Optical fiber delivery of high peak power Nd:YAG Q-switched laser pulse is required for applications such as material
processing, medical or military. The maximal transmitting power is variously limited by optical breakdown of air in the
focal point and the damage threshold of fiber. A coupling system of 600μm all-silica optical fiber fused with taper fiber
coupler and 15MW, 8ns Nd:YAG laser pulses is presented, consisting of an inversed telescope and a taper fiber coupler
without the use of a vacuum chamber. The taper fiber delivers light basing on the principle of total reflection. The
influence of incidence angle and taper length on the reflection angle are theoretic analyzed based on geometric optics.
The coupling efficiency of the 12 tapered fibers fused with 1meter fiber is measured under different incidence angle of,
respectively, 20mrad, 40mrad and 60mrad. The experiment results show that the coupling efficiency decreases gradually
with the increase of taper length for larger modal loss. The larger incidence angle also decreases the coupling efficiency,
which is consistent with above theoretic analyze. For 20mrad incidence angle, the coupling efficiency reaches as
95.53%. No surface damage or bulk damage is observed for 20meters fiber. In conclusion, the system could transmit
15MW Nd:YAG laser pulses by 600μm all-silica optical fiber stably. Intensity of 600μm fiber output surface is
4.42GW/cm<sup>2</sup>. The simplified coupling system resolves air breakdown of focal area and surface damage of fiber surface.
This paper presents theoretical analysis and experiment results of four different fibers transmitting 10MW peak power Nd:YAG laser pulse. The main factors limiting to optical fiber transmission of high power laser pulse is pointed, including air breakdown at focus area and surface damage of optical fiber. The theory of air breakdown and the fiber coupling conditions is described briefly. The results of study to the transmission properties and damage conditions are presented on the basis of four different types of optical fibers. The results of the experiments are further analyzed in the aspects of transmitting efficiency, air breakdown and surface damage. The local and foreign optical fibers, with plastic-cladding and silica-cladding, and step- index and graded- index fibers are tested separately in the experiments. The experiments showed that the imported fibers are able to transmit up to 10MW peak power laser pulse with no any visible damage, while energy density at the fiber output end surface is 3.54GW/cm<sup>2</sup>. For local fibers, damage on the input surface of both plastic-cladding and silica-cladding, step-index fibers was found obviously. The column damage to the graded index fiber was also found and investigated in the research. Damage mechanisms of fiber at high peak power laser pulses are summarized. High quality finishing of fiber end surface will improve damage threshold tremendously. The conclusion of the study is that transmitting Q-switched Nd:YAG pulses of 10MW peak power is feasible for the domestically made fibers if their end surfaces are properly processed.