2021 Fiscal Year Annual Research Report
Exploring the hidden universe with enhanced broadband detection of neutron star gravitational waves
| Project/Area Number |
20F20713
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| Research Institution | National Astronomical Observatory of Japan |
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Principal Investigator |
麻生 洋一 国立天文台, 重力波プロジェクト, 准教授 (10568174)
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| Co-Investigator(Kenkyū-buntansha) |
PAGE MICHAEL 国立天文台, 重力波プロジェクト, 外国人特別研究員
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| Project Period (FY) |
2020-11-13 – 2023-03-31
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| Keywords | Gravitational Wave / Squeezing |
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| Outline of Annual Research Achievements |
At the TAMA300 test facility we have demonstrated improvement of the automated alignment and control system of the Fabry-Perot filter cavity that is used to provide frequency dependent squeezed light to gravitational wave detectors. Any small fluctuations in the squeezed light path will have a detrimental effect on the sensitivity of a gravitational wave detector. We have improved low frequency noise performance of a wide bandwidth control beam, which will ease commissioning of frequency dependent squeezing.
We have also performed a design study on the integration of the filter cavity into the main KAGRA detector. We have assessed the effect of backscattered light on the overall squeezing improvement. Stray light that leaks from the interferometer will be back-reflected from squeezer optics with a phase disturbance characteristic of the residual seismic motion. This effect is significant even when the amount of incident stray light is of the order of nanowatts. We have made an initial estimate that single stage suspensions may be possible for the KAGRA filter cavity, given reduced seismic noise at the underground site. Simpler suspensions would be a great boon to easier commissioning.
Some efforts have been made in preparing KAGRA for the next observing run, including cleaning and absorption measurement of a KAGRA test mass, and introduction of the noise budgeting for the multi-stage suspensions of the detector mirrors.
In November 2021 Page presented NAOJ research activities to Suwa Seiryou High School in Nagano as part of the JSPS Science Dialogue program.
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| Current Status of Research Progress |
Current Status of Research Progress
2: Research has progressed on the whole more than it was originally planned.
Reason
We are preparing a publication regarding monochromatic control of the filter cavity. Currently, we control the position of the cavity mirrors using a green beam that is frequency doubled from the main squeezed beam. While the green beam has large bandwidth and is easy to align and control, it is not inherently co-propagating with the squeezed beam. Demonstrating the feasibility of a co-propagating control beam at the same wavelength allows us to reduce control noise, which is very important for the low frequency sensitivity of KAGRA.
The TAMA laboratory is undergoing a few important technical upgrades. First, we aim to improve the optical loss, since this is one of the main causes of degradation of squeezing. Specifically, we are working on replacing the optical parametric oscillator that generates squeezed vacuum, and an in-vacuum optical isolator which prevents backscattered light from interfering with the measurement. Second, we are also upgrading the digital control and data acquisition system. One of the key functions of this system is to synchronize signals between devices separated by long distance. Gaining experience in automated control and high speed data archiving will be important when integrating the filter cavity into the equivalent architecture of KAGRA.
Design of the KAGRA filter cavity is currently focused on determining the amount of suspension required for critical components. Multi-stage suspensions can greatly reduce detrimental back-scattered light, but are also much more complex to commission and keep aligned.
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| Strategy for Future Research Activity |
Replacing limiting sources of optical loss will allow us to investigate other sources of degradation of frequency dependent squeezing, in particular optical backscattering, phase noise and mode matching loss.
We have several ideas for future major upgrades to the TAMA facility. Propositions include testing internally generated squeezing or using a filter cavity with three mirrors. The NAOJ gravitational waves group is holding a strategy meeting to discuss, among other things, the most relevant and impactful use of the TAMA facility for the foreseeable future.
Construction of the filter cavity at the actual KAGRA facility is expected to be done in a modular fashion. A priority in the design of the filter cavity will be to easily switch from the simpler frequency independent squeezing setup to the frequency dependent setup incorporating the filter cavity. The Kamioka mine presents an advantage with respect to its low seismic noise, but also the challenge of limited space.
KAGRA is entering a critical period of its commissioning phase with the lead-up to the LIGO-Virgo-KAGRA collaboration Observing Run 4. We anticipate participating in some of the commissioning activities remotely in Tokyo and onsite in Kamioka. In particular, there will be a lot of work related to the controls of the test mass suspensions, which are a problematic source of low frequency noise. Noise budgeting of the suspension controls can be performed remotely, so this is also convenient for our schedule.
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