Walter Scott, Jr. College of Engineering

Graduate Exam Abstract

Drew Schiltz
M.S. Final
Apr 30, 2015, 3:00 pm - 5:00 pm
ERC A210 (Foothills Campus)
Abstract: The work presented in this thesis is
dedicated toward investigating, and
ultimately improving the laser damage
resistance of ion beam sputtered
interference coatings. Not only are
interference coatings a key
component of the modern day laser,
but they also limit energy output due
to their susceptibility to laser induced
damage. Thus, advancements in the
fluence handling capabilities of
interference coatings will enable
increased energy output of high
energy laser systems.
Design strategies aimed at improving
the laser damage resistance of
Ta2O5/SiO2 high reflectors for
operation at one micron wavelengths
and pulse durations of several
nanoseconds to a fraction of a
nanosecond are presented. These
modified designs are formulated to
reduce effects from the standing wave
electric field distribution in the coating.
Design modifications from a standard
quarter wave stack structure include
increasing the thickness of SiO2 top
layers and reducing the Ta2O5
thickness in favor of SiO2 in the top
four bi-layers. The coating structures
were deposited with ion beam
sputtering. The modified designs
exhibit improved performance when
irradiated with 4 ns duration pulses,
but little effect at 0.19 ns. Scaling
between the results from testing at
these two pulse durations shows
deviation from Ï„1/2 scaling, where Ï„ is
the pulse duration. This suggests
possible differences in the initial
damage mechanism. Also presented
are results for at-wavelength optical
absorption losses measured with
photothermal common-path
interferometry and surface roughness
measurements with atomic force
Further studies on the damage
thresholds of interference coatings
operating at 1.6 micron wavelength
and 2 picosecond pulse durations are
presented. High reflection and anti-
reflection coating structures were
fabricated with varied high index
materials: HfO2, Y2O3 and Ta2O5.
For damage testing, an optical
parametric chirped pulse amplifier
was fabricated and implemented.
This source is capable of producing
~5 millijoule pulses with a tunable
wavelength between 1.5 and 2
micron. When investigated at 1.6
micron wavelength, the interference
coatings exhibit ultra-low absorption
losses and damage thresholds at ~7.0
J/cm2 and 3.5 TW/cm2 peak
intensities, near that of the infrared
grade fused silica substrates they are
deposited on. Furthermore,
interference effects and lower band
gap materials do not impair the
damage threshold. This behavior is
significantly different than what has
previously been observed at similar
pulse durations and more common
laser wavelengths around 0.8 to 1
micron. I show that conventional rate
equation modeling proves inadequate
at describing the obtained results.
Adviser: Carmen Menoni
Co-Adviser: N/A
Non-ECE Member: Mark Bradley, Physics
Member 3: Mario Marconi, ECE
Addional Members: N/A
D. Schiltz, D. Patel, L. Emmert, C. Baumgarten, B. Reagan, W. Rudolph, J. Rocca, and C. Menoni, "Modification of multilayer mirror top-layer design for increased laser damage resistance," in SPIE Laser Damage(International Society for Optics and Photonics), pp. 92371G-92371G-92377 (2014).

P. Langston, E. Krous, D. Schiltz, D. Patel, L. Emmert, A. Markosyan, B. Reagan, K. Wernsing, Y. Xu, and Z. Sun, "Point defects in Sc 2 O 3 thin films by ion beam sputtering," Applied optics 53, A276-A280 (2014).

D. Patel, D. Schiltz, P. Langton, L. Emmert, L. Acquaroli, C. Baumgarten, B. Reagan, J. Rocca, W. Rudolph, and A. Markosyan, "Improvements in the laser damage behavior of Ta2O5/SiO2 interference coatings by modification of the top layer design," in SPIE Laser Damage(International Society for Optics and Photonics), pp. 888522-888522-888525 (2013).

Program of Study:
ECE 404
ECE 441
ECE 505
ECE 506
ECE 546
ECE 580 (A9,B1,B2)
ECE 673