What Is Scratch-Dig?
Scratch-dig is a surface quality specification that describes the allowable imperfections on an optical surface. It consists of two numbers, such as 60-40 or 10-5, written according to US military standard MIL-PRF-13830B.
The first number (e.g., 60 or 10) refers to the maximum width in micrometers of scratches that are permitted. The second number (e.g., 40 or 5) refers to the largest permitted dig (pits, pits, and pits) diameter in micrometers.
Common Scratch-Dig Grades
| Grade | Scratch (μm) | Dig (μm) | Typical Use |
|---|---|---|---|
| 10-5 | 10μm | 50μm | High-power lasers, interferometry |
| 20-10 | 20μm | 100μm | Imaging optics, microscopy |
| 40-20 | 40μm | 200μm | General industrial, sensing |
| 80-60 | 80μm | 600μm | Consumer optics, illumination |
How to Read Scratch-Dig Numbers
Lower numbers mean higher quality. A 10-5 surface is significantly cleaner than 60-40. However, higher quality comes at higher cost and longer lead times.
For laser applications, the scratch-dig specification is critical because surface imperfections can cause beam scatter, absorption, and even damage at high power densities.
Choosing the Right Grade
Consider your application carefully:
- High-power laser systems: 20-10 or better. Scratches absorb laser energy and cause thermal damage.
- Imaging and microscopy: 40-20 to 60-40 depending on resolution requirements.
- Illumination and sensing: 60-40 to 80-60 typically sufficient.
- Interferometry: 10-5 or better to avoid phase errors.
Our Standard Offerings
Nova Component offers 40-20 as standard surface quality across most product lines, with 20-10 and 10-5 available as upgraded options. Contact our engineering team for custom specifications.