The goal of this series of online meetings is to provide a forum for regular discussions between the teams that work on common design aspects of next-generation gravitational-wave detectors Einstein Telescope and Cosmic Explorer.
The plan is to have a meeting each 2-3 months and start with topics that are more urgent, i.e., that have a strong impact on the detector infrastructure including optical layout, stray-light noise, Newtonian noise, ...
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https://wiki.et-gw.eu/ISB/XGCD (accessible by ET collaboration members)
https://dcc.cosmicexplorer.org/cgi-bin/private/DocDB/DisplayMeeting?conferenceid=1056 (accessible by CE consortium members)
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XGCD Optical Design, Jan 22, 2024
Meeting Notes
85 participants + 7 (napoli group) = 92!!! (see screenshots at the bottom)
Intro slides (Lisa, Jan)
Common challenges in CE and ET, useful to discuss each other choices
Why not just scale up the LIGO optical design?
CE slides (Jon Richardson, Paul Fulda, Craig Cahillane for CE team)
Jon Richardson
There are a number of reasons why the LIGO optical design is inadequate.
One issue is optics size in the corner station and clipping loss. 40km CE has about 12cm beam radius. Needs about 70cm diameter ITMs. 500ppm SEC loss requirement. About 10kW PRC power.
LIGO TCS: CP+RH at ITM. Correct quadratic term in curvature with RH, but there are higher-order terms to be corrected. CP is meant to do it.
CP needs to be eliminated in the higher-power condition of future detectors like CE/ET. Plan is to demonstrate a new technology in LIGO A#.
Scattering into HOM by BS depends on angle of incidence (AOI). Can be as high as 100ppm. Low AOI is favored for TC of BS since it decreases divergence of MECH-x / SEC paths.
Paul Fulda (CE slides continued)
Starting with 450 arm-cavity finesse. High arm finesse would enhance SEC loss, degrade squeezing due to increased mode mismatch, and it poses additional challenges to short SEC scenarios.
CE HF response is impacted by second SEC resonance due to long arms, and this issue influences the optimal choice of SEC length. Short SEC is preferred from a detector response perspective, but makes it hard to accumulate Gouy phase and expand to a 12cm beam.
Several corner layouts are conceivable. Many of them were invented to reduce the AOI on the BS, no final decision yet, work in progress to downselect.
Jerome Degallaix for Einstein Telescope Optical Design Team
Arm cavity basic design already – reminder of parameters on page 3
Focus of current work is on recycling cavity design
Difference between ET-HF and ET-LF, this talk focuses on ET-HF
Status of design for recycling cavity – requirements on slide 9 and 10
Important requirement: BS not larger than aVirgo+
Page 12: design for ET-HF
Page 13: current ET-HF layout, 45 aoi on BS
Page 17 – work plan
Matt Evans: Is the power density on ZM2 a problem?
Matt Evans: Did your team confirm that having the BS in the telescope (i.e., highly curved wavefront) is ok? This is something we also worry about
Lisa Barsotti: not much on impact of 10 dB squeezing requirement in your talk. Is it because the impact of HOM resonance in the band is more important for CE, and not such a big deal for ET?
Jon Richardson: can you please clarify: in your case, your arm cavity design is basically done, correct?
Stefan Ballmer: What imposes the size limit on the BS? 2.3 cm – is thermo-refractive noise or something else?
Jerome: No, this noise is much smaller, this is motivated by thermal lensing inside the BS
Stefan Ballmer: do you have a good sense of tolerances and specification for a lens in Compensation Plates?
Paul Fulda: astigmatism in the recycling cavity – we worry a lot about this for CE for some of the designs. Are you considering more complex optics to compensate?
Jon Richardson: SEC loss —- 1000 ppm nominal design for ET, less stringent than 500 SEC for CE, although also 20kW in PRC which is higher than CE. Are you also worried about the AOI on the BS?
Matt Evans: AOI on BS – can you change your mind later on, or is it an infrastructure issue that you have to decide ASAP?
Jan Harms: Infrastructure considerations important for CE too, even if not underground, given how some of the corner layout options look like. How does the CE infrastructure look like for the corner? The corner station will be elevated somehow with respect to the ground? Is all going to be on one plane?
Stefan: We also haven’t thought about how our input optics connect to the recycling cavities and filter cavity. Still working on that – have you thought about that?
Lisa Barsotti: do people have concerns about low AOI on the Beam Splitter? Do people think it is a risky thing, and need some validation, or straightforward?
Stefan Hild – One topic if time permits: What is people’s take on tools. Is Zeemax the ultimate solution? Or would people be interested to have an OptoCAD successor / IfoCAD / or similar?
Lisa, Jan: Thank you all, good discussion, very useful for both teams, more of these meetings will happen! Stay tuned.
Participant screenshots:
DIGESTED LIST OF ACTION ITEMS
Cosmic Explorer action items: Notes from 4pm discussion (Kevin, Stefan)
Einstein Telescope action items (Lisa, please edit):
Common interests: