View source for Engineering:Solar-blind technology

{{Short description|Imaging technology}}
'''Solar-blind technology''' is a set of technologies to produce images without interference from the Sun. This is done by using wavelengths of [[Physics:Ultraviolet|ultraviolet]] light that are totally absorbed by the [[Physics:Ozone layer|ozone layer]], yet are transmitted in the Earth's atmosphere. Wavelengths from 240 to 280&nbsp;nm are completely absorbed by the ozone layer. Elements of this technology are ultraviolet light sources, ultraviolet image detectors, and filters that only transmit the range of wavelengths that are blocked by ozone.<ref>{{cite journal |last1=Paiva |first1=Edinei C. |last2=Oliveira |first2=Fernanda P. |last3=Ghosh |first3=Santunu |last4=Pacheco |first4=Tiago S. |last5=Leite |first5=Ramon R. |last6=de Souza |first6=Rafael L. |last7=Ludwig |first7=Zélia M.C. |last8=Martins |first8=Maximiliano D. |title=Synthesis and Vibrational Spectroscopy of ( N H 4 ) 2 C o C r x S 1 - x O 4 2 . 6 H 2 O Tutton's Salt |journal=Vibrational Spectroscopy |date=October 2020 |pages=103178 |doi=10.1016/j.vibspec.2020.103178}}</ref> A system will also have a signal processing system, and a way to display the results (image).<ref name=wang/>

==Ultraviolet sources==
Ultraviolet illumination can be produced from longer wavelengths using non-linear optical materials. These can be a second harmonic generator. They must have a suitable birefringence in order to phase match the output frequency doubled UV light. One compound commercially used is L-arginine phosphate monohydrate known as LAP.<ref>{{cite journal |last1=Lu |first1=Jing |last2=Liu |first2=Xin |last3=Zhao |first3=Min |last4=Deng |first4=Xue-Bin |last5=Shi |first5=Ke-Xin |last6=Wu |first6=Qian-Ru |last7=Chen |first7=Ling |last8=Wu |first8=Li-Ming |title=Discovery of NLO Semiorganic (C 5 H 6 ON) + (H 2 PO 4 ) − : Dipole Moment Modulation and Superior Synergy in Solar-Blind UV Region |journal=Journal of the American Chemical Society |date=1 March 2021 |pages=jacs.1c00959 |doi=10.1021/jacs.1c00959|pmid=33646792 }}</ref> Research is underway for substances that are very non-linear, have a suitable [[Physics:Birefringence|birefringence]], are transparent in the spectrum and have a high degree of resistance to damage from lasers.<ref>{{cite journal |last1=Lu |first1=Jing |last2=Liu |first2=Xin |last3=Zhao |first3=Min |last4=Deng |first4=Xue-Bin |last5=Shi |first5=Ke-Xin |last6=Wu |first6=Qian-Ru |last7=Chen |first7=Ling |last8=Wu |first8=Li-Ming |title=Discovery of NLO Semiorganic (C 5 H 6 ON) + (H 2 PO 4 ) − : Dipole Moment Modulation and Superior Synergy in Solar-Blind UV Region |journal=Journal of the American Chemical Society |date=10 March 2021 |volume=143 |issue=9 |pages=3647–3654 |doi=10.1021/jacs.1c00959}}</ref>

==Optical system==
Normal glass does not transmit below 350&nbsp;nm, so it is not used for optics in solar-blind systems. Instead [[Chemistry:Calcium fluoride|calcium fluoride]], fused silica, and [[Chemistry:Magnesium fluoride|magnesium fluoride]] are used as they are transparent to shorter wavelengths.<ref name=wang/>

==Filters==
An optical filter can be used to block out visible light and near-ultraviolet light. It is important to have a high transmittance within the solar-blind spectrum, but to strongly block the other wavelengths.<ref name=wang/>

Interference filters can pass 25% of the wanted rays, and reduce others by 1000 to 10,000 times. However they are unstable and have a narrow field of view.

Absorption filters may only pass 10% of wanted UV, but can reject by a ratio of 10<sup>12</sup>. They can have a wide field of view and are stable.

==Ultraviolet detectors==
Semiconductor ultraviolet detectors are solid state, and convert an ultraviolet photon into an electric pulse. If they are transparent to visible light, then they will not be sensitive to light.<ref name=wang/>

{|class="wikitable"
!name
!limit nm
!efficiency
!ref
|-
|hexagonal [[Chemistry:Boron nitride|boron nitride]]
|300
|
|<ref>{{cite journal |last1=Aldalbahi |first1=Ali |last2=Feng |first2=Peter |title=Development of 2-D Boron Nitride Nanosheets UV Photoconductive Detectors |journal=IEEE Transactions on Electron Devices |date=June 2015 |volume=62 |issue=6 |pages=1885–1890 |doi=10.1109/TED.2015.2423253|bibcode=2015ITED...62.1885A |s2cid=22529949 }}</ref>
|-
|hydrogenated [[Chemistry:Amorphous silicon|amorphous silicon]]
|187
|20%
|<ref name=cap>{{cite journal |last1=Caputo |first1=D. |last2=de Cesare |first2=G. |last3=Irrera |first3=F. |last4=Palma |first4=F. |title=Solar-blind UV photodetectors for large area applications |journal=IEEE Transactions on Electron Devices |date= |volume=43 |issue=9 |pages=1351–1356 |doi=10.1109/16.535318|bibcode=1996ITED...43.1351C }}</ref>
|-
|amorphous [[Chemistry:Silicon carbide|silicon carbide]]
|187
|20%
|<ref name=cap/>
|-
|[[Chemistry:Gallium nitride|gallium nitride]]
|
|
|
|-
|[[Chemistry:Zinc oxide|zinc oxide]]
|
|
|
|-
|[[Chemistry:Diamond|diamond]]
|
|
|
|-
|[[Physics:Photomultiplier tube|photomultiplier tube]]
|300
|30%
|<ref>{{Cite web|title="Eyes" that Discover Ultraviolet Light –Solar-blind Photomultiplier Tube -- Opto-Electronic Journals|url=http://www.oejournal.org/item/news2019024.html|access-date=2021-03-08|website=www.oejournal.org}}</ref>
|}

==Use==
Solar-blind imaging can be used to detect corona discharge, in electrical infrastructure. Missile exhaust can be detected from the troposphere or ground. Also when looking down on the Earth from space, the Earth appears dark in this range, so rockets can be easily detected from above once they pass the ozone layer.<ref name=wang>{{cite book |last1=Wang |first1=Baohua |last2=Wang |first2=Yuanyuan |last3=Zhong |first3=Xiaoming |last4=Ruan |first4=Ningjuan |editor1-first=Ailing |editor1-last=Tian |editor2-first=Anand |editor2-last=Asundi |editor3-first=Weiguo |editor3-last=Liu |editor4-first=Chunmin |editor4-last=Zhang |title=The International Conference on Photonics and Optical Engineering (IcPOE 2014) |chapter=Research on solar-blind UV optical imaging system |date=20 February 2015 |volume=9449 |pages=94492L |doi=10.1117/12.2083301|s2cid=135710510 }}</ref>
Israel,  People's Republic of China, Russia, South Africa, United Kingdom, and United States are developing this technology.<ref>{{cite journal |last1=Manomenova |first1=V L |last2=Rudneva |first2=E B |last3=Voloshin |first3=A E |title=Crystals of the simple and complex nickel and cobalt sulfates as optical filters for the solar-blind technology |journal=Russian Chemical Reviews |date=30 June 2016 |volume=85 |issue=6 |pages=585–609 |doi=10.1070/RCR4530|bibcode=2016RuCRv..85..585M }}</ref>

==References==
{{Reflist}}

[[Category:Ultraviolet radiation]]

{{Sourceattribution|Solar-blind technology|1}}