Fiber disk laser

A fiber disk laser is a fiber laser with transverse delivery of the pump light. They are characterized by the pump beam not being parallel to the active core of the optical fiber (as in a double-clad fiber), but is directed to the coil of the fiber with some angle (usually, between 10 and 40 degrees). This allows use of the specific shape of the pump beam emitted by the laser diode providing the efficient use of 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 or "active mirror", which is a laser with a thin active layer where the heat sink is realized in the direction opposite to the direction of propagation of the output beam.

Realizations of fiber disk lasers
First disk lasers were developed in the Institute for Laser Science, Japan. Several realizations of the fiber disk lasers were reported . The fiber in the fiber disk laser is coiled into a disk (see figure), hence the name. Typically, no special feedback for the laser frequency is required, the small reflection at end of the fiber is sufficient to provide the 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 and folding. The disk-shaped configuration allows the efficient heat sink (usually, the disks are cooled with flowing water)); allowing the power scaling. When the increase of the length of the fiber becomes limited by the processes of stimulated scattering, additional power scaling can be realized by combining several fiber disk lasers into a stack.

The spiral-coiled configuration is not the only possible; any other scheme of stacking of optical fibers with lateral delivery of pump also can be called fiber disk laser, even if the resulting shape of the device is not circular at all. (Similar situation takes place with disk lasers; they also have no need to be disk shaped.) In such a way, the fiber disk laser is rather concept of lateral delivery of pump to the active optical fiber that 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.