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| PhotoTechEDU Day 8: Diffraction and Interference in Imaging |
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Google Tech Talks
March 14, 2007
ABSTRACT
Photographic Technology Day 8: This session
addresses effects of the wave nature of
light. This approach will allow us to talk
about the phenomena of interference as well
as diffraction. The understanding of the
notion of diffraction will be used to
determine the Rayleigh criteria and finally
the resolving power of an optical system. In
the second part of the lecture, we will study
gratings using the wave approach. An example
of an amateur spectroscope for astronomy
using a reflective grating will be shown.
Credits: Speaker:Rom Clement
Tags : google howto phototechedu day diffraction |
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Affichage : 2997
Durée : 3286 s |
| Electron Diffraction to Tchaikovsky Waltz of the Flowers |
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Did this about 10 years ago for my physics
degree final year project - numerical
solutions to the time-dependent Schrödinger
Equation (TDSE) applied to electron
diffraction. Primarily we were interested in
the effects of different slit geometries, as
this had never been studied before (for
example there's no way you could analytically
solve Kirchoff's diffraction theory to
anything other than 1-D slits, that is, slits
without thickness and funny shapes) - all is
performed in dimensionless units.
The electron is modelled here as a
wavepacket, that is, a Gaussian distribution
superimposed with a sinusoidal wave term, and
it interacts in the TDSE with the potential
boundary of a double-slit wall, I also
investigated other potentials and confines,
including an elliptical potential, which was
an idea based on what was then a recent
publication by IBM laboratories on their STM
atom manipulation on substrates - in
particular the Stadium Corral. I wanted to
approximate the effect they observed with
wave effects on the surface state electron
density, with the peaks at the foci of the
ellipse. They observed that an impurity at
one focus led to the disappearance of the
peak at the other focus, due to the wave
nature to the electron distribution. I never
quite got that far as it would have required
a lot more computing power (and it was way
beyond the objective of the project), but
focusing of the electron packet can be
observed.
The most advanced desktop PCs I had at my
disposal were PII 300 MHz machines - I
commandeered 4 machines in our IT room (which
got me in trouble with IT dept for never
logging out - I disabled their auto
logout/reboot scripts which ran a disk
cleaner, deleting all user files after
midnight - they even blocked my account for a
couple of days!) - these machines spent the
next month solving the TDSE for a number of
conditions via the predictor-corrector
method, approximating the differential
equations with finite steps, in good old
Fortran. This method, however, results in two
opposing initial directions for the wave
packet to move in, hence the electron splits
in two.
Time-dependence therefore suggests that the
resulting data be presented in some sort of
movie (though not just a movie - time
averaged plots can and was also done besides
this, for comparison with classical
diffraction), so the final probability
distribution data was then rendered frame by
frame in Matlab. At that time Matlab was a
bit basic, you couldn't automatically grab
each frame and convert into a movie like you
can now. Consequently each frame had to be
manually saved as a bmp, all 7000 or so, then
imported into some basic animation package, I
forget what is is now. For a bit of fun I
added the marvellous Waltz of the Flowers by
Tchaikovsky. Nobody can write music like he
did!
The "finé" at the end was a play on the
French word for finished - "fini" - all the
French people I knew / met at university
seemed to say "é" at the end of everything!
Tags : electron difrraction qauntum numerial computation time depedent Schroedinger Equation Tchaikovsky Waltz of the Flowers |
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Affichage : 1086
Durée : 335 s |
| Diffraction Gratings & green laser Demo Tutorial |
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Diffractin gratings
http://www.dragonlasers.com
Demonstration tutorial of a Viper laser
pointer and 3 types of starburst diffraction
grating.
Viper is courtesy of
http://www.dragonlasers.com
starburst Diffractin grating are courtesy of
http://search.ebay.com.au/ws/search/SaleSearc
h?sofocus=bs&satitle=diffraction+grating&saca
t=-1%26catref%3DC5&fbd=1&_trksid=m37&from=R6&
nojspr=y&pfid=0&fswc=1&few=&saprclo=&saprchi=
&fss=1&saslop=1&sasl=goodly88088&fls=4%26floc
%3D1&sargn=-1%26saslc%3D0&salic=15&saatc=15&s
adis=200&fpos=2774&fsct=&sacur=0&sacqyop=ge&s
acqy=&sabfmts=0&saobfmts=exsif&ga10244=10425&
ftrt=1&ftrv=1&sabdlo=&sabdhi=&saaff=afdefault
&afcj=&afmp=&fsop=1%26fsoo%3D1&fcl=2&frpp=100
Tags : laser lasers lazer lazers portable green pointer pointers powerful high power burn balloon starburst diffraction grating |
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Affichage : 8158
Durée : 128 s |
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