Glossary

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Neutral Density Filter

A type of filter with a metallic coating that yields a constant attenuation, or optical density, value over a range of wavelengths (i.e. spectrally flat). It is useful for attenuating, or reducing, the amount of light in a laser or high intensity light application.

See also Optical Density (OD), Filter, Continuously Variable Apodizing Filter

Noise

Caused by the unwanted spontaneous emission of light from a laser medium resulting in reduced optical performance.

See also Noise Equivalent Power (NEP)

Noise Equivalent Power (NEP)

The incident light power required to produce a signal on a detector that is equal to the noise. In this case, the signal-to-noise ratio is equal to one.

See also Noise, Detectivity, Signal-to-Noise Ratio (SNR)

Non-Polarizing Beamsplitter

A type of beamsplitter that splits the incident light by a specific percentage without altering the polarization state of the transmitted or reflected light.

See also Beamsplitter, Polarization

Normal Load Capacity

The maximum downward (compression) load or force that can be applied to a mechanical component perpendicular to the mounting surface. The center of force, or the center of gravity, of the load must be located in the center of the mounting surface.

See also Inverted Load Capacity, Moment Load

Notch Filter

A type of filter designed to block a pre-selected bandwidth while transmitting all other wavelengths within the design range of the filter. Manufactured using the dielectric stack method which involves using a series of thin layers of dielectric materials, of alternating refractive index.

See also Bandwidth, Dielectric Coating, Filter, Rugate Notch Filter

Nth Order

Multiple combinations of wavelength and integer order values that will satisfy any given groove spacing, angle of incidence, and diffracted angle calculated from the grating equation. Gratings are generally specified in terms of first order diffraction since efficiency decreases with higher orders.

Numerical Aperture (NA)

The sine of the vertex angle of the largest cone of meridional rays that can enter or exit an optical system (such as a lens or an optical fiber). In other words, it governs the amount of light entering or exiting a system.

Nyquist Limit

The limiting resolution of a camera's sensor, generally defined as being one half the sampling frequency. Typically measured in number of pixels per mm.

See also Pixel