Editing LIGO (section)

==Future==

===LIGO-India===
{{Main|INDIGO}}
[[LIGO-India]], or INDIGO, is a planned collaborative project between the LIGO Laboratory and the Indian Initiative in Gravitational-wave Observations (IndIGO) to create a gravitational-wave detector in India.  The LIGO Laboratory, in collaboration with the [[National Science Foundation|US National Science Foundation]] and Advanced LIGO partners from the U.K., Germany and Australia, has offered to provide all of the designs and hardware for one of the three planned Advanced LIGO detectors to be installed, commissioned, and operated by an Indian team of scientists in a facility to be built in India.

The LIGO-India project is a collaboration between LIGO Laboratory and the LIGO-India consortium: Institute of Plasma Research, Gandhinagar; IUCAA (Inter-University Centre for Astronomy and Astrophysics), Pune and Raja Ramanna Centre for Advanced Technology, Indore.

The expansion of worldwide activities in gravitational-wave detection to produce an effective global network has been a goal of LIGO for many years. In 2010, a developmental roadmap<ref name="gwic2010">{{cite web |title=The future of gravitational wave astronomy |url=https://gwic.ligo.org/roadmap/Roadmap_100814.pdf |publisher=Gravitational Waves International Committee |access-date=3 September 2018 |archive-date=30 July 2017 |archive-url=https://web.archive.org/web/20170730062043/https://gwic.ligo.org/roadmap/Roadmap_100814.pdf |url-status=dead }}</ref> issued by the [[Gravitational Wave International Committee|Gravitational Wave International Committee (GWIC)]] recommended that an expansion of the global array of interferometric detectors be pursued as a highest priority. Such a network would afford astrophysicists with more robust search capabilities and higher scientific yields. The current agreement between the LIGO Scientific Collaboration and the Virgo collaboration links three detectors of comparable sensitivity and forms the core of this international network. Studies indicate that the localization of sources by a network that includes a detector in India would provide significant improvements.<ref>{{Citation |url=https://dcc.ligo.org/cgi-bin/DocDB/ShowDocument?docid=90988 |title=Improved Source Localization with LIGO India |journal=Journal of Physics: Conference Series |volume=484 |issue=1 |pages=012007 |date=28 September 2012 |first=Stephen |last=Fairhurst |id=LIGO document P1200054-v6|bibcode=2014JPhCS.484a2007F |arxiv=1205.6611 |doi=10.1088/1742-6596/484/1/012007 |s2cid=118583506 }}</ref><ref>{{Citation |arxiv=1102.5421 |title=Networks of Gravitational Wave Detectors and Three Figures of Merit |journal=Classical and Quantum Gravity |volume=28 |issue=12 |pages=125023 |date=25 April 2011 |first=Bernard F. |last=Schutz|bibcode = 2011CQGra..28l5023S |doi = 10.1088/0264-9381/28/12/125023 |s2cid=119247573 }}</ref> Improvements in localization averages are predicted to be approximately an order of magnitude, with substantially larger improvements in certain regions of the sky.

The [[National Science Foundation|NSF]] was willing to permit this relocation, and its consequent schedule delays, as long as it did not increase the LIGO budget.  Thus, all costs required to build a laboratory equivalent to the LIGO sites to house the detector would have to be borne by the host country.<ref>{{Citation |url=http://www.gravitycentre.com.au/wp-content/uploads/2009/10/Science-article-about-LIGO-Australia.pdf |title=U.S. Physicists Eye Australia for New Site of Gravitational-Wave Detector |journal=Science |volume=329 |issue=5995 |page=1003 |first=Adrian |last=Cho |date=27 August 2010 |doi=10.1126/science.329.5995.1003 |bibcode=2010Sci...329.1003C |pmid=20798288 |url-status=dead |archive-url=https://web.archive.org/web/20130411020012/http://www.gravitycentre.com.au/wp-content/uploads/2009/10/Science-article-about-LIGO-Australia.pdf |archive-date=11 April 2013  }}</ref> The first potential distant location was at [[AIGO]] in [[Western Australia]],<ref>{{Citation |url=https://dcc.ligo.org/LIGO-T1000251/public |title=Report of the Committee to Compare the Scientific Cases for AHLV and HHLV |date=13 May 2010 |id=LIGO document T1000251-v1 |first1=Sam |last1=Finn |first2=Peter |last2=Fritschel |first3=Sergey |last3=Klimenko |first4=Fred |last4=Raab |first5=B. |last5=Sathyaprakash |first6=Peter |last6=Saulson |first7=Rainer |last7=Weiss}}</ref> however the Australian government was unwilling to commit funding by 1 October 2011 deadline.

A location in India was discussed at a Joint Commission meeting between India and the US in June 2012.<ref>[https://2009-2017.state.gov/r/pa/prs/ps/2012/06/192271.htm U.S.-India Bilateral Cooperation on Science and Technology] meeting fact sheet&nbsp;– dated 13 June 2012.</ref> In parallel, the proposal was evaluated by LIGO's funding agency, the NSF.  As the basis of the LIGO-India project entails the transfer of one of LIGO's detectors to India, the plan would affect work and scheduling on the Advanced LIGO upgrades already underway.  In August 2012, the U.S. National Science Board approved the LIGO Laboratory's request to modify the scope of Advanced LIGO by not installing the Hanford "H2" interferometer, and to prepare it instead for storage in anticipation of sending it to LIGO-India.<ref>[https://www.nsf.gov/nsb/meetings/2012/0823/major_actions.pdf Memorandum to Members and Consultants of the National Science Board]&nbsp;– dated 24 August 2012</ref> In India, the project was presented to the [[Department of Atomic Energy]] and the [[Department of Science and Technology (India)|Department of Science and Technology]] for approval and funding. On 17 February 2016, less than a week after LIGO's landmark announcement about the detection of gravitational waves, Indian Prime Minister [[Narendra Modi]] announced that the Cabinet has granted 'in-principle' approval to the LIGO-India mega science proposal.<ref>{{cite tweet |user=PMOIndia |author=Office of the Prime Minister of India |number=699931256008511492 |title=Cabinet has granted 'in-principle' approval to the LIGO-India mega science proposal for research on gravitational waves. |date=17 February 2016}}</ref>

A site near pilgrimage site of [[Aundha Nagnath]] in the [[Hingoli district]] of state [[Maharashtra]] in [[western India]] has been selected.<ref>{{cite news |title=First LIGO Lab Outside US To Come Up In Maharashtra's Hingoli |url=http://www.ndtv.com/india-news/first-ligo-lab-outside-us-to-come-up-in-maharashtras-hingoli-1456355 |date=8 September 2016 |journal=[[NDTV]]}}</ref><ref>{{Cite web|url=https://www.iucaa.in/~li_events/limma_2019/Day3_LIProj_Souradeep_LIMMA2019.pdf|title=LIGO-India: Origins & site search|last=Souradeep|first=Tarun|date=18 January 2019|page=27|url-status=live|archive-url=https://web.archive.org/web/20190915091406/https://www.iucaa.in/~li_events/limma_2019/Day3_LIProj_Souradeep_LIMMA2019.pdf|archive-date=15 September 2019|access-date=15 September 2019}}</ref>

On 7 April 2023, the LIGO-India project was approved by the Cabinet of Government of India. Construction is to begin in Maharashtra's Hingoli district at a cost of INR 2600 [[crore]]s.<ref name="approval">{{Cite news|url=https://timesofindia.indiatimes.com/india/cabinet-clears-rs-2600-crore-ligo-india-observatory-to-come-up-in-maharashtra-will-be-part-of-global-network/articleshow/99309532.cms|title = Cabinet clears Rs 2,600-crore LIGO-India; Observatory to come up in Maharashtra, will be part of global network| newspaper=The Times of India |date = 7 April 2023}}</ref>

===A+===
Like Enhanced LIGO, certain improvements will be retrofitted to the existing Advanced LIGO instrument. These are referred to as {{em|A+}} proposals, and are planned for installation starting from 2019 until the upgraded detector is operational in 2024.<ref>{{Cite web|url=https://www.nsf.gov/news/news_summ.jsp?cntn_id=297414|title=Upgraded LIGO to search for universe's most extreme events|website=www.nsf.gov|date=14 February 2019 |language=en|access-date=2020-04-09}}</ref> The changes would almost double Advanced LIGO's sensitivity,<ref>{{Cite journal |title=Prospects for doubling the range of Advanced LIGO |journal=Physical Review D |volume=91 |issue=62005 |pages=062005 |date=16 March 2015 |first1=John |last1=Miller |first2=Lisa |last2=Barsotti |author-link2=Lisa Barsotti|first3=Salvatore |last3=Vitale |first4=Peter |last4=Fritschel |first5=Matthew |last5=Evans |first6=Daniel |last6=Sigg |doi=10.1103/PhysRevD.91.062005 |arxiv=1410.5882 |url=http://dspace.mit.edu/bitstream/handle/1721.1/96149/PhysRevD.91.062005.pdf|bibcode=2015PhRvD..91f2005M |s2cid=18460400 }}</ref><ref>{{cite conference |title=Getting an A+: Enhancing Advanced LIGO |first=Michael E. |last=Zucker |url=https://dcc.ligo.org/LIGO-G1601435/public |id=LIGO-G1601435-v3 |date=7 July 2016 |conference=LIGO–DAWN Workshop II |conference-url=https://wiki.ligo.org/LSC/LIGOworkshop2016/WebHome}}</ref> and increase the volume of space searched by a factor of seven.<ref>{{Cite web|url=https://www.popularmechanics.com/space/telescopes/a26362135/ligo-gravitational-wave-observatory-update/|title=LIGO Gravitational Wave Observatory Getting $30 Million Upgrade|last=Thompson|first=Avery|website=www.popularmechanics.com|language=en-US|access-date=17 February 2019|date=15 February 2019}}</ref> The upgrades include:
* Improvements to the mirror suspension system.<ref>{{Cite news|url=https://www.bbc.com/news/science-environment-47213202|title=Black hole detectors to get big upgrade|last=Ghosh|first=Pallab|date=15 February 2019|access-date=17 February 2019|language=en-GB}}</ref>
* Increased reflectivity of the mirrors.
* Using frequency-dependent [[squeezed light]], which would simultaneously decrease [[radiation pressure]] at low frequencies and [[shot noise]] at high frequencies, and
* Improved [[Optical coating|mirror coatings]] with lower mechanical loss.<ref>{{Cite web|url=https://dcc.ligo.org/LIGO-T1800042/public|title=LIGO-T1800042-v5: The A+ design curve|website=dcc.ligo.org|access-date=2020-04-09}}</ref>

Because the final LIGO output photodetector is sensitive to phase, and not amplitude, it is possible to squeeze the signal so there is less [[phase noise]] and more amplitude noise, without violating the [[Uncertainty principle|quantum mechanical limit]] on their product.<ref>{{Cite web|title=The Quantum Enhanced LIGO Detector Sets New Sensitivity Record |url=http://ligo.org/science/Publication-SqueezedVacuum/index.php}}</ref> This is done by injecting a "squeezed vacuum state" into the dark port (interferometer output) which is quieter, in the relevant parameter, than simple darkness. Such a squeezing upgrade was installed at both LIGO sites prior to the third observing run.<ref>{{Cite journal|last1=Tse|first1=M.|last2=Yu|first2=Haocun|last3=Kijbunchoo|first3=N.|last4=Fernandez-Galiana|first4=A.|last5=Dupej|first5=P.|last6=Barsotti|first6=L.|author-link6=Lisa Barsotti|last7=Blair|first7=C. D.|last8=Brown|first8=D. D.|last9=Dwyer|first9=S. E.|last10=Effler|first10=A.|last11=Evans|first11=M.|date=2019-12-05|title=Quantum-Enhanced Advanced LIGO Detectors in the Era of Gravitational-Wave Astronomy|journal=Physical Review Letters|volume=123|issue=23|pages=231107|doi=10.1103/PhysRevLett.123.231107|pmid=31868462|bibcode=2019PhRvL.123w1107T|doi-access=free|hdl=1721.1/136579.2|hdl-access=free}}</ref> The A+ improvement will see the installation of an additional [[optical cavity]] that acts to rotate the squeezing quadrature from phase-squeezed at high frequencies (above 50&nbsp;Hz) to amplitude-squeezed at low frequencies, thereby also mitigating low-frequency [[radiation pressure]] noise.

===LIGO Voyager===
A third-generation detector at the existing LIGO sites is being planned under the name "LIGO Voyager" to improve the sensitivity by an additional factor of two, and halve the low-frequency cutoff to 10&nbsp;Hz.<ref name="ISWP15">{{Cite report|url=https://dcc.ligo.org/LIGO-T1500290/public|title=Instrument Science White Paper|last1=McClelland|first1=David|last2=Evans|first2=Matthew|date=8 October 2015|publisher=LIGO Scientific Collaboration|id=LIGO Document T1500290-v2|last3=Lantz|first3=Brian|last4=Martin|first4=Ian|last5=Quetschke|first5=Volker|last6=Schnabel|first6=Roman}}</ref> Plans call for the glass mirrors and [[Nd:YAG laser|1064&nbsp;nm lasers]] to be replaced by even larger 160&nbsp;kg silicon test masses, cooled to 123&nbsp;K (a temperature achievable with [[liquid nitrogen]]), and a change to a longer laser wavelength in the 1500–2200&nbsp;nm range at which silicon is transparent. (Many documents assume a wavelength of 1550&nbsp;nm, but this is not final.)

Voyager would be an upgrade to A+, to be operational around 2027–2028.<ref>{{cite tech report |author=LIGO Scientific Collaboration |title=Instrument Science White Paper |url=https://dcc.ligo.org/public/0113/T1400316/004/T1400316-v5.pdf |id=LIGO-T1400316-v4 |publisher=LIGO |date=2015-02-10 |access-date=2020-06-23}}</ref>

===Cosmic Explorer===
A design for a larger facility with longer arms is called "[[Cosmic Explorer (gravitational wave observatory)|Cosmic Explorer]]".  This is based on the LIGO Voyager technology, has a similar LIGO-type L-shape geometry but with 40&nbsp;km arms. The facility is currently planned to be on the surface. It has a higher sensitivity than [[Einstein Telescope]] for frequencies beyond 10&nbsp;Hz, but lower sensitivity under 10&nbsp;Hz.<ref name=ISWP15/>