In laser safety, what does the term "optical density" refer to?

Optical density refers to the measure of a material's ability to attenuate or protect against laser light. It is a critical concept in laser safety, as it quantifies how much laser light is absorbed or blocked by protective eyewear, filters, or other safety measures. A higher optical density signifies a greater capacity for a material to reduce the intensity of laser light reaching the eyes, thus offering better protection for individuals working in environments where lasers are used.

Understanding optical density is essential for selecting appropriate safety equipment and ensuring adequate protection against potentially harmful laser radiation. The other options do not pertain to the concept of optical density: brightness relates to the light output from a laser, speed is a characteristic of the laser beam itself, and angle concerns the direction of laser light emission, none of which define the material's protective capability against laser exposure.