A flat window is fabricated by cutting, grinding, and polishing optical materials, making it the most fundamental and commonly used type of optical window. It is an optical flat with two surfaces that are parallel to each other. Its core function is to isolate the physical environment while allowing light signals to pass through with minimal distortion.
Does not introduce aberrations
Exhibits reflected ghost images
Experiences thermal lensing effects
| Material | H-K9L, UV Fused Silica, Calcium Fluoride, Sapphire, Magnesium Fluoride, Zinc Selenide, Silicon |
| Surface Flatness | ≤λ/10 |
| Backside Surface | Fine Ground or Polished |
| Thickness Tolerance | ±0.2mm |
| Diameter Tolerance | +0.0,-0.2mm |
| Focal Length Tolerance | ±2% |
| Parallelism | <3 arcmin |
| Surface Quality | 20/10-60/40 |
