Science > Physics > Question on Snell's law for refractive index less than 1.
| Topic: |
Science > Physics |
| User: |
"Robert Clark" |
| Date: |
05 Mar 2007 04:01:31 PM |
| Object: |
Question on Snell's law for refractive index less than 1. |
As shown on this page:
Index of Refraction.
http://hyperphysics.phy-astr.gsu.edu/hbase/geoopt/refr.html#c2
the index of refraction of a medium is usually greater than 1 and will
result in the refracted light ray being bent closer to the normal in
going from the vacuum to the medium for example.
However, there are many cases were the index of refraction can be
less than 1, such as for light traveling through a plasma for example.
I'm particularly interested in ultraviolet, visible, and infrared
wavelengths.
If the refractive index for a particular wavelength is less than 1
will the light rays be bent away from the normal in going from the
vacuum to the medium?
Bob Clark
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| User: "Androcles" |
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| Title: Re: Question on Snell's law for refractive index less than 1. |
05 Mar 2007 04:52:31 PM |
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"Robert Clark" <rgregoryclark@yahoo.com> wrote in message =
news:1173132091.354342.223470@c51g2000cwc.googlegroups.com...
As shown on this page:
=20
Index of Refraction.
http://hyperphysics.phy-astr.gsu.edu/hbase/geoopt/refr.html#c2
=20
the index of refraction of a medium is usually greater than 1 and will
result in the refracted light ray being bent closer to the normal in
going from the vacuum to the medium for example.
However, there are many cases were the index of refraction can be
less than 1, such as for light traveling through a plasma for example.
I'm particularly interested in ultraviolet, visible, and infrared
wavelengths.
Ok...=20
The "index of refraction" is a number that relates one medium
to another. It does not apply to any single medium, although usually
the second medium is air. Vacuum is not a medium.=20
The index of refraction of air relative to a vacuum is very close to 1.
It will not apply to clear plastic in water, for example.
If the index of refraction of water (relative to air) is 1.333
and the index of refraction of clear plastic (relative to air)=20
is also 1.333, then the index of refraction of clear plastic in water is =
1.
In other words, light passing from water to clear plastic to water=20
will not be bent, you will not see the clear plastic when immersed
in a fish tank.
If the refractive index for a particular wavelength is less than 1
will the light rays be bent away from the normal in going from the
vacuum to the medium?
Quite obviously a prism produces colour from white light. =20
Therefore it is evident that "refractive index" is a rather loose
term that only applies at one frequency. It has a different value
for every frequency. Snell's law is not an approximation, but
white light is.
What you are asking about is "Does the refractive index ever
become less than 1?" Yes, it does, because the refractive index=20
between water and air is the reciprocal of the refractive index=20
between air and water. All you need do is have the light ray
go the other way.=20
http://www.olympusmicro.com/primer/images/refraction/criticalangle.jpg
http://www.olympusmicro.com/primer/lightandcolor/refraction.html
It will never be less than 1 going from vacuum to a medium, it will=20
be less than 1 going from a medium to a vacuum.
An index of 1 simply means straight through.
Some media have 2 indices:
=
http://www.optonlaser.com/pages_communes/glossaire/Images/Birefringence.g=
if
http://en.wikipedia.org/wiki/Birefringence
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| User: "" |
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| Title: Re: Question on Snell's law for refractive index less than 1. |
05 Mar 2007 09:52:03 PM |
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In article <1173132091.354342.223470@c51g2000cwc.googlegroups.com>, "Robert Clark" <rgregoryclark@yahoo.com> writes:
As shown on this page:
Index of Refraction.
http://hyperphysics.phy-astr.gsu.edu/hbase/geoopt/refr.html#c2
the index of refraction of a medium is usually greater than 1
True for the visible range, not all ranges.
and will
result in the refracted light ray being bent closer to the normal in
going from the vacuum to the medium for example.
However, there are many cases were the index of refraction can be
less than 1, such as for light traveling through a plasma for example.
I'm particularly interested in ultraviolet, visible, and infrared
wavelengths.
If the refractive index for a particular wavelength is less than 1
will the light rays be bent away from the normal in going from the
vacuum to the medium?
Sure.
Mati Meron | "When you argue with a fool,
meron@cars.uchicago.edu | chances are he is doing just the same"
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| User: "Robert Clark" |
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| Title: Re: Question on Snell's law for refractive index less than 1. |
06 Mar 2007 07:27:09 AM |
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On Mar 5, 10:52 pm, wrote:
In article <1173132091.354342.223...@c51g2000cwc.googlegroups.com>, "Robert Clark" <rgregorycl...@yahoo.com> writes:
As shown on this page:
Index of Refraction.
http://hyperphysics.phy-astr.gsu.edu/hbase/geoopt/refr.html#c2
the index of refraction of a medium is usually greater than 1
True for the visible range, not all ranges.
and will
result in the refracted light ray being bent closer to the normal in
going from the vacuum to the medium for example.
However, there are many cases were the index of refraction can be
less than 1, such as for light traveling through a plasma for example.
I'm particularly interested in ultraviolet, visible, and infrared
wavelengths.
If the refractive index for a particular wavelength is less than 1
will the light rays be bent away from the normal in going from the
vacuum to the medium?
Sure.
Mati Meron | "When you argue with a fool,
m...@cars.uchicago.edu | chances are he is doing just the same"
Thanks. I need a medium for which this will work in the uv, visible,
or IR range in going from the vacuum to the medium, either a solid, a
gas, or a liquid. It would be nice if it also worked over a wide
wavelength range, not just at a single wavelength.
Bob Clark
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| User: "" |
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| Title: Re: Question on Snell's law for refractive index less than 1. |
06 Mar 2007 10:59:32 AM |
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In article <1173187628.997351.192450@c51g2000cwc.googlegroups.com>, "Robert Clark" <rgregoryclark@yahoo.com> writes:
On Mar 5, 10:52 pm, wrote:
In article <1173132091.354342.223...@c51g2000cwc.googlegroups.com>, "Robert Clark" <rgregorycl...@yahoo.com> writes:
As shown on this page:
Index of Refraction.
http://hyperphysics.phy-astr.gsu.edu/hbase/geoopt/refr.html#c2
the index of refraction of a medium is usually greater than 1
True for the visible range, not all ranges.
and will
result in the refracted light ray being bent closer to the normal in
going from the vacuum to the medium for example.
However, there are many cases were the index of refraction can be
less than 1, such as for light traveling through a plasma for example.
I'm particularly interested in ultraviolet, visible, and infrared
wavelengths.
If the refractive index for a particular wavelength is less than 1
will the light rays be bent away from the normal in going from the
vacuum to the medium?
Sure.
Mati Meron | "When you argue with a fool,
m...@cars.uchicago.edu | chances are he is doing just the same"
Thanks. I need a medium for which this will work in the uv, visible,
or IR range in going from the vacuum to the medium, either a solid, a
gas, or a liquid. It would be nice if it also worked over a wide
wavelength range, not just at a single wavelength.
You ask for a lot. It does work in the x-ray regime, wavelengths
roughly from 1 nm to 0. Viewed in terms of requency this is a huge
range, from ~10^(17) to infinity. For longer wavelengths, in general
no. You can get such effect in various contrived situations, over a
limited frequency range, but I'm not aware of more than this.
Note that while in the x-ray regime the index of refraction is <1, it
is not much less, typically the difference (from 1) is in the
10^(-4) -10^(-6) range. That's enough, though, to have valuable
applications.
Mati Meron | "When you argue with a fool,
meron@cars.uchicago.edu | chances are he is doing just the same"
.
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| User: "Tom Roberts" |
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| Title: Re: Question on Snell's law for refractive index less than 1. |
07 Mar 2007 09:00:17 AM |
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wrote:
Note that while in the x-ray regime the index of refraction is <1, it
is not much less, typically the difference (from 1) is in the
10^(-4) -10^(-6) range. That's enough, though, to have valuable
applications.
I believe there are also manufactured meta-materials that exhibit this
in the microwave region (wavelength ~1 cm). They etch conductive lines
on circuit boards and layer them together to form a solid....
Tom Roberts
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| User: "" |
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| Title: Re: Question on Snell's law for refractive index less than 1. |
07 Mar 2007 10:59:18 AM |
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In article <5sAHh.123$Qw.64@newssvr29.news.prodigy.net>, Tom Roberts <tjroberts137@sbcglobal.net> writes:
mmeron@cars3.uchicago.edu wrote:
Note that while in the x-ray regime the index of refraction is <1, it
is not much less, typically the difference (from 1) is in the
10^(-4) -10^(-6) range. That's enough, though, to have valuable
applications.
I believe there are also manufactured meta-materials that exhibit this
in the microwave region (wavelength ~1 cm). They etch conductive lines
on circuit boards and layer them together to form a solid....
Yes, I remember reading about it. Mind you, the larger the
wavelength, the easier it is to manufacture structure exhibiting all
sorts of interesting behaviors, with respect to index of refraction.
Mati Meron | "When you argue with a fool,
meron@cars.uchicago.edu | chances are he is doing just the same"
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| User: "George Dishman" |
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| Title: Re: Question on Snell's law for refractive index less than 1. |
07 Mar 2007 12:00:07 PM |
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<mmeron@cars3.uchicago.edu> wrote in message
news:GbCHh.17$25.147@news.uchicago.edu...
In article <5sAHh.123$Qw.64@newssvr29.news.prodigy.net>, Tom Roberts
<tjroberts137@sbcglobal.net> writes:
mmeron@cars3.uchicago.edu wrote:
Note that while in the x-ray regime the index of refraction is <1, it
is not much less, typically the difference (from 1) is in the
10^(-4) -10^(-6) range. That's enough, though, to have valuable
applications.
I believe there are also manufactured meta-materials that exhibit this
in the microwave region (wavelength ~1 cm). They etch conductive lines
on circuit boards and layer them together to form a solid....
Yes, I remember reading about it. Mind you, the larger the
wavelength, the easier it is to manufacture structure exhibiting all
sorts of interesting behaviors, with respect to index of refraction.
You may be remembering articles from a couple of years ago when
the subject made the headlines but that was for materials with
refractive index < 0.
Initially it was in the microwave region but they seem to have
moved on to the optical as well now:
http://www.newscientisttech.com/article/dn10816.html
I believe it is these negative refractive index materials that
are interesting from the 'superlens' aspect.
George
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| User: "Robert Clark" |
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| Title: Re: Question on Snell's law for refractive index less than 1. |
20 Mar 2007 11:11:29 AM |
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On Mar 6, 12:59 pm, wrote:
In article <1173187628.997351.192...@c51g2000cwc.googlegroups.com>, "Robert Clark" <rgregorycl...@yahoo.com> writes:
...
Thanks. I need a medium for which this will work in the uv, visible,
or IR range in going from the vacuum to the medium, either a solid, a
gas, or a liquid. It would be nice if it also worked over a wide
wavelength range, not just at a single wavelength.
You ask for a lot. It does work in the x-ray regime, wavelengths
roughly from 1 nm to 0. Viewed in terms of requency this is a huge
range, from ~10^(17) to infinity. For longer wavelengths, in general
no. You can get such effect in various contrived situations, over a
limited frequency range, but I'm not aware of more than this.
Note that while in the x-ray regime theindexofrefractionis <1, it
is not much less, typically the difference (from 1) is in the
10^(-4) -10^(-6) range. That's enough, though, to have valuable
applications.
Mati Meron | "When you argue with a fool,
m...@cars.uchicago.edu | chances are he is doing just the same"
I might be able to get by with the index of refraction with the
respect to the vacuum being less than 1 for just a small wavelength
range. I could for example use filters so that only a light of typical
light bands get through and use the appropriate metamaterial lens for
each band, red, green, blue for example.
This report suggests this might be possible:
Red light debut for exotic 'metamaterial'
13:38 18 December 2006
NewScientist.com news service
Jeff Hecht
"Bending backwards
Dolling determined the refractive index of the material by measuring
the "phase velocity" of light as it passed
through. His measurements show the structure has a negative refractive
index of -0.6 for light with a wavelength of 780 nm.
This value drops to zero at 760 nm and 800 nm, and becomes positive at
longer and shorter wavelengths. Previously, the shortest wavelength at
which a negative refractive index had been demonstrated was 1400 nm."
http://www.newscientisttech.com/article/dn10816.html
Bob Clark
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| User: "" |
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| Title: Re: Question on Snell's law for refractive index less than 1. |
20 Mar 2007 11:29:02 AM |
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In article <1174407089.475902.168620@b75g2000hsg.googlegroups.com>, "Robert Clark" <rgregoryclark@yahoo.com> writes:
On Mar 6, 12:59 pm, wrote:
In article <1173187628.997351.192...@c51g2000cwc.googlegroups.com>, "Robert Clark" <rgregorycl...@yahoo.com> writes:
...
Thanks. I need a medium for which this will work in the uv, visible,
or IR range in going from the vacuum to the medium, either a solid, a
gas, or a liquid. It would be nice if it also worked over a wide
wavelength range, not just at a single wavelength.
You ask for a lot. It does work in the x-ray regime, wavelengths
roughly from 1 nm to 0. Viewed in terms of requency this is a huge
range, from ~10^(17) to infinity. For longer wavelengths, in general
no. You can get such effect in various contrived situations, over a
limited frequency range, but I'm not aware of more than this.
Note that while in the x-ray regime theindexofrefractionis <1, it
is not much less, typically the difference (from 1) is in the
10^(-4) -10^(-6) range. That's enough, though, to have valuable
applications.
Mati Meron | "When you argue with a fool,
m...@cars.uchicago.edu | chances are he is doing just the same"
I might be able to get by with the index of refraction with the
respect to the vacuum being less than 1 for just a small wavelength
range.
For a small wavelength range I'm sure you can get it. Whether it'll
be worth the effort, depends.
I could for example use filters so that only a light of typical
light bands get through and use the appropriate metamaterial lens for
each band, red, green, blue for example.
This report suggests this might be possible:
Red light debut for exotic 'metamaterial'
13:38 18 December 2006
NewScientist.com news service
Jeff Hecht
"Bending backwards
Dolling determined the refractive index of the material by measuring
the "phase velocity" of light as it passed
through. His measurements show the structure has a negative refractive
index of -0.6 for light with a wavelength of 780 nm.
This value drops to zero at 760 nm and 800 nm, and becomes positive at
longer and shorter wavelengths. Previously, the shortest wavelength at
which a negative refractive index had been demonstrated was 1400 nm."
http://www.newscientisttech.com/article/dn10816.html
Bob Clark
Mati Meron | "When you argue with a fool,
meron@cars.uchicago.edu | chances are he is doing just the same"
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| User: "Sam Wormley" |
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| Title: Re: Question on Snell's law for refractive index less than 1. |
05 Mar 2007 04:20:43 PM |
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Robert Clark wrote:
As shown on this page:
Index of Refraction.
http://hyperphysics.phy-astr.gsu.edu/hbase/geoopt/refr.html#c2
the index of refraction of a medium is usually greater than 1 and will
result in the refracted light ray being bent closer to the normal in
going from the vacuum to the medium for example.
However, there are many cases were the index of refraction can be
less than 1, such as for light traveling through a plasma for example.
I'm particularly interested in ultraviolet, visible, and infrared
wavelengths.
If the refractive index for a particular wavelength is less than 1
will the light rays be bent away from the normal in going from the
vacuum to the medium?
Bob Clark
Run the light in the opposite direction.
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| User: "" |
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| Title: Re: Question on Snell's law for refractive index less than 1. |
05 Mar 2007 05:37:48 PM |
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Yes, the refractive index of a material can now be less that 1. Such
materials have recently been created (sometimes called meta-
materials). Passing from "vacuum" to the material, the light-ray
bends aways instead of bending closer to the normal. The effect is due
to the crystalline structure and inner em-fields of the material. The
light-ray is still slower than Co but just bends the other way. But
"refractive index" has a slightly different definition in such cases.
I saw examples & details in an engineering mag a few months back. Just
google the subject.
Index of Refraction.http://hyperphysics.phy-astr.gsu.edu/hbase/geoopt/refr.html#c2
the index of refraction of a medium is usually greater than 1 and will
result in the refracted light ray being bent closer to the normal in
going from the vacuum to the medium for example.
However, there are many cases were the index of refraction can be
less than 1, such as for light traveling through a plasma for example.
I'm particularly interested in ultraviolet, visible, and infrared
wavelengths.
If the refractive index for a particular wavelength is less than 1
will the light rays be bent away from the normal in going from the
vacuum to the medium?
Bob Clark
.
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| User: "Robert Clark" |
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| Title: Re: Question on Snell's law for refractive index less than 1. |
06 Mar 2007 09:34:55 AM |
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On Mar 5, 6:37 pm, "rot...@gmail.com" <rot...@gmail.com> wrote:
Yes, the refractive index of a material can now be less that 1. Such
materials have recently been created (sometimes called meta-
materials). Passing from "vacuum" to the material, the light-ray
bends aways instead of bending closer to the normal. The effect is due
to the crystalline structure and inner em-fields of the material. The
light-ray is still slower than Co but just bends the other way. But
"refractive index" has a slightly different definition in such cases.
I saw examples & details in an engineering mag a few months back. Just
google the subject.
Yes, here's an article that discusses it:
Red light debut for exotic 'metamaterial'
13:38 18 December 2006
NewScientist.com news service
Jeff Hecht
"Bending backwardsDolling determined the refractive index of the
material by measuring the "phase velocity" of light as it passed
through. His measurements show the structure has a negative refractive
index of -0.6 for light with a wavelength of 780 nm.
This value drops to zero at 760 nm and 800 nm, and becomes positive at
longer and shorter wavelengths. Previously, the shortest wavelength at
which a negative refractive index had been demonstrated was 1400 nm."
http://www.newscientisttech.com/article/dn10816.html
For my application I actually need the refractive index to be
positive, but less than 1. The case where it is negative swings the
refracted light ray to the other side of the normal.
I'm puzzled by the zero refractive index at some wavelengths however.
This should mean the phase velocity should be infinite, but what would
a wave traveling at infinite velocity be?
Bob Clark
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