The exceptional thermal stability of NV centers in diamond (up to 1200 °C) makes it the definitive material choice for long-term archival storage.

Applicable Materials

To maximize the efficiency and uniformity of NV center creation, high-quality, low-defect Single Crystal Diamond (SCD) is required.

Research Requirement	6CCVD Material Solution	Technical Advantage
High Purity Substrate	Optical Grade SCD	Ultra-low defect density ensures controlled, uniform NV center formation, crucial for reliable data encoding.
Controlled Nitrogen	Tailored SCD	While the paper used IaA natural diamond (N ≈ 130 ppm), 6CCVD can supply SCD with precisely controlled nitrogen concentrations, optimizing the NV⁻/NV⁰ ratio and PL yield.
Bulk Modification	SCD Substrates (up to 10 mm)	We provide SCD wafers up to 500 µm thick, and substrates up to 10 mm thick, enabling deep 3D inscription layers far exceeding the 120 µm depth demonstrated.
High NA Interface	SCD Polishing (Ra < 1 nm)	Achieving the targeted 1-1.5 µm resolution requires high-NA focusing. Our ultra-smooth polishing (Ra < 1 nm) minimizes scattering and aberration at the input surface, maximizing focal quality.

Customization Potential

The ability to scale this technology relies on custom material engineering, a core competency of 6CCVD.

Custom Dimensions: We offer SCD plates and wafers in custom sizes and thicknesses (0.1 µm to 500 µm), allowing researchers to move beyond small natural diamond slabs toward scalable, engineered platforms.
Advanced Polishing: To facilitate the use of higher-NA objectives (NA > 0.65) necessary for increasing storage density beyond 25 Gbits/cm³, 6CCVD guarantees Ra < 1 nm surface roughness on SCD, ensuring optimal optical coupling and minimal wavefront distortion.
Metalization Services: While not used in this specific inscription study, future integration of diamond microbits into optomechanical or quantum memory architectures may require electrical contacts or reflective layers. 6CCVD provides in-house deposition of standard metals including Ti, Pt, Au, Pd, W, and Cu.

Engineering Support

6CCVD’s in-house PhD team specializes in defect engineering and material optimization for quantum and optical applications. We can assist researchers in:

Nitrogen Doping Control: Fine-tuning the nitrogen concentration during MPCVD growth to optimize the density and charge state (NV⁻ vs. NV⁰) of the photoluminescent microbits.
Post-Processing Optimization: Advising on optimal annealing protocols (temperature and duration) to maximize NV center yield and ensure the highest possible thermal stability for archival applications.
Material Selection: Providing expert consultation on selecting the ideal SCD thickness and surface finish for specific ultrashort-pulse laser parameters and NA requirements.

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

View Original Abstract

Inscription of embedded photoluminescent microbits inside micromechanically positioned bulk natural diamond, LiF and CaF2 crystals was performed in sub-filamentation (geometrical focusing) regime by 525 nm 0.2 ps laser pulses focused by 0.65 NA micro-objective as a function of pulse energy, exposure and inter-layer separation. The resulting microbits were visualized by 3D-scanning confocal Raman/photoluminescence microscopy as conglomerates of photo-induced quasi-molecular color centers and tested regarding their spatial resolution and thermal stability via high-temperature annealing. Minimal lateral and longitudinal microbit separations, enabling their robust optical read-out through micromechanical positioning, were measured in the most promising crystalline material, LiF, as 1.5 and 13 microns, respectively, to be improved regarding information storage capacity by more elaborate focusing systems. These findings pave a way to novel optomechanical memory storage platforms, utilizing ultrashort-pulse laser inscription of photoluminescent microbits as carriers of archival memory.

Tech Support

Original Source

DOI: https://doi.org/10.3390/mi14071300

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