Silicon, gallium arsenide and other popular semiconductors have optical refractive index of above 3, but they are not transparent in visible range. Is there anything with similarly high refract index, but still highly transparent at least at the edge of visible spectrum, i.e. for the wavelength of 750 nm?
In the visible region of the spectrum, I think that the highest refractive index (of a normal material) is that of diamond (≈2.5). Cubic Zirconia (looks a bit like diamond but cheaper!) is also above 2
I think TiO2 has the highest refractive index among transparent dielectrics in visible range.
http://refractiveindex.info is worth checking out. Not comprehensive, but with some very useful data.
http://refractiveindex.info/?shelf=main&book=Si3N4&page=Philipp
http://refractiveindex.info/?shelf=main&book=TiO2&page=Devore-o
http://refractiveindex.info/?shelf=main&book=ZrO2&page=Wood
http://refractiveindex.info/?shelf=main&book=C&page=Peter
Al_xGa_1-xAs also has a high refractive index. even for x=1 the refractive index is approx. 3 at 800 nm
http://www.batop.de/information/n_AlGaAs.html
and the bandgap is in the visible at ~2.2 eV (corresponding to ~564 nm)
http://www.ioffe.ru/SVA/NSM/Semicond/AlGaAs/bandstr.html
Best regards,
Arne
Some II-VI based semiconductors such as ZnTe which transparent in the visible, ZnxCd(1-x)Te in almost all proportions
Thank you all, I've just found that certain amorphous silicon compositions can also be transparent at the edge of visible range, with refractive index almost reaching 4.
Alexander, could you please send me the references regarding that certain amorphous silicon? Thanks!
Thanks, Rathinam. Could you please send the refractive index dispersion for those?
The material with a high refractive index and has high permeability in the NIR region is (Bare Borosilicate Crown Glass, BK-7).
Ammar Qasem - is there is reason you recommend BK7 over other optical glasses?
BK7 and similar borosilicate crown glasses have rather low refractive index compared with other optical glasses. Its index is slightly lower than common soda lime glass, commonly used for windows and beverage bottles.
At 587.6 nm some refractive indices, nd are:
- Soda lime glass: 1.5234
- Borosilicate crown, e.g. Schott BK7 1.5168
- Dense flint glass, e.g. Schott SF66: 1.9229
And some transparent crystalline materials:
- Silicon nitride: 2.0458
- Zirconina: 2.1588
- Diamond: 2.4168
- Titanium dioxide: 2.6142
https://en.wikipedia.org/wiki/File:Abbe-diagram_2.svg
https://refractiveindex.info/?shelf=glass&book=BK7&page=SCHOTT
https://refractiveindex.info/?shelf=glass&book=SCHOTT-SF&page=SF66
https://www.oharacorp.com/pdf/datasheets/S-TIH57-2020-06.pdf
https://refractiveindex.info/?shelf=glass&book=soda-lime&page=Rubin-clear
Alan Robinson - This type of glass is recommended due to its very high transmittance in the spectral region from 400 nm to 2500 nm. Its refractive index can be controlled by forming multiple layers that reduce the transmittance and increase the reflectivity and thus increase the refractive index. It is possible to create multiple layers of this glass by depositing two metals of two different working functions, such as aluminum, for example, from the top and depositing a layer of silver on the bottom side, which will obtain a multi-layer reflection system that can be used in spacecraft to save the temperature of the spacecraft and control the rays that fall on its exterior surface and work on its reflection away from the surface.
Ammar Qasem - BK7 and similar borosilicate crown glasses are widely used for visible and near infra-red components, but the refractive index is relatively low compared with other optical glasses.
If transmission over a broad spectral range is paramount, a fused synthetic silica such as Infrasil supports a wider transmission window from 300 nm to 3000 nm. If UV trasmission is important, a UV grade silica manufactured by flame hydrolysis may be more appropriate
https://www.thorlabs.com/newgrouppage9.cfm?objectgroup_id=714
https://www.thorlabs.com/newgrouppage9.cfm?objectgroup_id=3983
Can you explain how a reduction in transmission leads to an increase in refractive index? Are you suggesting some kind of resonant structure which increases the group delay, or is this a means to increase the bulk refractive index in an optically homogeneous material?
Metals typically show high reflectivity for visible wavelengths due to the presence of unbound conductance band electrons. This results in very strong absorption, and a reduction in refractive index at frequencies well above the plasma resonance. The refractive index of silver is typically less than 0.1 at visible wavelengths.
https://web.mit.edu/8.13/8.13c/references-fall/aip/aip-handbook-section6g.pdf
Absorption coefficients for silver and aluminium are of order 106 cm-1 at 750 nm. Most incident light is reflected, and any ray propagating into the metal is strongly absorbed within a few nanometres.
https://refractiveindex.info/?shelf=main&book=Ag&page=McPeak
https://refractiveindex.info/?shelf=main&book=Al&page=McPeak
Very thin metallic films can be used to manufacture Fabry-Perot cavities and similar narrow band filters. However dielectric stack reflectors will generally provide higher Q and much lower insertion losses than metallic films.
Regarding multi-layer insulation for thermal control on spacecraft, I am surprised to hear that borosilicate glass is used as a substrate. Multiple layers of Kapton or Mylar film are more commonly employed, and will be flexible, lighter in weight and far more robust than a coated glass film.
https://en.wikipedia.org/wiki/Multi-layer_insulation
I am thinking to develop particular type of photonic integrated devices and I am going to submit my PhD thesis on photonic devices at the end of current semester (probably May-June 2021). what are the best options that, I have after my thesis submission?
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