A fiber disk laser
is a fiber laser
A fiber laser or fibre laser is a laser in which the active gain medium is an optical fiber doped with rare-earth elements such as erbium, ytterbium, neodymium, dysprosium, praseodymium, and thulium. They are related to doped fiber amplifiers, which provide light amplification without lasing...
with transverse delivery of the pump
Laser pumping is the act of energy transfer from an external source into the gain medium of a laser. The energy is absorbed in the medium, producing excited states in its atoms. When the number of particles in one excited state exceeds the number of particles in the ground state or a less-excited...
light. They are characterized by the pump beam not being parallel to the active core of the optical fiber
An optical fiber is a flexible, transparent fiber made of a pure glass not much wider than a human hair. It functions as a waveguide, or "light pipe", to transmit light between the two ends of the fiber. The field of applied science and engineering concerned with the design and application of...
(as in a double-clad fiber
Double-clad fiber is a class of optical fiber with a structure consisting of three layers of optical material instead of the usual two. The inner-most layer is called the core. It is surrounded by the inner cladding, which is surrounded by the outer cladding...
), but directed to the coil of the fiber at an angle (usually, between 10 and 40 degrees). This allows use of the specific shape of the pump beam emitted by the laser diode
The laser diode is a laser where the active medium is a semiconductor similar to that found in a light-emitting diode. The most common type of laser diode is formed from a p-n junction and powered by injected electric current...
, providing the efficient use of the pump.
Fiber disk lasers should not be confused with the laser disks (disk-shaped devices for storage and reading of information with laser beam) nor the disk laser
A disk laser or active mirror is a type of solid-state laser characterized by a heat sink and laser output that are realized on opposite sides of a thin layer of active gain medium...
or "active mirror", which is a laser with a thin active layer where the heat sink is realized in a direction opposite to that of propagation of the output beam.
Realizations of fiber disk lasers
First disk lasers were developed in the Institute for Laser Science
The Institute for Laser Scienceis a department of the University of Electro Communications, located near Tokyo, Japan.-Location:The Institute for Laser Science is located at 1-5-1 Chofugaoka, Chofu, Tokyo, 182-8585, Japan...
Several realizations of fiber disk lasers were reported. The fiber disk laser is so named because the fiber is tightly coiled. Typically, no special feedback for the laser frequency is required, as the small reflection at end of the fiber is sufficient to provide efficient operation. In this case, both ends of the coiled fiber can be used as output.
Application and power scaling
Fiber disk lasers are used for cutting of metal (up to few mm thick), welding
Welding is a fabrication or sculptural process that joins materials, usually metals or thermoplastics, by causing coalescence. This is often done by melting the workpieces and adding a filler material to form a pool of molten material that cools to become a strong joint, with pressure sometimes...
Pattern welding is the practice in sword and knife making of forming a blade of several metal pieces of differing composition that are forge-welded together and twisted and manipulated to form a pattern. Often called Damascus steel, blades forged in this manner often display bands of slightly...
. The disk-shaped configuration allows efficient heat dissipation (usually, the disks are cooled with flowing water)); allowing power scaling
Power scaling of a laser is increasing its output power without changing the geometry, shape, or principle of operation. Power scalability is considered an important advantage in a laser design....
. When the increase of the length of the fiber becomes limited by stimulated scattering, additional power scaling can be achieved by combining several fiber disk lasers into a stack.
The spiral-coiled configuration is not the only possible arrangement; any other scheme of stacking of optical fibers with lateral delivery of pump can also be called a fiber disk laser, even if the resulting shape of the device is not circular. The term fiber disk laser
applies to the concept of lateral delivery of pump to the active optical fiber rather than specifically to a disk-shaped device. The optimal shape of the fiber disk laser may depend on the properties of the beam of pump available, as well as on the specific application.