Transcript Free Electron Laser

Free Electron Laser
FEL
• A free-electron laser, or FEL, is a laser that shares the same
optical properties as conventional lasers such as emitting a
beam consisting of coherent electromagnetic radiation
which can reach high power, but which uses some very
different operating principles to form the beam. Unlike gas,
liquid, or solid-state lasers such as diode lasers, in which
electrons are excited in bound atomic or molecular states,
FELs use a relativistic electron beam as the lasing medium
which moves freely through a magnetic structure, hence
the term free electron. The free-electron laser has the
widest frequency range of any laser type, and can be widely
tunable, currently ranging in wavelength from microwaves,
through terahertz radiation and infrared, to the visible
spectrum, to ultraviolet, to X-rays.
Beam creation
Beam creation
• To create an FEL, a beam of electrons is accelerated to almost light speed
(technically known as relativistic speed). The beam passes through an FEL
oscillator in the form of a periodic, transverse magnetic field, produced by
arranging magnets with alternating poles within a laser cavity along the
beam path. This array of magnets is sometimes called an undulator, or a
"wiggler", because it forces the electrons in the beam to assume a
sinusoidal path. The acceleration of the electrons along this path results in
the release of a photon (synchrotron radiation). Since the electron motion
is in phase with the field of the light already emitted, the fields add
together coherently. Whereas conventional undulators would cause the
electrons to radiate independently, instabilities in the electron beam
resulting from the interactions of the oscillations of electrons in the
undulators and the radiation they emit leads to a bunching of the
electrons, which continue to radiate in phase with each other.[4] The
wavelength of the light emitted can be readily tuned by adjusting the
energy of the electron beam or the magnetic field strength of the
undulators.
Holografija
• Holography was discovered in 1947 by Hungarian physicist Dennis
Gabor (Hungarian name: Gábor Dénes) (1900–1979), work for
which he received the Nobel Prize in Physics in 1971. It was made
possible by pioneering work in the field of physics by other
scientists like Mieczysław Wolfke who resolved technical issues that
previously made advancements impossible. The discovery was an
unexpected result of research into improving electron microscopes
at the British Thomson-Houston Company in Rugby, England, and
the company filed a patent in December 1947 (patent GB685286).
The technique as originally invented is still used in electron
microscopy, where it is known as electron holography, but
holography as a light-optical technique did not really advance until
the development of the laser in 1960.
Snimanje slike
Rekonstrukcija
slike
General properties of recording
materials for holography
Material
Reusable
Processing
Type of
hologram
Max.
efficiency
Amplitude
6%
Required
exposure
[mJ/cm²]
Resolution
limit [mm−1]
0.001–0.1
1,000–10,000
Photographic
No
emulsions
Wet
Phase
(bleached)
60%
Dichromated
No
gelatin
Wet
Phase
100%
10
10,000
Photoresists
No
Wet
Phase
33%
10
3,000
Yes
Charge and
heat
Phase
33%
0.01
500–1,200
No
Post exposure Phase
100%
1–1,000
2,000–5,000
Yes
None
Amplitude
2%
10–100
>5,000
Yes
None
Phase
100%
0.1–50,000
2,000–10,000
Photothermo
plastics
Photopolyme
rs
Photochromic
s
Photorefracti
ves
Confocal microscopy
• Confocal microscopy is an optical imaging
technique used to increase micrograph
contrast and/or to reconstruct threedimensional images by using a spatial pinhole
to eliminate out-of-focus light in specimens
that are thicker than the focal plane. This
technique has gained popularity in the
scientific and industrial communities and
typical applications are in life sciences and
semiconductor inspection.
What is fluorescence
If you shine light on some molecules, you may see light of a
different color emitted from those molecules. This is known as
fluorescence. The molecules absorb high-energy light (blue, for
example). This increases the energy of the molecules, represented
as the top black line in the diagram (an "excited" molecule). Some
of the energy from the blue photon is lost internally (represented
by the red squiggly arrow in the picture). The molecule then emits a
photon with less energy, green in this example. Fluorescein is a
common dye that acts in exactly this way, emitting green light when
hit with blue excitation light. The color of light emitted is material
dependent, and likewise the excitation light wavelength depends on
the material. (There are other forms of inelastic scattering;
fluorescence is particularly strong.)
Shema
http://www.physics.emory.edu/~week
s/confocal/