The 31W00ML.1 Linear Variable Metallic ND Filter is a 79.4 x 25.4 mm linear variable metallic ND filter made of BK 7 glass with an OD of 0.08-2, and surface flatness of ≤2λ. This ND filter provides linearly varying attenuation or beamsplitting in the visible and NIR region. Attenuation is achieved by a thin film of aluminum protected with an overcoat, and variable beamsplitting is an added benefit of the inherent reflectivity of aluminum. The BK 7 substrate has a slight wedge between the faces to eliminate unwanted fringe patterns and cavity feedback, and the rear surface is also antireflection coated for the broadband visible range.
| Model | 31W00ML.1 |
|---|---|
| Type | Individual Filters |
| Thickness | 0.125 in. |
| Material | BK 7 |
| Surface Quality | 40-20 scratch-dig |
| Surface Flatness | ≤2λ |
| Optical Density | 0.08-2.0 |
| Wedge | 15 ±5 arc min |
| Wavelength Range | 430-700 nm |
| Thickness Tolerance | +0/-0.76 mm |
| Clear Aperture | ≥central 90% of length and 80% of width |
| Damage Threshold | 75 W/cm2 CW, 10 mJ/cm2 with 10 nsec pulses at 1064 nm, typical |
| Length X | 79.4 mm |
| Length (X), Width (Y) Tolerance | +0/-0.25 mm |
| Optical Density Tolerance | ±5% |
| Chamfers | 0.25–0.76 mm face width |
| Chamfers Angle/Tolerance | 45° ±15° |
| Cleaning | Non-abrasive method, acetone or isopropyl alcohol on lens tissue recommended |
