Give

Graduate Exam Abstract


Travis Day

M.S. Final
October 6, 2017, 3:00 pm - 5:00 pm
ERC Electronic Classroom (A210)
SiO2 Planarization: Impacts on High Energy Lasers and Thin-film Optical Properties

Abstract: The work of this
thesis is devoted to
examining the
impact of silicon
dioxide (silica or
SiO2)
planarization on the
optical properties
and laser damage
resistance of thin-
film coatings. SiO2
planarization is a
process to smooth
out fluence limiting
nodular defects
within multilayer
coatings for
high-energy laser
applications.
Mitigating these
defects will improve
the power handling
abilities and
improve the lifetime
of laser coatings.
Presented here is a
combination of work
with the aim of
evaluating the
optical and laser
damage
properties of SiO2
planarization within
single layers,
bilayers, and
multilayers. As
compared to control
(non-planarized)
samples, a 2-3x
increase in the thin-
film absorption,
which decreases
with post-process
annealing, was
discovered for SiO2
planarized samples.
This suggests that
planarization creates
oxygen
related defects which
can be annealed out
and little impurity
implantation.
Investigations of
laser damage
resistance were
carried out at λ =
1030nm and pulse
durations of Ï„ =
220ps and 9ps. The
laser damage of
single and bilayer
coatings is known to
be dependent on the
substrate-coating
interface and this is
further
evidenced within this
thesis. This is
because the effects
of planarization are
masked by the
extrinsic laser
damage processes
within the single and
bilayers. Slight
change (<15%) in
the laser induced
damage
threshold (LIDT) at
220ps and 9ps was
observed for
planarized single
and bilayers.
Depending on
coating
design, post-process
annealing was
shown to increase
the LIDT by ~10% to
~75% at 220ps and
~10% to
~45% at 9ps.
Although the fused
silica substrate
surface LIDT was
shown to follow the
√𝜏 pulse scaling
law for pulses above
~10ps, the single
and bilayer coatings
do not follow this
pulse scaling. The
divergence
iii

from the √𝜏 pulse
scaling on the
coatings suggests a
variation in the laser
damage initiation
mechanisms
between 220ps and
9ps.
Multilayer high-
reflecting (HR)
mirrors with varying
planarization design
were also damage
tested.
A 6-7 J/cm2 LIDT,
with 220ps, was
observed for HR
coatings with SiO2
planarization layers
within high
electric-field areas
within the coating.
However, SiO2
planarization at the
substrate-coating
interface,
where the electric-
field is minimal, and
control (non-
planarized) was
shown to have a
LIDT of 63 ± 1.2
J/cm2 and 21.5 ± 0.5
J/cm2 for 220ps,
respectively. At 9ps,
the LIDT varied less
than 90% difference
between the various
planarization
designs. The
substrate-coating
planarization
multilayer and
control
coating had an equal
LIDT of 9.6 ± .3
J/cm2 at 9ps. This
again suggests a
deviation in the laser
damage
mechanism between
220ps and 9ps and
each respective
coating design.


Adviser: Carmen Menoni
Co-Adviser: Mario Marconi
Non-ECE Member: John Williams
Member 3: N/A
Addional Members: N/A

Publications:
Day, T., et al. Impacts of SiO2 planarization on optical thin film properties and laser damage resistance. No. LLNL-PROC-713180. Lawrence Livermore National Laboratory (LLNL), Livermore, CA, 2016.


Program of Study:
ECE-546-001
MECH-567-001
ECE-506-001
ECE-507-001
ECE-574-001
ECE-404-001
ECE-673-001
ECE-441-001