Laser Focus World - January 2015

Hackensack, NJ 07601 USA ∙ + 1.201.343.8983 ∙ main@masterbond.com

Ideal for
spin coating

Thermally stable

Tg of 120°C Low viscosity 70-120 cps

Very low shrinkage upon cure

1-2%

Outstanding optical clarity

Refractive Index

1.517

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January 2015 www.laserfocusworld.com Laser Focus World 14

Thulium-based 2 µm fiber laser reaches
200 MW peak power

Lasers emitting at around 2 µm are
useful for their eye-safe qualities (re-
mote sensing) and other purpos-
es (IR spectroscopy, supercontinuum
generation, and materials process-
ing); as for almost any other laser-
emission wavelength, scientists and
engineers using these lasers are of-
ten looking for more laser power
and or pulse energy at 2 µm. A team
from Friedrich-Schiller-Universität
Jena and the Fraunhofer Institute for
Applied Optics and Precision Engi-
neering (both in Jena, Germany) has
helped to fulfil these needs by de-
veloping a thulium (Tm)-based fiber-
laser system that produces a peak
pulse power of more than 200 MW,
The chirped-pulse-amplification
(CPA) system includes a Tm-doped fi-
ber with a mode-field diameter of 65
µm, efficient dielectric gratings, and
a Tm-based fiber oscillator. The fi-
ber oscillator, which operates in the
stretched-pulse regime and emits 1. 2
nJ pulses at a 24 MHz repetition rate,
accomplishes stable mode-locking by
taking advantage of nonlinear polar-
ization changes; it is a self-starting
oscillator relying on a saturable-ab-
sorber mirror. The stretcher and com-
pressor are enclosed in low-humidity
boxes to minimize light loss from wa-
ter-absorption lines; the compressor
gratings have a diffraction efficien-
cy of more than 98% and a compres-
sor efficiency of more than 80%. The
large-pitch-fiber amplifier is direct-
ly water-cooled and counter-pumped
with light from a 790 nm laser diode.
Future use of a vacuum or nitrogen
atmosphere in various parts of the
optical path could reduce thermal-
ly induced beam degradation as well
as nonlinear effects; larger mode-
field areas will lead to even higher
powers. Reference: Fabian Stutzki et
al., Opt. Lett. (2015); http://dx.doi.
org/10.1364/OL. 40.000009.