High aspect ratio diamond nanosecond laser machining
At a Glance
Section titled âAt a Glanceâ| Metadata | Details |
|---|---|
| Publication Date | 2023-06-15 |
| Journal | Applied Physics A |
| Authors | Natalie C. Golota, David Preiss, Zachary P. Fredin, Prashant Patil, Daniel Banks |
| Institutions | MIT-Harvard Center for Ultracold Atoms, Massachusetts Institute of Technology |
| Citations | 16 |
| Analysis | Full AI Review Included |
Executive Summary
Section titled âExecutive SummaryâThis research demonstrates advanced nanosecond (ns) laser machining techniques for fabricating high aspect ratio (AR) structures in Type Ib HPHT diamond, focusing on maximizing AR and minimizing laser-induced damage.
- Maximum Aspect Ratio Achieved: A maximum AR of 66:1 (with an average of ~40:1) was achieved using rotary assisted drilling combined with high pulse accumulation (> 1.68 M equivalent pulses).
- Precision Taper Control: Low-taper 10:1 AR tubes were fabricated with a minimum internal taper angle of 0.11°, significantly below the Gaussian beam divergence angle (1.38°).
- Ablation Regimes: Two distinct ablation regimes were identified during percussion drilling: Gentle (low fluence, subject to incubation effects) and Strong (high fluence, resulting in greater hole diameter eccentricity).
- Damage Characterization: High-energy ns laser irradiation induced significant internal tensile strain, increasing up to 36% (48-55.4 MPa) in the crystal lattice, confirmed via confocal Raman spectroscopy.
- Strain Mitigation: The laser-induced strain was successfully reduced by up to ~50% and homogenized across the sample following a 24-hour heat treatment at 600 °C in air.
- Method Accessibility: The results were achieved using a commercially available ns laser system, providing an accessible method for fabricating high-performance diamond microstructures.
Technical Specifications
Section titled âTechnical Specificationsâ| Parameter | Value | Unit | Context |
|---|---|---|---|
| Laser Wavelength | 532 | nm | Diode-pumped Nd:YAG system |
| Pulse Duration | ~20 | ns | Q-switched operation |
| Repetition Rate | 5 | kHz | Fixed operating frequency |
| Maximum Average Power | 2.97 | W | System limit |
| Max Aspect Ratio (Rotary Drilling) | 66:1 (Avg 40:1) | 1:1 | Achieved with > 1.68 M equivalent pulses |
| Max Aspect Ratio (Percussion Drilling) | 22.4 ± 1.8 | 1:1 | Achieved with 10,000 pulses at 177 ”J |
| Minimum Internal Taper Angle | 0.11-0.17 | ° | Taper excluding chamfer in 10:1 AR tubes |
| Gentle Ablation Threshold Fluence (10,000 pulses) | 12.4 ± 1.4 | J/cm2 | Ablation threshold decreases with pulse number |
| Single Pulse Ablation Threshold Fluence | 29.5 ± 1.3 | J/cm2 | Highest threshold observed |
| Incubation Coefficient | 0.919 ± 0.008 | N/A | Observed in gentle ablation regime |
| Maximum Induced Tensile Strain | 55.4 | MPa | Observed after 592 ”J finishing passes |
| Strain Reduction Post-Treatment | ~50 | % | Reduction of laser-induced strain after annealing |
| Heat Treatment Parameters | 600 | °C | 24 h duration in air (atmospheric pressure) |
| Raman Shift/Strain Conversion | 360 | MPa/cm-1 | Linear relationship used for strain mapping |
Key Methodologies
Section titled âKey Methodologiesâ- Material Selection: Used Type Ib HPHT single crystal diamond with four-point 100 crystal orientation.
- Percussion Hole Drilling: Performed using single pulse energies ranging from 6.8 to 594 ”J. Hole geometry was characterized using microCT (2.1 ”m voxel size) to define Gentle and Strong ablation regimes.
- Rotary Assisted Drilling (High AR): Employed a custom apparatus using a direct drive rotary stage (66.6 RPM). High AR was achieved by translating the diamond stock while maintaining laser position and negatively incrementing the focus into the material (up to 250 ”m depth increments).
- Low Taper Tube Drilling (10:1 AR): Inner diameter taper was minimized by varying the irradiation profile, specifically using ramped pulse energy during initial rough cuts and final finishing passes. This technique optimizes debris and vapor ejection dynamics to reduce beam attenuation.
- Chamfer Control: The entrance chamfer (a 100-200 ”m deep feature) was found to be positively correlated with single pulse energy, requiring careful control or subsequent removal if detrimental.
- Strain Mapping: Confocal Raman spectroscopy (532 nm, 15 mW power) was used on cross-sectioned samples to map internal strain distribution and confirm the presence of surface localized sp2 carbon (graphite/amorphous carbon).
- Post-Processing Annealing: Oxidative heat treatment was applied at 600 °C for 24 hours in ambient air to remove surface graphite and relieve non-equilibrium bond distances, resulting in strain homogenization and reduction.
Commercial Applications
Section titled âCommercial ApplicationsâThe ability to machine high-precision, low-taper, high-AR structures in diamond using accessible nanosecond lasers supports several advanced technological fields:
- Nuclear Magnetic Resonance (NMR): Fabrication of ultra-low taper diamond sample holding tubes (rotors) required for high-speed pneumatic rotation (> 7 x 106 RPM) in MAS NMR research.
- Quantum Technology: Manufacturing microstructures for next-generation quantum devices, including those based on nitrogen-vacancy (NV) centers, where precise geometry and minimal lattice strain are critical.
- Micro-Electromechanical Systems (MEMS): Production of high-strength diamond components for MEMS devices, leveraging diamondâs superior mechanical properties.
- Microfluidics and Sensing: Creation of biocompatible microfluidic channels and spectroscopic devices, benefiting from diamondâs chemical inertness and optical transparency.
- High-Power Electronics: Fabrication of thermally optimized microstructures for power electronics and heat sinks, utilizing diamondâs exceptional thermal conductivity.