Precision Transparent PC Mirror Machining Case: A Key Optical Component for Terahertz Spectroscopy Systems

Background and Product Overview

High-tech applications in mid-infrared and terahertz (THz) radiation detection require making invisible radiation “visible” and delivering highly sensitive, easy-to-integrate detection solutions for research, material analysis, and precision measurement. To achieve this, the radiation signal must be guided accurately and consistently to the core detector, which demands a reliable optical path structure.

A key component of this system is the mirror, designed to achieve efficient reflection and focusing under strict angular conditions. Its tilted curved surface requires exceptionally high shape accuracy and surface quality, presenting one of the main technical challenges in the entire optical setup.

After completing prototyping, material verification, and process refinement, the customer entrusted WayKen with the batch production of this mirror. To ensure consistent quality in every unit, WayKen implemented precise machining strategies and strict inspection procedures, enabling reliable, repeatable parts for demanding optical applications.

Material Verification During the Prototyping Stage

Because the mirror requires an optical-grade surface finish, the initial material evaluation focused on comparing PMMA and PC.

PMMA offers higher transparency and excellent optical performance, and it can achieve a very smooth mirror finish after polishing. However, its lower toughness and heat resistance make it prone to deformation or cracking during vacuum aluminum coating, which can affect coating stability.

PC is slightly less transparent, but its higher toughness, heat resistance, and dimensional stability make it more reliable during machining and vacuum coating. It maintains structural integrity under vacuum conditions and provides better coating adhesion, making it more suitable for this mirror component.

Considering optical performance, machining stability, and coating compatibility, the customer ultimately selected transparent PC for this project.

Optimized Batch Machining Strategy for Consistency and Efficiency

This project involves about 200 transparent PC optical mirrors, which fall into small-batch custom production. Because the mirrors have complex curved surfaces and tight accuracy requirements, machining them one by one would be inefficient and could introduce cumulative errors from repeated clamping, affecting consistency across the batch.

1. Custom Fixture

To address this, we developed a fixture that allows three mirrors to be machined in parallel. All three parts are completed in a single setup on a five-axis machine. With a unified reference, identical tool paths, and synchronized machining, we achieved highly stable dimensional accuracy and surface consistency while significantly improving efficiency.

2. Unified Tool Diameter

To further ensure uniform surface roughness, we standardized the use of an R0.5 tool for all curved-surface machining. This provides a more consistent and predictable machine finish and reduces the amount of manual polishing required. More importantly, manual polishing inevitably introduces variation in pressure, which can affect flatness. By maximizing surface quality at the machining stage, we minimize the impact of hand polishing on the final optical geometry.

3. Surface Finishing

Achieving a high-reflectivity mirror finish on transparent PC requires two key conditions: an extremely smooth base surface and a coating that is uniform, stable, and firmly bonded.

3.1 Manual polishing

In practice, manual polishing is the first challenge. PC is relatively soft, making it difficult to maintain consistent pressure by hand. Any variation can distort the original contour and affect flatness. The surface must also remain free of pits and scratches, as these defects will be amplified after the aluminum coating.

To maintain control, we use a step-by-step polishing process, moving from 600-grit and 800-grit paper to 1100, 1500, and finally 2000. Each stage has strict limits on polishing time and material removal to prevent over-polishing and surface deformation.

3.2 PVD aluminum

The PVD aluminum stage introduces another level of sensitivity. The process is highly dependent on surface preparation, and even tiny scratches, particles, or dust can become visible in the final coating. Therefore, each part undergoes a surface inspection before coating, and the coating environment is kept strictly dust-free to minimize defects.

Through precise control of both polishing and coating, each mirror achieves high smoothness, strong reflectivity, and excellent consistency, enabling stable delivery even in small-batch production.

Feedback & Ongoing Support

The customer confirmed that all mirrors successfully passed functional testing and demonstrated stable performance in operation. The optical parameters met their requirements, and the precision and surface quality fully supported smooth THz system integration. They also confirmed continued orders for future batches.

Beyond this project, WayKen supports similar optical and precision components with controlled machining processes, consistent surface finishing, and reliable small-batch production.

If you are working on high-precision optical parts or complex transparent components, feel free to reach out to discuss your project.