3B Scientific Laser Optics Supplemental Set - Manual (Page 20)

20
E6a Refraction of light passing glass-air boundary
(U17300, transparency F)
The ray is refracted with the refraction angle ß, which
is larger than
α
. The ray is bent away from the normal.
E6b Refraction on glass prism edge
(U17300/U17301)
When light passes through glass to air, Snell’s law can
be written in the next form:
n
1
sin
α
= sin ß
Refractive index of air n
2
= 1.
E6c Critical angle, total reflection
(U17300, transparency F)
The larger the incidence angle the larger the refrac-
tion angle. If n
1
< n
2
a critical angle
α
exists. In other
words, the refracted ray lies on the border of two me-
diums. When the incidence angle is larger than the
critical angle, there is no more refracted light and all
light energy is reflected, this is called total reflection.
E6d Total reflection – propagating of light in
optical fibres
(U17300)
If light enters the optical fibre under some angles it
propagates in it using the total reflection on the bor-
ders of the fibre. An important parameter determines
what angle should not be overcome. This parameter is
called the numerical aperture. It is SIN of the maxi-
mum entrance angle of the light. Also the minimal
radius of the fibre bent is set by this parameter. It
cannot be smaller, when the fibre is installed.
E7 Light ray shift by glass planparallel plate
(U17300/U17301)
If a light ray passes through a planparallel plate its
direction is not changed. The outgoing ray is shifted in
accordance with the incoming one. The shift d can be
estimated with respect to the thickness h of the plate
using the formula:
d h
=
− ( )
sin
cos
α β
β
Acrylic
Acrylic
Air
Acrylic
Acrylic
Air