| NSF Org: |
PHY Division Of Physics |
| Recipient: |
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| Initial Amendment Date: | June 23, 2014 |
| Latest Amendment Date: | July 6, 2016 |
| Award Number: | 1404110 |
| Award Instrument: | Continuing Grant |
| Program Manager: |
Pedro Marronetti
pmarrone@nsf.gov (703)292-7372 PHY Division Of Physics MPS Directorate for Mathematical and Physical Sciences |
| Start Date: | September 1, 2014 |
| End Date: | August 31, 2018 (Estimated) |
| Total Intended Award Amount: | $315,000.00 |
| Total Awarded Amount to Date: | $315,000.00 |
| Funds Obligated to Date: |
FY 2015 = $105,000.00 FY 2016 = $105,000.00 |
| History of Investigator: |
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| Recipient Sponsored Research Office: |
1523 UNION RD RM 207 GAINESVILLE FL US 32611-1941 (352)392-3516 |
| Sponsor Congressional District: |
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| Primary Place of Performance: |
Gainesville FL US 32611-2002 |
| Primary Place of
Performance Congressional District: |
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| Unique Entity Identifier (UEI): |
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| Parent UEI: |
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| NSF Program(s): |
LIGO RESEARCH SUPPORT, CONDENSED MATTER & MAT THEORY |
| Primary Program Source: |
01001516DB NSF RESEARCH & RELATED ACTIVIT 01001617DB NSF RESEARCH & RELATED ACTIVIT |
| Program Reference Code(s): |
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| Program Element Code(s): |
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| Award Agency Code: | 4900 |
| Fund Agency Code: | 4900 |
| Assistance Listing Number(s): | 47.049 |
ABSTRACT
The research project is a computational oriented theoretical effort that aims at understanding the physical origin of thermal noise in optical coating materials at the atomic level and providing guidance for the optimal ratio of metallic elements in composite amorphous oxides (silica, titania, tantala, hafnia etc). Thermal noise that is caused by atomic movement at finite temperature affects the performance of ultra high-resolution interferometers such as the laser interferometer employed in the Laser Interferometer Gravitational-Wave Observatory (LIGO) and is of special interest to the LIGO Scientific Collaboration (LSC). The project will provide rigorous training for graduate students in computational physics. The PI has collaborations with a number of international experimental and computational materials physics groups including a group at Glasgow UK, ETH Zurich, and a group at Fudan University Shanghai. She also visits Colombi at the Institute of Astrophysics Paris to discuss issues regarding large-structure simulations. The LSC is an international organization. It also has a tight relation with other organizations that focus on gravitational wave observations. The optical group organizes focus sessions at LIGO meetings jointly with other gravitational organizations (VIRGO, AGO etc.) and in independent workshops.
Advanced LIGO, the major upgrade of LIGO, is expected to be limited by thermal noise in the most critical ~50-150 Hz frequency band while the performance of several state-of-the art frequency stabilization systems is limited by thermal noise at frequencies as low as a few Hz. This project also studies mechanical properties of crystalline materials (GaAs/AlGaAs, and GaP/AlGaP), a new paradigm for optical coating that has been demonstrated experimentally. Improving dielectric coatings and reducing thermal noise have applications in many high precision optical measurements far beyond LIGO, such as time and frequency measurements, measurements of the equivalence principle, and many others. The computational approach of characterizing amorphous materials will also be useful to many other areas such as nano-scale science, materials science, and bio-science.
PUBLICATIONS PRODUCED AS A RESULT OF THIS RESEARCH
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PROJECT OUTCOMES REPORT
Disclaimer
This Project Outcomes Report for the General Public is displayed verbatim as submitted by the Principal Investigator (PI) for this award. Any opinions, findings, and conclusions or recommendations expressed in this Report are those of the PI and do not necessarily reflect the views of the National Science Foundation; NSF has not approved or endorsed its content.
Over the last four years we have made vast improvements to our ability to identify and use two level systems, figure 1, to calculate mechanical properties, including the all-important mechanical loss. The accuracy of mechanical loss calculations is important to the scientific community at large but more specifically, it is important to the Laser Interferometer Gravitational-Wave Observatory experiment. The experiment relies on amorphous coatings, whose thermal noise currently limits the precision in which gravitational waves can be detected [1]. By measuring the mechanical loss of different materials, we can help experimentalists choose what coatings should be investigated next and what generative techniques should be used.
In the process of helping LIGO experimentalist, we made great insights into the process of calculating mechanical loss. We have shown that an increase in the percentage of Ti in Ti doped Ta2O5 consistently decreases the mechanical loss at both low and room temperature, figure 2, due to increasing the Young's modulus, figure 3, while also decreasing the strain coupling constant, figure 4 [2].
We have also shown that using an uncorrelated TLS distribution is not sufficient to calculate the mechanical loss at high temperatures. [3] This discovery is important, since any other researchers interested in calculating mechanical loss at high temperatures will need to use a correlated distribution as well. We also then used this information to reproduce and uncover the physical mechanisms for a second peak observed in the measurements of ion-beam sputter amorphous silica [3].
We also studied the two-level system distribution, figure 5, and mechanical loss of amorphous Nb2O5. Not only is knowing the mechanical loss of Nb2O5 important to experimentalists, but in the process, we have created a potential function that can be used in molecular dynamics simulating software. This will allow us to perform more studies on the materials and allow other computational physicists to perform their own simulations on the materials as well.
We have performed many experiments and tests on ZrO2-doped Ta2O5. We have seen that when compared to the mechanical loss curves of pure Ta2O5, ZrO2-doped Ta2O5 has more broad loss peaks. We have also investigated many different Reverse Monte Carlo techniques using the experimental pair correlation function from our Stanford colleagues as our matching reference. Using these techniques, we have been able to accurately capture the slight differences between as-deposited and 800-degree Celsius annealed ZrO2-doped Ta2O5. We then characterized the angular distribution as well as other structural properties of these models. These structural properties are useful in our endeavor to create better potential functions for simulating these materials and achieving even more accurate mechanical loss calculations.
[1] G. M. Harry, A. M. Gretarsson, P. R. Saulson, S. E. Kittelberger, S. D. Penn, W. J. Startin, S. Rowan, M. M. Fejer, D. Crooks, G. Cagnoli et al., Classic. Quantum Gravity 19, 897 (2002).
[2] J. P. Trinastic, R. Hamdan, C. Billman, and H.-P. Cheng, Phys. Rev. B 93, 014015 (2016)
[3] Chris R. Billman, Jonathan P. Trinastic, Dustin J. Davis, Rashid Hamdan, and Hai-Ping Cheng, Phys. Rev. B 95, 014109 (2017)
Last Modified: 12/29/2018
Modified by: Hai-Ping Cheng
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