wave propagation Flashcards
(near field) propagation
fresnel
(far field) propagation
fraunhofer
First order approximation to propagation problem:
Geometric Optics
the phase velocity changes in matter
compared to vacuum by a factor
n: refraction index
for visible light: n1 ?? 1
for X-rays: n1 ?? 1
for visible light: n1 > 1
for X-rays: n1 < 1
n is complex and for X-rays often written as
n = 1- delta + i*beta
delta: phase shift of wave in matter
beta: attenuation
The direction of the waves is given
by the
wavevector: kn
kn = 2pi / (lambda n)
snells law
n0 * sin(theta0) = n1 * sin(theta1)
Huygens-Fresnel principle
Optical field in observation plane can be expressed as sum of spherical waves
exp(ikr)/abs(r)
Corpuscular Theory
particle theory of light
Interference of light
Double Slit Experiment done by
1804 Thomas Young
1804 Intensity of interference
1815 Polarisation done by
Augustin Jean Fresnel
Collimated work on electricity and magnetism
of Michael Faraday and André-Marie Ampère done by
1864 james clark maxwell
For isotropic media the polarization does not ………and we restrict ourself to …….. waves
For isotropic media the polarization does not change and we restrict ourself to scalar waves
à for electromagnetic waves of the velocity c
c = lambda * v
c = 1/sqrt(mu0*eps0)
Gauss’ theorem
connects the flux of the vector field
through a closed surface surrounding a volume
with the diverence of this field in the volume
divergence of a vector field
within a volume is equal to flux of the vector field
through surface with
normal vector n
the integral theorem of Helmholtz and Kirchhoff
it allows to calculate the field at point P0 by integrating over a closed surface around P0
Geometric optics ………… to describe diffraction and interference
insufficient
Scalar Theory:
only a single component of E or B
and no polarization
What are the components of the Fresnel-Kirchhoff diffraction integral
Wave Source:
Integration Variables:
two integration variables: one representing the coordinates of the points on the diffracting aperture or obstacle, and the other representing the observation point in the far-field region where the diffracted wave is being analyzed.
Amplitude Factor:
Phase Factor:
Aperture Function:
Geometrical Factor:
Paraxial ray is a ray that makes
small angle to optical axis
With paraxial & Taylor assumptions
* Free space propagation impulse response becomes
parabolic shape
When to use Fresnel propagation?
Fresnel propagation is valid if
Fresnel number F = a*a/(lambda * z) >= 1
Fresnel propagation also known as
near field