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1
Laser Cooling - Sixty Symbols
Laser Cooling - Sixty Symbols
::2010/08/23::
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2
Laser Cooling - From Atomic Clocks to Watching Biomolecules with Steven Chu
Laser Cooling - From Atomic Clocks to Watching Biomolecules with Steven Chu
::2008/01/10::
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3
Lesson23: Laser Cooling!
Lesson23: Laser Cooling!
::2013/03/14::
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4
How Doppler Cooling Works
How Doppler Cooling Works
::2012/07/10::
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5
Absolute Zero- Nobel Prize
Absolute Zero- Nobel Prize
::2010/02/28::
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6
Using Laser Cooling to Mark Time
Using Laser Cooling to Mark Time
::2011/05/20::
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7
Laser Cooling (extra footage)
Laser Cooling (extra footage)
::2010/08/24::
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8
David DeMille , "Laser cooling and slowing of diatomic molecule"
David DeMille , "Laser cooling and slowing of diatomic molecule"
::2012/06/19::
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9
Oxford Sparks: Towards Absolute Zero
Oxford Sparks: Towards Absolute Zero
::2012/07/18::
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10
Laser Cooling
Laser Cooling
::2012/06/17::
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11
YTP: William Phillips talks about laser cooling
YTP: William Phillips talks about laser cooling
::2012/11/05::
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12
Frontiers in Laser Cooling, Single-Molecule Biophysics and Energy Science: Wolfgang Ketterle
Frontiers in Laser Cooling, Single-Molecule Biophysics and Energy Science: Wolfgang Ketterle
::2008/10/03::
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13
Frontiers in Laser Cooling, Single-Molecule Biophysics and Energy Science: Carlos Bustamante
Frontiers in Laser Cooling, Single-Molecule Biophysics and Energy Science: Carlos Bustamante
::2008/10/03::
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14
Frontiers in Laser Cooling, Single-Molecule Biophysics and Energy Science: Eric Cornell
Frontiers in Laser Cooling, Single-Molecule Biophysics and Energy Science: Eric Cornell
::2008/10/03::
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15
Frontiers in Laser Cooling, Single-Molecule Biophysics and Energy Science: Carl Wieman
Frontiers in Laser Cooling, Single-Molecule Biophysics and Energy Science: Carl Wieman
::2008/10/03::
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16
homemade diy laser cooling systems
homemade diy laser cooling systems
::2010/04/07::
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17
Frontiers in Laser Cooling, Single-Molecule Biophysics and Energy Science: Mark Kasevich
Frontiers in Laser Cooling, Single-Molecule Biophysics and Energy Science: Mark Kasevich
::2008/10/03::
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18
Frontiers in Laser Cooling, Single-Molecule Biophysics and Energy Science: Steve Quake
Frontiers in Laser Cooling, Single-Molecule Biophysics and Energy Science: Steve Quake
::2008/10/03::
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19
Brian Odom, "Sympathetic cooling of molecules with laser-cooled atoms"
Brian Odom, "Sympathetic cooling of molecules with laser-cooled atoms"
::2013/10/17::
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20
Frontiers in Laser Cooling, Single-Molecule Biophysics and Energy Science: Paul Alivisatos
Frontiers in Laser Cooling, Single-Molecule Biophysics and Energy Science: Paul Alivisatos
::2008/10/03::
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21
Frontiers in Laser Cooling, Single-Molecule Biophysics and Energy Science: Steve Chu
Frontiers in Laser Cooling, Single-Molecule Biophysics and Energy Science: Steve Chu
::2008/10/02::
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22
Physics 111: Atom Trapping (MOT)
Physics 111: Atom Trapping (MOT)
::2012/03/08::
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23
Nike Football: Laser-Cooled Perfection
Nike Football: Laser-Cooled Perfection
::2012/04/16::
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24
Laser Cooling (Quiz)
Laser Cooling (Quiz)
::2012/08/13::
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25
Eric Hudson, "Sympathetic cooling of molecules with laser-cooled atoms"
Eric Hudson, "Sympathetic cooling of molecules with laser-cooled atoms"
::2013/10/17::
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26
Frontiers in Laser Cooling, Single-Molecule Biophysics and Energy Science: Jay Keasling
Frontiers in Laser Cooling, Single-Molecule Biophysics and Energy Science: Jay Keasling
::2008/10/03::
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27
Laser cooling flow sensor
Laser cooling flow sensor
::2009/10/11::
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28
Laser Cooling Demonstration
Laser Cooling Demonstration
::2013/04/18::
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29
Frontiers in Laser Cooling, Single-Molecule Biophysics and Energy Science: Leo Hollberg and Allen Mills
Frontiers in Laser Cooling, Single-Molecule Biophysics and Energy Science: Leo Hollberg and Allen Mills
::2008/10/03::
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30
Frontiers in Laser Cooling, Single-Molecule Biophysics and Energy Science: Vladan Vuletic and Cheng Chin
Frontiers in Laser Cooling, Single-Molecule Biophysics and Energy Science: Vladan Vuletic and Cheng Chin
::2008/10/03::
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31
Frontiers in Laser Cooling, Single-Molecule Biophysics and Energy Science: Dave Weiss
Frontiers in Laser Cooling, Single-Molecule Biophysics and Energy Science: Dave Weiss
::2008/10/03::
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32
Frontiers in Laser Cooling, Single-Molecule Biophysics and Energy Science: Taekjip Ha and Xiaowei Zhuang
Frontiers in Laser Cooling, Single-Molecule Biophysics and Energy Science: Taekjip Ha and Xiaowei Zhuang
::2008/10/03::
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33
Frontiers in Laser Cooling, Single-Molecule Biophysics and Energy Science: Kurt Gibble
Frontiers in Laser Cooling, Single-Molecule Biophysics and Energy Science: Kurt Gibble
::2008/10/03::
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34
DIY CO2 Laser Tube Cooler
DIY CO2 Laser Tube Cooler
::2012/04/27::
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35
Laser printer Paper cooling
Laser printer Paper cooling
::2011/04/01::
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36
Laser Cutter 2.0 : Active Cooling System
Laser Cutter 2.0 : Active Cooling System
::2011/09/10::
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37
Laser cooling
Laser cooling
::2012/07/03::
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38
NIST Unscripted - Bill Phillips
NIST Unscripted - Bill Phillips
::2013/08/26::
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39
Laser Diode Cooling from Nextreme Thermal Solutions
Laser Diode Cooling from Nextreme Thermal Solutions
::2010/01/19::
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40
Phase separation in solid solution upon cooling: laser beam projection
Phase separation in solid solution upon cooling: laser beam projection
::2009/12/22::
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41
High Power Diode Lasers 35 W @ 915 nm + TEC, Water Cooling
High Power Diode Lasers 35 W @ 915 nm + TEC, Water Cooling
::2010/03/01::
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42
Bose-Einstein Condensate - Coldest Place in the Universe
Bose-Einstein Condensate - Coldest Place in the Universe
::2013/11/18::
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43
Keith Weninger, biophysicist
Keith Weninger, biophysicist
::2014/02/19::
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44
Magnetic Fields: Magnetic Cooling
Magnetic Fields: Magnetic Cooling
::2011/06/07::
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45
Biophysics of Sodium Channels, by Robert del Carlo (Honorable Mention 2013)
Biophysics of Sodium Channels, by Robert del Carlo (Honorable Mention 2013)
::2014/03/14::
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46
Мартин Вейс - Laser redistribution cooling
Мартин Вейс - Laser redistribution cooling
::2014/02/04::
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47
As cold as it gets
As cold as it gets
::2007/08/10::
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48
DIY DVD Laser w/ Cooling Fan
DIY DVD Laser w/ Cooling Fan
::2008/08/19::
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49
As Far As I Know: Can Shining a Laser on Something Cool It Down?
As Far As I Know: Can Shining a Laser on Something Cool It Down?
::2012/04/17::
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50
long pulse laser hair removal machine P-C03 with cooling head from jiatailonghe
long pulse laser hair removal machine P-C03 with cooling head from jiatailonghe
::2013/08/06::
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RESULTS [51 .. 101]
From Wikipedia, the free encyclopedia
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Laser cooling refers to a number of techniques in which atomic and molecular samples are cooled down to near absolute zero through the interaction with one or more laser fields.

Simplified principle of Doppler laser cooling:
1 A stationary atom sees the laser neither red- nor blue-shifted and does not absorb the photon.
2 An atom moving away from the laser sees it red-shifted and does not absorb the photon.
3.1 An atom moving towards the laser sees it blue-shifted and absorbs the photon, slowing the atom.
3.2 The photon excites the atom, moving an electron to a higher quantum state.
3.3 The atom re-emits a photon. As its direction is random, there is no net change in momentum over many atoms.

The first example of laser cooling, and also still the most common method (so much so that it is still often referred to simply as 'laser cooling') is Doppler cooling. Other methods of laser cooling include:

How it works[edit]

A laser photon hits the atom and causes it to emit photons of a higher average energy than the one it absorbed from the laser. The energy difference comes from thermal excitations within the atoms, and this heat from the thermal excitation is converted into light which then leaves the atom as a photon. This can also be seen from the perspective of the law of conservation of momentum. When an atom is traveling towards a laser beam and a photon from the laser is absorbed by the atom, the momentum of the atom is reduced by the amount of momentum of the photon it absorbed.

Δp/p = pphoton/mv = Δv/v
Δv = pphoton/m

Momentum of the photon is: p = E/c = h/λ
Suppose you are floating on a hovercraft, moving with a significant velocity in one direction (due north, for example). Heavy metallic balls are being thrown at you from all four directions (front, back, left, and right), but you can only catch the balls that are coming from directly in front of you. If you were to catch one of these balls, you would slow down due to the conservation of momentum. Eventually, however, you must throw the ball away, but the direction in which you throw the ball away is completely random. Due to conservation of momentum, throwing the ball away will increase your velocity in the direction opposite the ball's. However, since the "throw-away" direction is random, this contribution to your velocity will vanish on average. Therefore your forward velocity will decrease (due to preferentially catching the balls in front) and eventually your movements will entirely be dictated by the recoil effect of catching and throwing the balls.[1][2]

ηcooling = Pcooling/Pelectric

ηcooling = cooling efficiency

Pcooling = cooling power in the active material

Pelectric = input electric power to the pump light source

h/λ = p = mv

h = Planck's constant (h = 6.626∙〖10〗(-34) J∙s)

λ = de Broglie's wavelength

p = momentum of the atom

m = mass of the atom

v = velocity of the atom

Example: λ = h/mv = λphoton/x

x = number of photons needed to stop the momentum of an atom with mass m and at velocity v

Na atom

mNa = 3.818∙〖10〗(-26) kg/atom

vNa ≈ 300meters/second

λphoton = 600 nm

λphoton/x = h/(mNa vNa ) ⟹ x = 10372

Conclusion: A total of 10372 photons are needed to stop the momentum of one sodium atom with a velocity of about 300 m/s. Experiments in laser cooling have yielded a number of 10^7 photons to be emitted from a laser per second. This sodium atom could be stopped in space in just a matter of 1 millisecond.

Doppler cooling[edit]

Doppler cooling, which is usually accompanied by a magnetic trapping force to give a magneto-optical trap, is by far the most common method of laser cooling. It is used to cool low density gases down to the Doppler cooling limit, which for Rubidium 85 is around 150 microkelvin. As Doppler cooling requires a very particular energy level structure, known as a closed optical loop, the method is limited to a small handful of elements.

In Doppler cooling, the frequency of light is tuned slightly below an electronic transition in the atom. Because the light is detuned to the "red" (i.e., at lower frequency) of the transition, the atoms will absorb more photons if they move towards the light source, due to the Doppler effect. Thus if one applies light from two opposite directions, the atoms will always scatter more photons from the laser beam pointing opposite to their direction of motion. In each scattering event the atom loses a momentum equal to the momentum of the photon. If the atom, which is now in the excited state, then emits a photon spontaneously, it will be kicked by the same amount of momentum, but in a random direction. Since the initial momentum loss was opposite to the direction of motion, while the subsequent momentum gain was in a random direction, the overall result of the absorption and emission process is to reduce the speed of the atom (provided its initial speed was larger than the recoil speed from scattering a single photon). If the absorption and emission are repeated many times, the average speed, and therefore the kinetic energy of the atom will be reduced. Since the temperature of a group of atoms is a measure of the average random internal kinetic energy, this is equivalent to cooling the atoms.

Other methods of laser cooling[edit]

Several somewhat similar processes are also referred to as laser cooling, in which photons are used to pump heat away from a material and thus cool it. The phenomenon has been demonstrated via anti-Stokes fluorescence, and both electroluminescent upconversion and photoluminescent upconversion have been studied as means to achieve the same effects. In many of these, the coherence of the laser light is not essential to the process, but lasers are typically used to achieve a high irradiance.

Uses[edit]

Laser cooling is primarily used for experiments in Quantum Physics to achieve temperatures of near absolute zero (−273.15°C, −459.67°F). This is done to observe the unique quantum effects that can only occur at this heat level. Generally, laser cooling has only been used on the atomic level to cool down elements. This may soon change, as a new breakthrough in the technology has successfully cooled a macro-scale object to near absolute zero.[3] In 2011, a team from the California Institute of Technology and the University of Vienna became the first to use a laser to cool a miniature mechanical object to its quantum ground state.[4]

See also[edit]

References[edit]

  1. ^ Foot, Christopher (2005). Atomic Physics. Oxford University Press. pp. 178–180. ISBN 0 19 850695 3. 
  2. ^ Anissimov, Michael, and Bronwyn Harris. What Is Laser Cooling?. WiseGeek. Retrieved April 11, 2013, from http://www.wisegeek.com/what-is-laser-cooling.htm
  3. ^ Massachusetts Institute of Technology (2007, April 8). Laser-cooling Brings Large Object Near Absolute Zero. ScienceDaily. Retrieved January 14, 2011, from http://www.sciencedaily.com/releases/2007/04/070406171036.htm
  4. ^ Caltech Team Uses Laser Light to Cool Object to Quantum Ground State. Caltech.edu. Retrieved June 27, 2013, from http://www.caltech.edu/content/caltech-team-uses-laser-light-cool-object-quantum-ground-state

External links[edit]

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