Posted by
Craig Brideau on
URL: http://confocal-microscopy-list.275.s1.nabble.com/Refraction-and-Dispersion-phase-contrast-tp7579532p7579534.html
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Wavelength doesn't really exist; it's a metric we came up with to describe
specific frequencies in a numerically convenient manner, more or less. If
you could 'freeze time' and hold a ruler up to monochromatic light then in
theory you could measure the length of one oscillation of the light. In
air, this follows f = c/lambda where f = frequency, c = speed of light in
vacuum, and lambda is wavelength. In glass you have to modify the speed of
light by no/nmat where no is 1 (index of refraction of vacuum) and nmat is
index of refraction of the material the light is propagating through. If
you do the 'freeze time' trick again and try to measure the wave as it
passes through glass, you will find the wave is 'bunched up' a bit as it
propagates slower through matter than vacuum. However, if you observe at
an infinitely small point as the wave goes by, and unfreeze time, you will
record exactly the same frequency regardless of the material you are in.
It's Monday where I am so please take what I say with a grain of salt.
@:-)
Craig
On Mon, Jan 21, 2013 at 11:53 AM, MODEL, MICHAEL <
[hidden email]> wrote:
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>
> Hi Claire - the speed of light does change but the eye responds only to
> frequency, it doesn't know anything about wavelength. And the frequency
> remains the same throughout all transformations of the wave.
>
> Mike
>
> -----Original Message-----
> From: Confocal Microscopy List [mailto:
[hidden email]]
> On Behalf Of Claire Brown, Dr.
> Sent: Monday, January 21, 2013 1:30 PM
> To:
[hidden email]
> Subject: Refraction and Dispersion-phase contrast
>
> *****
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>
> I am teaching a class on light microscopy and have two questions:
>
> 1) If higher refractive indices materials slow down the speed of light
> does the wavelength also change so that frequency and energy are conserved?
> If this is true does is the wavelength shift so small that the colour does
> not change a great deal? The other explanation I had is that the speed of
> light never changes but short wavelengths take longer to travel through
> high NA materials because they interact with the material and travel along
> a longer path to reach the other side of the material. So the speed does
> not change, the wavelength does not change but the light takes longer to
> get through the material.
>
> 2) Does diffracted light shift by exactly 1/4 a wavelength in phase from
> incident light? If so why is it exactly 1/4 of a wavelength?
>
> Sorry for my basic questions but these sometimes seem harder to explain
> and understand than more complex concepts.
>
> Sincerely,
>
> Claire
>