The amount of laser power that a fiber is transmitting without damage is specified as the power output of the laser divided by the area of the laser spot,

where w is the beam radius of the laser beam at distance L from the fiber surface. The radius w is given by:

When the position of w₀, the focal waist, is inside an optical fiber of index n, then the Rayleigh range parameter z₀ is given by:

The output of a pulsed laser, typically specified in millijoules (mJ) of energy per pulse, must first be converted to the power per pulse. For example, a pulsed laser that produces 50mJ in a 10ns pulse produces an output power of 5MW.

For a Nd:YAG laser (1064nm) emitting 10ns pulses, synthetic fused silica fibers have survived pulse energies up to 0.4 - 0.6 Giga-Watts/cm².

To achieve maximum power transmission the end face of the fiber must be optically smooth and perpendicular to the beam. The beam must be focussed properly to prevent light from leaking into the cladding or else the polymer cladding or buffer coating may be damaged. The epoxy used for bonding the fiber to the connector can be affected as well. For this reason, a silica/silica fiber is often used in a specially designed mounting or connector to better tolerate the high power densities and rapid heating levels. It is also recommended that the beam fill no more than 70% of the core diameter.

Configurations that help spread or reduce the energy density at the fiber surfaces have helped reduce laser damage at high energy levels. Options such as tapered end-tips, spheres, and other shaped end tips manufactured onto the end of the fiber are additional options offered by Polymicro. Some of the many possible configurations are shown and discussed in the Fused Silica Micro-Components chapter.

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