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Young M. Optics and lasers.. including fibers and optical waveguides (ISBN 354065741X)(5ed., Springer, 1998)(KA)(T)(511s)_EO_.djvu |
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Size 4.1Mb Date Nov 19, 2003 |
8.5 Laser Safety 235
sign...
Radiation between the wavelengths of 1.4 and 3 fim penetrates to the lens
and may cause cataracts; longer-wavelength infrared radiation is absorbed
near the surface of the cornea and can cause damage there...
The danger from the short-wavelength radiation is potentially increased
with some sunglasses if .they are on average dark enough to increase the
Problems 237
pupil diameter and yet are manufactured so that they transmit harmful
wavelengths selectively...
What is this diameter for L = 1 m and A = 1.06 |am
(Nd:YAG)?
8.8 We need to know the spot radius w0 of a Gaussian beam at the focal point
ot a 40 x microscope objective...
Light is reflected whenever it strikes a boundary
between media that have different indexes of refraction...
The most prominent
features of the graph are the existence of the Brewster angle at 57° and
the rapid approach to 100% reflectance at grazing incidence (i — tt/2)...
If the wave is
polarized with its electric-field vector perpendicular to the plane of incidence,
the phase shift (£>± is given implicitly by the equation
where \i = n/n' > 1, and sinic = 1/fj....
Because of the phase shift, a ray appears to penetrate slightly into the
less dense medium before emerging and being reflected...
However, because of the
anisotropy of the crystal, the wavelet is not a sphere but rather an ellip-
ellipsoid of revolution when the electric-field vector oscillates in the plane of the
248 9...
The wave is plane polarized,
its electric-field vector making angle 9 with the optic axis of the crystal...
Because of the small index difference between the extraordinary ray and
the ordinary ray, the Glan-Thompson prism has a very small angular toler-
tolerance...
Electromagnetic and Polarization Effects
Polarizing films are almost uniformly gray throughout the visible and
transmit highly polarized light...
In short, X2 is not a constant, but
a tensor, and the correct expression for the second-harmonic polarization is
WM (9.15)
B)
where i,j,k represent x,y, or z...
We may, in addition, consider
the nonlinear polarization that results from the interaction of two fields with
different frequencies u)\ and lo2...
The
optic axis induced by the field is parallel to the direction of the field; for
constant electric-field strength, the liquid behaves exactly as a birefringent
crystal with indexes of refraction no (the index of the material in the absence
of the field) and ne...
Second, the index difference (no — ne)' depends on electric-
field strength in the crystal, not on the voltage between the electrodes...
Under proper con-
conditions, nearly all of the incident light may be diffracted, or deflected, into
angle 9...
The rotation induced by the magnetic field is equal
to
VBl , (9.35)
where B is the magnetic field strength, I is the length of the specimen, and
V is a constant known as the Verdet constant...
Because of this index
variation, rays that are inclined at an angle to the axis travel, on the aver-
average, through a medium that has a lower index of refraction than the index
along the axis...
That is, the compo-
component nikcosi perpendicular to the waveguide axis exhibits constructive in-
interference between the two interfaces...
If we multiply both sides of
this equation by 2vr/A and rearrange slightly, we find that
A;3sini3 = kini sin?! + It:jd! ...
This is so because diffraction by the edges of the waveguide
will spread an incident plane wave into a range of angles and allow excitation
of more than one mode...
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