N

Nanometer (nm)

A unit of length in the International System of Units (SI) equal to one-billionth (10^-9) of a meter. The usual measure of light wavelengths. Visible light ranges from about 400nm in the violet to about 760nm in the deep red.

Nanosecond

One-billionth (10^-9) of a second. Longer than a picosecond or femto- second, but shorter than a microsecond. Associated with Q-switched lasers.

Nd:Glass laser

A solid-state laser of neodymium glass offering high power in short pulses. An Nd-doped glass rod used as a laser medium to produce 1064nm light.

Nd:YAG laser

A solid-state laser that uses a rod of yttrium aluminum garnet (YAG) doped with neodymium to serve as the lasing medium.

Near field imaging

A solid-state laser imaging technique offering control of spot size and hole geometry, adjustable working distance, uniform energy distribution, and a wide range of spot sizes.

NEMA

Abbreviation for National Electrical Manufactures’ Association, a group that defines and recommends safety standards for electrical equipment.

Neodymium (Nd)

The rare earth element that is the active element in Nd:YAG laser and Nd:Glass lasers.

Neutral density filter

A gray filter that decreases the intensity of light without altering the wavelength.

Noise

Unwanted minor currents or voltages in an electrical system.

Nominal hazard zone (NHZ)

Describes the space within which the level of the direct, reflected, or scattered radiation during normal operation exceeds the applicable MPE. Exposure levels beyond the boundary of the NHZ are below the appropriate MPE level.

Nominal ocular hazard distance (NOHD)

The axial beam distance from the laser where the exposure or irradiance falls below the applicable exposure limit.

Numerical aperture (NA)

Expresses the ability of a lens to resolve fine detail in an object being observed. Equal to the refractive index of the lens multiplied by the sine of the cone angle of the lens. Generally measured with respect to an object or image point, and will vary as the point is moved.

where n₀ is the index of refraction of the medium surrounding the image (normally 1.0 for air), and q is the angle of light as it narrows to the focal point.