Fabrication of the optical lens on single-crystal germanium surfaces using the laser-assisted diamond turning
At a Glance
Section titled âAt a Glanceâ| Metadata | Details |
|---|---|
| Publication Date | 2024-04-25 |
| Journal | The International Journal of Advanced Manufacturing Technology |
| Authors | Hanheng Du, Yidan Wang, Yuhan Li, Yintian Xing, Sen Yin |
| Institutions | Beihang University, Shenzhen Polytechnic |
| Citations | 8 |
| Analysis | Full AI Review Included |
Technical Documentation & Analysis: Ultra-Precision Diamond Materials for Laser-Assisted Turning
Section titled âTechnical Documentation & Analysis: Ultra-Precision Diamond Materials for Laser-Assisted TurningâExecutive Summary
Section titled âExecutive SummaryâThis research validates the In situ Laser-Assisted Diamond Turning (ILADT) process as a highly effective method for the ultra-precision fabrication of optical lenses from hard and brittle materials, specifically single-crystal germanium (Ge). The success of this technique relies fundamentally on the quality and precision of the Single-Crystal Diamond (SCD) cutting tool.
- Process Validation: ILADT successfully combined laser heating and Single-Point Diamond Turning (SPDT) to machine high-quality aspheric optical lenses on brittle Ge substrates.
- Superior Surface Quality: The ILADT process achieved an exceptional surface roughness (Sa) of 0.909 nm on the final optical lens, significantly outperforming traditional SPDT (1.328 nm Sa).
- Enhanced Machinability: Laser assistance increased the critical depth-of-cutting by 64.1% (from 79.32 nm to 130.19 nm) and reduced the von Mises equivalent stress in the shear zone by 16.4%.
- High Accuracy: The measured profile error of the aspheric lens was 0.135 ”m, demonstrating high machining accuracy suitable for advanced optics.
- Material Integrity: Raman spectroscopy confirmed that laser heating introduced a minor compressive stress (shift from 303 to 305 cm-1), which stabilizes the crystal structure and mitigates surface defects (micro-cracks).
- Core Requirement: The process demands SCD cutting tools with extremely sharp edges (< 100 nm) and precise geometry (e.g., negative rake angle of -35°) to handle the localized heating and material removal.
- Application Relevance: This technology is critical for manufacturing high-performance optical components requiring intricate geometries and nanoscale surface finishes for aerospace, defense, and IR telecommunications.
Technical Specifications
Section titled âTechnical SpecificationsâThe following data highlights the performance metrics achieved using the ILADT process compared to traditional SPDT, emphasizing the critical role of the SCD cutting tool.
| Parameter | Value | Unit | Context |
|---|---|---|---|
| Optical Lens Profile Error (ILADT) | 0.135 | ”m | High machining accuracy achieved. |
| Optical Lens Surface Roughness (Sa, ILADT) | 0.909 | nm | Measured on 213.78 ”m x 213.78 ”m area of the final lens. |
| Surface Roughness Reduction (ILADT vs. SPDT) | 31.6 | % | Sa decreased from 1.328 nm (SPDT) to 0.909 nm (ILADT). |
| Critical Depth-of-Cutting (ILADT) | 130.19 | nm | 64.1% improvement over SPDT (79.32 nm). |
| Von Mises Stress Reduction | 16.4 | % | Reduction in the shear zone due to laser assistance. |
| Compressive Stress Indication (Raman Shift) | 303 to 305 | cm-1 | Shift in LO phonon mode peak, indicating enhanced material integrity. |
| SCD Tool Rake Angle | -35 | ° | Negative rake angle required for laser path clearance. |
| SCD Tool Radius | 0.497 | mm | Specific geometry used for machining. |
| Laser Source / Power | Nd: YAG / 1.75 | W | Used for localized heating and material softening. |
| Finishing Feed Rate | 0.8 | ”m/rev | Ultra-precision feed rate during final pass. |
Key Methodologies
Section titled âKey MethodologiesâThe ILADT process is a highly specialized ultra-precision technique requiring precise control over the diamond tool, laser energy, and motion systems.
- Hardware Integration: The system utilized a 3-axis ultraprecision lathe (Moore 450 UPL) integrated with a laser control module (Micro-LAM Optimus T2) fixed on the Z-axis.
- Workpiece Preparation: Single-crystal Germanium (111) samples (10 mm diameter) were fixed on the C-axis using a custom fixture.
- Diamond Tool Selection: A Natural Single-Crystal Diamond (SCD) cutting tool was selected, featuring a negative rake angle (-35°) to accommodate the laser beam path and a sharp cutting edge (< 100 nm).
- In Situ Heating: A 1.75 W Nd: YAG laser beam was directed through the SCD cutting tool to the cutting zone, locally heating and softening the brittle Ge material immediately prior to material removal.
- Machining Parameters: Spindle speed was maintained at 83 RPM. Roughing was performed at 2 ”m/rev, followed by finishing at 0.8 ”m/rev to achieve nanoscale surface quality.
- Metrology: Surface roughness (Sa, Sq, Sz) was characterized using a white light interferometer. The full aspheric profile and profile error were measured using contact form metrology (Taylor Hobson Form TalySurf PGI 1240).
6CCVD Solutions & Capabilities
Section titled â6CCVD Solutions & CapabilitiesâThe successful implementation of ILADT hinges on the availability of high-quality, precisely engineered Single-Crystal Diamond (SCD) tools. 6CCVD specializes in providing the advanced MPCVD diamond materials and customization services necessary to replicate and extend this cutting-edge research.
Applicable Materials
Section titled âApplicable MaterialsâThe paper utilized a natural SCD tool. 6CCVD offers superior, highly consistent MPCVD diamond materials ideal for ultra-precision machining applications:
| Research Requirement | 6CCVD Material Solution | Technical Advantage |
|---|---|---|
| SCD Cutting Tool Blanks | Ultra-High Purity Single Crystal Diamond (SCD) | MPCVD SCD offers superior purity and crystallographic consistency compared to natural diamond, ensuring longer tool life and more consistent nanoscale edge sharpness (< 1nm Ra polishing capability). |
| High-Performance Optics | Optical Grade SCD Plates | For applications requiring diamond optics (e.g., high-power IR windows), 6CCVD offers SCD plates up to 500 ”m thick with Ra < 1 nm polishing, ensuring minimal scattering and absorption loss. |
| Advanced Tooling/Fixtures | Polycrystalline Diamond (PCD) Substrates | Available in large formats (up to 125 mm diameter) and thicknesses up to 10 mm, ideal for fabricating robust, custom fixtures or large-area diamond components. |
| Thermal Management | High Thermal Conductivity SCD | Essential for managing heat dissipation in the laser-assisted cutting zone and for high-power optical systems. |
Customization Potential
Section titled âCustomization PotentialâThe ILADT process requires highly specific tool geometries and precise mounting solutions. 6CCVDâs in-house engineering and fabrication capabilities directly support these needs:
- Custom Tool Blanks: We provide SCD blanks tailored to specific dimensions and orientations required for fabricating tools with complex geometries, such as the negative rake angle (-35°) and specific nose radius (0.497 mm) used in this study.
- Ultra-Precision Polishing: 6CCVD guarantees surface finishes of Ra < 1 nm on SCD materials, ensuring the cutting tool edge is maintained at the nanoscale sharpness required for ductile-regime machining of brittle materials like Ge.
- Custom Metalization Services: The integration of the SCD tool onto the laser module and lathe spindle often requires robust mounting. We offer internal metalization services (Au, Pt, Pd, Ti, W, Cu) for creating stable, high-adhesion interfaces for tool fixturing and thermal management.
- Large Format Capability: While this study used a 10 mm Ge sample, 6CCVD can supply PCD plates up to 125 mm in diameter, enabling the scale-up of ultra-precision machining techniques for larger optical components.
Engineering Support
Section titled âEngineering SupportâThe successful mitigation of micro-cracks and the introduction of beneficial compressive stress via ILADT are complex material science challenges. 6CCVDâs in-house PhD team specializes in the material properties and performance of diamond under extreme conditions.
We offer expert consultation on:
- Material Selection: Guiding researchers in selecting the optimal SCD crystal orientation and purity for specific ultra-precision machining tasks (e.g., optimizing tool wear resistance under high thermal load).
- Stress and Defect Analysis: Assisting with material characterization methods, including Raman spectroscopy analysis, to monitor and control the residual stress and structural integrity of machined surfaces for similar Laser-Assisted Diamond Turning projects.
- Global Logistics: We provide reliable global shipping, including DDU (default) and DDP options, ensuring timely delivery of critical materials worldwide.
For custom specifications or material consultation, visit 6ccvd.com or contact our engineering team directly.
View Original Abstract
Abstract Single-crystal germanium, as an excellent infrared optical material, has been widely applied in X-ray monochromators, night vision systems, and gamma radiation detectors. However, how to obtain high-quality optical lenses on their surfaces still faces challenges due to their hard and brittle properties. To this end, this paper proposes the in situ laser-assisted diamond turning (ILADT) process, which is the combination of a laser heating technique and a single-point diamond turning process. The in situ laser heating technique is employed to enhance the surface quality of the workpiece material, while the single-point diamond turning process is utilized to fabricate optical lenses. Experimental results showed that optical lenses with high surface quality were successfully machined. The profile error is 0.135 ÎŒm, indicating the high machining accuracy. The surface roughness Sa of the aspheric lens is 0.909 nm, indicating the high machining quality achieved by the proposed ILADT process. Therefore, this study provides an effective approach for producing high-quality optical lenses on single-crystal germanium surfaces, which holds great promise for future applications in the manufacturing of optical lenses with exceptional quality.
Tech Support
Section titled âTech SupportâOriginal Source
Section titled âOriginal SourceâReferences
Section titled âReferencesâ- 2023 - Augmented Reality [Crossref]