High Power Fiber Lasers refers to the laser using rare earth element doped glass fiber as the gain medium.
Among them,ytterbium doped fiber is one of the most core devices of high-power ytterbium doped fiber laser system.
However with the increase of the output power of fiber laser various stability“killers" such
as transverse mode instability(TMIStimulated Raman scattering(SRphenomenon and thermal damage have surfaced.
Fiber laser is mainly composed of pump source,gain medium(active fiberand resonator.
Principle of fiber laser with resonant cavity structure: the power of pumping
semiconductor laser LD is injected into ytterbium doped double clad fiber(YDF)through fiber grating (high emission grating HR and ow reflection grating OC)through forward and backward beam combiners.
After the rare earth ions in YDF absorb the pump lightthe particle number inversion distribution is formed to generate spontaneous emission light.
Then, under the action of fiber grating pair(hr-oc)the stimulated emission light is formed to amplify and generate laser light which is output through C and output optical cable QBH.
Amplifier structure fiber laser principle: similar to the resonant cavitythe difference is
that the seed source laser at the front stage reduces the power requirements of the system on the unit devices.
And higher power can be obtained
TMI effect of lateral mode instability
Lateral mode instability refers to the sudden change of high-power fiber laser from steady state fundamental mode output to non steady-state hiah-order mode output as the output
power increases or exceeds a certain time after reaching a certain threshola. which wil
lead to the decline of beam quality and limit the increase of fiber laser output power.
In serious cases the laser which is called“the fastest knifethe most accurate ruler and the brightest light" will not live up to its name.
