Brightness

Author: the photonics expert Dr. Rüdiger Paschotta (RP)

The term brightness should be used only for non-quantitative references, e.g. in the context of physiological sensations; that is recommended by the U.S. Federal Standard 1037C, for example. For actual quantitative references, one should usually use one of the following terms:

• The radiance is defined as optical power (radiant flux) per unit area and solid angle; its units are W cm⁻² sr⁻¹. This quantity is used in radiometry, where the physical properties of light and not its visual perception are relevant.
• The luminance is the luminous flux per unit area and solid angle, with units of candela per square meter (cd/m²). This is a quantity of photometry, where the spectral response of the human eye is taken into account.

Unfortunately, the term brightness is often somewhat inaccurately used instead of radiance or luminance.

In laser technology, the term brightness is often said to be higher for one type of laser than for another, for example, but rarely with an actual quantitative specification (some numbers and units). What is usually meant is the clearly defined term radiance. That implies e.g. that the brightness of a laser is increased if its beam quality is improved for a fixed output power level.

The term also occurs as part of composite terms:

• Brightness converters are essentially devices which receive optical radiation and emit radiation with a higher radiance. That is not possible with passive optical elements, but e.g. with certain optically pumped lasers.
• High brightness laser diodes are laser diodes which are optimized for a particularly high radiance (brightness).

More to Learn

Suppliers

The RP Photonics Buyer's Guide contains 16 suppliers for double-clad fibers. Among them:

Exail

Exail (formerly iXblue) offers a wide range of specialty optical fibers for lasers and amplifiers. We master erbium, erbium/ytterbium, ytterbium, thulium, holmium, thulium/holmium, neodymium, dysprosium, and phosphorous gain media. PM version are available, and Large Mode Area (LMA) or Very Large Mode Area (VLMA) versions as well. Depending of the requirement, single clad fibers are available for core pumping, double clad fibers for cladding pumping. Triple clad and all-glass structures are also available.

Fibercore

Fibercore offers a range of double-clad fibers including low index double-clad passive fiber providing high power handling capability with 1060 nm and 1550 nm variants, as well as all-silica double-clad passive fiber which combines both single-mode and multimode characteristics providing outstanding power handling over a full range of environmental conditions.

NKT Photonics

Our ytterbium-doped double-clad fibers feature the largest single-mode cores available. They have a high numerical aperture in the pump core/inner cladding for efficient pumping, compatible with both inexpensive and high-power broad-area emitting pumps. The single-mode signal travels in the large mode area to give high power levels and prevents nonlinearities. Need it packaged? Choose one of our aeroGAIN-ROD or aeroGAIN-BASE modules.

Le Verre Fluore

LVF offers a range of rare-earth doped double cladding single-mode and multimode fluoride fibers for high power laser generation. Most of them exhibit a double D-shape on the first cladding in order to improve the pump absorption.

Undoped double cladding single-mode and multimode fluoride fibers are also available.

Questions and Comments from Users