The clear aperture is the pupil of the system that preserves all specifications defined by the manufacturer. It is always smaller than the diameter of the optic.
Optical density measures how well a component blocks light passing through it. A high optical density indicates very low transmission. OD is measured on a log scale.
Surface quality measures surface imperfections and is expressed by two numbers separated by a hyphen (scratch-dig). The first number refers to scratches and the second to digs or pits, where lower numbers indicate higher quality.
Thickness indicates the distance between two surfaces. Larger thickness allows for greater heat dissipation and higher resistance to stress in machining, blocking, and handling, however it increases weight and dispersion.
Cooled mounts are used in laser systems to control and stabilize the temperature. By actively dissipating heat away from these components, cooled mounts prevent excessive temperatures and consequent damage.
The CW damage threshold indicates the maximum power density that an optic can withstand without being damaged by a CW laser. Power Density (W/cm2) = P (W) / A (cm2).
The field of view (FOV) of an optical system is the viewable area of the object seen at any given time, and at a fixed orientation, by an observer or a device such as a camera, microscope, or telescope.
The focal length measures the strength of an optical system to converge (focus) or diverge light. It is related to the radius of curvature and inversely proportional to the optical power.
Surface Irregularity, Surface Flatness or Surface Figure is the maximum deviation from a fully flat face along the same lateral dimensions specified in fraction of reference wavelength.
It is the free space between the object plane (sample) and the first surface of the first element from the object in a complex lens (optical assembly) or the front edge of a single lens.