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High power Fiber Lasers
Hinke Schokker
Short History•First fiber laser in 1961 by
Elias Snitzer
•Unexplored
untill
late 1980’s
Impulse
from
telecommunications!
Before 1986…
After
1986!
E Snitzer, Phys. Review Letters 7,444 (1961)
Fiber lasers•
Thin
fiber with
glass
core doped
with
rare earth
elements•
Internal
reflection
•Fiber length: 1-100 m•Core diameter: 10-100 μm (human
hair
•Total diameter: 250 μm•Doping: , , 3Yb 3Er 3Nd
Cross section:
High power lasers: fibers & disksTwo solutions to the same problem
Long and thin
Or
fat and short
Increase surface to volume ratio to loose heat!
Ytterbium
•Inhomogenous
broadening•Broad
linewidth
•Emission
wavelength:1040 nm•Absorbtion
wavelength: 979 nm
•Low quantum
defect!•Maximum power 10 kW (CW)
Single vs Multimode
•Small core •Single transversal mode•Less power but betterbeam quality
•Large core ~ 62.5 µm•More transversal modes•More power, less beam quality
Some Applications
WeldingCutting Printing
Marking Stent
manufacture
Yb fiber laser Companies:•
IPG Photonics
•
V-gen•
TekhnoScan
•
Multiwave
Photonics•
Control
Micro Systems
•
Etc.
Advantages
•Heating is not a problem
•Beam quality much better
•Significantly better efficiency
•Flexibility, compact
•Stable and reliable,low maintenance, cheaper
Disadvantages
•Power: scalable
to high powers?
• Nonlinearities
Recent experiment•“Highly efficient cladding-pumped ytterbium-doped fiber laser using diode laser stack”• >2.1 kW (CW)•Slope efficiency 79 %•Beam quality factor 1.2•Power scalability: >10 kW possible!
“Multi-kilowatt Single- mode Ytterbium doped Large-core Fiber laser”, Yooncan
Jeong
et al., J. of
Opt. Society of Korea, 23 November 2009
Limitations•Thermal limits: rupture, melting, thermal lensing•Nonlinearities: Raman/Brillouin
scattering
•Optical damage•Pump power limits (diode pump laser, dopingconcentration)
Powers as high as 36.6 kW Possible!
Jay W. Dawson et al, “Analysis of the scalability of diffraction limited Fiber lasers and amplifiers to high averagePowers”, Opt. Express 16, 13240-13266 (2008)
Questions?
References•
www.gsiglasers.com
•
www.rp-photonics.com•
http://www.orc.soton.ac.uk
•
http://www.optics.rochester.edu•
http://en.wikipedia.org/wiki/Fiber_laser
•
Slope efficiency: product of the pump absorption efficiency, the
ratio of laser to pump photon energy (→ quantum defect), the quantum efficiency
of the
gain medium, and the output coupling efficiency of the laser resonator.•
Beam quality
•
Brillouin
scattering: From
a quantum
point of view, Brillouin
scattering
is an interaction
of light
photons
with
acoustic
or
vibrational
quanta
(phonons).
The interaction
consists
of an
inelastic
scattering
process
in which
a phonon or
magnon
is either
created
(Stokes
process) or
annihilated
(anti-Stokes
process). The energy
of the scattered
light
is slightly
changed.•
Raman
scattering: The nonlinear
response of a transparent
optical
medium
to the optical
intensity
of light
propagating
through
the medium is very
fast, but
not
instantaneous. In particular, a non-instantaneous
response is
caused
by
vibrations
of the crystal
(or
glass) lattice. When
these vibrations are associated
with
optical
phonons, the effect is called
Raman scattering,
Different transverse modes
"for groundbreaking achievements concerning the transmission of light in fibers for optical communication"
Nobelprize
in Physics
2009
Charles K. Kao½
of the prize
Characteristics•
Small
quantum
defect high slope
efficiency•
Inhomogeneous
broadening
•
Long lived
excited
state•
High doping density
possible
•
Linewidth•
Maximum power: 10 kW
•
Single/multimode
(transversal)•
Upper level lifetime: 800 μs
•
linewidth: ~6*10^16 Hz•
Several
longitudinal
modes