Re: how does light pass through so dense a medium as glass or dimond?

Greetings:

Reference: F. A. Jenkins, H. E. White, Fundamentals of Optics
McGraw-Hill, NY, 1950

Your question is a good one for the answer is at the heart of modern
physics and engineering. No material is transparent or opaque throughout
the electromagnetic spectrum. Our eyes can only sense a small portion of
the electromagnetic spectrum. Light is a form of electromagnetic radiation.
Other forms of electromagnetic radiation include radio waves, microwaves,
infrared radiation, ultraviolet rays, X-rays, and gamma rays. All of these,
known collectively as the electromagnetic spectrum, are fundamentally
similar in that they move at 186,000 miles per second, the speed of light
through a vacuum. The only difference between them is their wavelength,
which is directly related to the amount of energy the waves carry (photon
energy). The shorter the wavelength of the radiation, the higher the energy.

The rainbow of colors we know as visible light is the portion of the
electromagnetic spectrum with wavelengths between 400 and 700 billionths
of a meter (400 to 700 nanometers). It is the part of the electromagnetic
spectrum that we see, and we are fortunate that this coincides with the
wavelength of greatest intensity of sunlight and lowest atmospheric absorption.
Visible waves have great utility for the remote
sensing of objects and for the identification of different
objects by their visible colors. If our eyes used longer infrared wavelengths,
we would live in a dense fog all of the time because of the absorption of infrared light
by water vapor molecules in the air. As for your example, a diamond is
transparent at visible wavelengths and it is opaque in the infrared part
of the spectrum. Tissue paper can absorb or scatter light at visible wavelengths
and it is transparent to microwaves and radio waves.

When photons of electromagnetic radiation pass through a substance the
energy can be transmitted, it can be scattered or the energy can be
absorbed as heat. As the photons encounter atoms, or molecules
composed of bonded atoms, they temporarily raise the electrons of
these particles to a higher energy state (quantum level). Depending on
the physical properties of these atoms or molecules, and their physical
spacing, the electrons can reradiate an identical energy photon (the
same wavelength) in the same direction as the incident photon was
traveling. However, in this process there is a slight delay in the
transmission by each atom or molecule. This delay appears to slow down
the speed of light passing through the material and we call this the
index of refraction of the material.

The atoms or molecules could reradiate the delayed
energy in directions other than the direction of travel of the original
photons. We call this scattering. In very special materials the
reradiated photons can be changed in wavelength (color) and we call
this a nonlinear material.

Finally the atoms or molecules can
absorb the energy of the photon and convert it to heat. We call this
absorption. In most materials transmission, scattering and absorption
all occur at the same time only, dependent on the wavelength, with
different relative amounts of energy in each.
Not only do transparent materials have an index of refraction, this
index can change with wavelength (photon energy). In the visible part
of the spectrum we call this chromatic aberration which we observe in
camera and telescope lenses and prisms. However, in the general case
we call this delay dispersion. Material dispersion can change over
very great values at some places in the electromagnetic spectrum.
A resonant absorption and possible reradiation can also occur at a
very specific wavelengths and each element in the periodic table of
elements has a particular set of resonant absorption wavelengths
throughout the electromagnetic spectrum. We can use these dark
bands in the spectrum to identify the specific elements and molecules
over astronomical distances. We can also use resonant reradiation to
create lasers and atomic clocks. However, in general absorption can
occur of large portions of the spectrum.

Best regards, Your Mad Scientist
Adrian Popa