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 | Dalian University of Technology, Beihang University |
| Citations | 8 |
| Analysis | Full AI Review Included |
Executive Summary
Section titled âExecutive SummaryâThis research introduces the In situ Laser-Assisted Diamond Turning (ILADT) process for fabricating high-quality optical lenses on single-crystal germanium (Ge), a material known for its hardness and brittleness.
- Core Value Proposition: ILADT effectively mitigates micro-crack formation and enhances surface quality by combining laser heating with single-point diamond turning (SPDT).
- Machinability Enhancement: The critical depth-of-cutting for Ge was increased by 64.1% (from 79.32 nm to 130.19 nm) compared to traditional SPDT, demonstrating superior material removal capability.
- Surface Quality Achievement: The surface roughness (Sa) of the machined aspheric lenses was reduced by 31.6%, achieving a nanoscale finish of 0.909 nm.
- Accuracy: High machining accuracy was confirmed with a low profile error of 0.135 ”m for the complex aspheric lens geometry.
- Stress Mitigation: Raman spectroscopy revealed that laser heating introduced a minor, beneficial compressive stress (Raman shift from 303 cm-1 to 305 cm-1), which stabilizes the crystal structure and reduces surface defects.
- Process Efficiency: As a one-step process, ILADT avoids post-processing steps typically required for brittle materials, saving significant machining time.
Technical Specifications
Section titled âTechnical Specificationsâ| Parameter | Value | Unit | Context |
|---|---|---|---|
| Workpiece Material | Single-crystal Germanium (111) | N/A | Sample diameter 10 mm |
| Machining Process | In situ Laser-Assisted Diamond Turning (ILADT) | N/A | Combines laser heating and SPDT |
| Laser Source | Nd: YAG | N/A | Used for localized heating |
| Laser Power | 1.75 | W | Applied to the cutting zone |
| Spindle Speed | 83 | RPM | Constant for roughing and finishing |
| Finishing Feed Rate | 0.8 | ”m/rev | Used for final surface quality pass |
| Tool Rake Angle | -35 | ° | Natural single-crystal diamond (SCD) tool |
| Aspheric Lens Radius (R) | 5 | mm | Geometrical parameter |
| ILADT Surface Roughness (Sa) | 0.909 | nm | Machined optical lens quality |
| SPDT Surface Roughness (Sa) | 1.328 | nm | Traditional method comparison |
| ILADT Profile Error | 0.135 | ”m | Machining accuracy |
| ILADT Critical Depth-of-Cutting | 130.19 | nm | 64.1% improvement over SPDT (79.32 nm) |
| Von Mises Stress Reduction | 16.4 | % | Reduction in shear zone compared to SPDT |
| Raman Peak Shift (ILADT) | 305 | cm-1 | Indicates minor compressive stress |
Key Methodologies
Section titled âKey MethodologiesâThe ILADT process utilizes specialized hardware and precise parameter control to achieve ductile-regime machining of brittle germanium.
- Hardware Integration: The system combines a three-axis ultraprecision lathe (450 UPL, Moore Tool Company) with a laser control module (Optimus T2, Micro-LAM Inc.) fixed on the Z-axis.
- Workpiece and Tool Setup: Single-crystal germanium (111) was fixed on the C-axis. A natural single-crystal diamond (SCD) tool with a negative rake angle (-35°) and a 0.497 mm radius was used.
- In Situ Laser Heating: An Nd: YAG laser was set to 1.75 W and directed through the SCD tool onto the cutting zone. This localized heating softens the Ge, reducing cutting forces and promoting ductile material removal.
- Machining Parameters: The optical lens was fabricated using two sequential steps, both at a constant spindle speed of 83 RPM:
- Roughing: Feed rate of 2 ”m/rev.
- Finishing: Feed rate of 0.8 ”m/rev.
- Critical Depth Determination (Sculpturing): To quantify the ILADT advantage, sculpturing experiments were performed where the depth of cut progressively increased. This confirmed the 64.1% increase in critical depth-of-cutting.
- Characterization:
- Surface roughness (Sa, Sz) and 3D topography were measured using a white light interferometer.
- Full profile error (0.135 ”m) was measured using contact form metrology (Form TalySurf PGI 1240).
- Structural analysis and stress measurement were conducted using Raman spectroscopy.
Commercial Applications
Section titled âCommercial ApplicationsâThe ability of ILADT to produce high-quality, complex optical surfaces on hard, brittle materials like germanium opens doors for several high-value engineering sectors.
- Infrared (IR) Systems: Germanium is essential for IR optics. This technology enables the manufacturing of high-performance IR lenses, windows, and microlens arrays for:
- Night vision systems.
- Thermal imaging cameras.
- IR spectroscopy equipment.
- Aerospace and Defense: Fabrication of precision optical components requiring exceptional surface integrity and minimal scattering losses for:
- Guidance systems and sensors.
- Gamma radiation detectors.
- X-ray monochromators.
- Advanced Consumer Optics: Production of complex aspheric and freeform lenses with nanoscale surface quality for next-generation devices, such as:
- Mixed-reality and virtual reality (MR/VR) headsets (e.g., Apple Vision Pro).
- High-resolution digital cameras and projectors.
- Ultra-Precision Manufacturing: Applicable to other hard and brittle semiconductor materials (e.g., silicon) where traditional diamond turning is limited by micro-fracture and amorphization.
- Telecommunications: Manufacturing of optical components that require precise tolerances and high optical efficiency to minimize absorption losses.
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]