We demonstrated growth of YAG, LuAG and CALGO single crystal fibers with doping Nd, Yb, Er, and Ce by the
micro-pulling-down technique. Those fibers have applications in high power lasers and scintillating detectors. For laser
operation, average power of 65 W energy of 4 mJ and peak power above 7 MW have been demonstrated in various
configurations. Those results push the limits of end-pumped bulk crystals in terms of average power and exceed the
limits of pulsed fibers lasers in terms of energy. For scintillating applications, high density/high light yield detectors are
developed for nuclear science and medical applications.
Recent developments of the micro-pulling down technique lead to efficient laser demonstration with Nd:YAG single
crystal fibers. Indeed these media which benefit from the spectroscopic and thermal properties of bulk crystals and from
the thin and long shape of glass fibers are ideal candidates for high average and high peak power laser systems. In this
work, we investigate the potential of Yb:YAG single crystal fibers. After a careful design taking into account the quasithree
level structure of the Yb3+ ions, we grew single crystal fibers by the micro-pulling down technique. With a 1 at.%
doped and 40 mm long single crystal fiber of 1 mm in diameter, we obtained a power of 50 W in CW operation under
200 W of incident pump power. In the Q-switched regime, we achieved pulses with an energy of 1.8 mJ at 5 kHz and a
duration of 13 ns for 120 W of pump power. We measured a M² value below 2.5. We also investigated the thermal
management of our system by the use of thermal cartography and Finite Element Analysis, showing a maximum
temperature smaller than 120°C reached on the pumped end face for 200 W of pump power. These results are a very
promising to design high average power and high peak power laser sources.
We designed single-crystal fibers to combine excellent spectroscopic and thermo-mechanical properties of bulk crystals
and ability of pump guiding and good heat repartition of doped glass fibers. Such single-crystal fibers of excellent optical
quality were grown by the micro-pulling-down technique. A remarkable advantage of this technique is that pump
guiding is achieved in the directly grown fiber without additional polishing on the cylinder. We designed 0.2%-Nd doped
YAG crystal fibers sample of 50 mm and 1 mm diameter and AR coated on both end faces. It was longitudinally pumped
by a fiber-coupled laser diode with a maximum output power of 120 W at 808 nm. Laser emission at 1064 nm was
achieved inside a two concave mirrors cavity. We obtained 20 W of laser emission with a M2 quality factor of 6, for an
incident pump power of 120 W and a slope efficiency of 18% without any thermal management problems. Besides, a
power of 16 W with linearly polarized laser emission has been obtained under the same pump power by introducing a
thin plate polarizer in the cavity. An acousto-optical modulator was inserted inside the cavity and 360 kW of peak power
with 12 ns pulses at 1 kHz repetition rate were achieved under 60 W of pump power. This work shows real
improvements of laser performances in directly grown single crystal fibers. A complete thermal study confirms a good
heat management and demonstrates scalability to high average power laser sources.
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