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Laser Doppler
How can a laser be used to cool an object... where'd the entropy go?
You may be aware of laser cooling. And if you are, you might even be aware of the idea of Doppler cooling, where a series of photons are used to reduce the momentum of an atom or other object. But here's the question: how can a laser beam, which is concentrated source of energy, be used to remove energy from an atom? The colder an atom becomes, the less entropy it has. Where is the entropy going? Is this a violation of the second law of thermodynamics? Why isn't the laser just heating the atom up? And while we are at it, could laser cooling be done with a different source of light, say from a collection of incandescent light bulbs?
Of course it is possible to reduce the temperature in one part of a system at the expense of
increasing the entropy in another part of the same system. It is done all the time in a household
refrigerator. The refrigerator removes heat from one part of the system (the interior cabinet) and
dumps it via the rear coils into the room air, with a increase in entropy at that point.
The same thing happens in the case of laser cooling: the laser removes momentum from the
atoms of a gas, reducing their overall kinetic energy and thus their temperature, at the expense
of the energy being used to run the laser which dumps a bunch of heat into the air (where entropy
is increasing). Don't make the mistake of thinking of only one half of the overall system as an
isolated process.
Why isn't the laser heating the atoms up? If you already know the details of how laser cooling
works, you know that the conditions, the laser tuning, and the gas are specially set up for it to work
that way. But there is no magic or violation of entropy going on. It is just a case of reducing the
entropy within the confines of one part of the system, at the expense of increasing it in another
part of the system which we aren't concerned about.
It would not work with regular incandescent lights, because laser cooling requires the kind of
specific single wavelength light that only a laser can provide.
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Optodyne VS-5101 Laser Doppler Displacement Meter Vibration Sensor+LD47B/LDDM |  |
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US $3,999.99 | 26d 11h 2m |
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MOOR INSTRUMENTS DRT4 LASER DOPPLER TEMPERATURE MONITOR v4.2 | |
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US $1,999.00 | 26d 20h 10m |
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Laser Doppler and Phase Doppler Measurement Techniques | |
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Laser-Doppler Blood Flowmetry NEW by A. P. Shepherd | |
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LDA Application Methods: Laser Doppler Anemometry for Fluid Dynamics by... | |
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Dantec Dynamics Laser Doppler Anemometry System: LDA | |
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Dantec Dynamics Fiberflow 2D 60mm Probe LDA Laser Doppler Anemometry System | |
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Optodyne VS-5101 Laser Doppler Displacement Meter Vibration Sensor+LD47B/LDDM | |
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Summit Doppler Hand-held Doppler Carrying Case $26.34 Features of the Summit Doppler Hand-held Doppler Carrying Case:A convenient lightweight carrying case for all of Summit Doppler's hand-held Dopplers. |
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Summit Doppler Hand-held Doppler Universal Clamp $207.48 Features of the Summit Doppler Hand-held Doppler Universal Clamp:A heavy duty table or cart clamp for all of Summit Doppler's hand-held Dopplers. |
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Summit Doppler Rechargeable Battery for Rechargeable Doppler Systems, 3/pk $20.21 A package of 3 rechargeable batteries for all of Summit Doppler's rechargeable Doppler systems. |
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Summit Doppler TableTop Doppler Stand with Storage Basket $262.61 Features of the Summit Doppler Stand:A sturdy 5 castor stand for all of Summit Doppler's table-top Dopplers with convenient storage basket. |
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Summit Doppler Alkaline Battery for Non-Rechargeable Doppler Systems, 3/pk $9.9 A package of 3 AA alkaline batteries for all of Summit Doppler's non-rechargeable Doppler systems. |
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Summit Doppler Hand-held Doppler Stand without Storage Basket $207.48 Features of the Summit Doppler Stand:Sturdy 5 Castor Stand for Summit Doppler's Handheld Dopplers. |
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Summit Doppler TableTop Doppler Stand without Storage Basket $207.48 Features of the Summit Doppler Stand:A sturdy 5 castor stand for Summit Doppler's Tabletop Dopplers. |
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Summit Doppler Stereo Headphones for Dopplers $17.11 Features of the Summit Doppler Stereo Headphones:Stereo headphones used with all of Summit Doppler's hand-held and table-top Dopplers. |
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Vestal Doppler Watch $180 Vestal Doppler Watch: The Vestal Doppler Watch has a one-of-a-kind, multi layer stainless steel bezel surrounded by a bullet-proof case design. Its unique hinging lugs helps the Vestal Doppler Watch fit comfortable on almost anyone. As easy on the wrist as it is to tell time. |
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Summit Doppler Hand-held Doppler Stand with Storage Basket $262.61 Features of the Summit Doppler Stand:A sturdy 5 castor stand for all of Summit Doppler's hand-held Dopplers with convenient storage basket. |
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Doppler Radar And Weather Observations $44.51 Geared toward upper-level undergraduates and graduate students, this book reviews the principles of Doppler radar and emphasizes the quantitative measurement of meteorological parameters. It illustrates the relation of Doppler radar data and images to atmospheric phenomena such as tornadoes, microbursts, waves, turbulence, density currents, hurricanes, and lightning. 1993 edition. |
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Ogio Doppler Luggage $21.95 Ogio Doppler Takes care of your toiletries and accessories while you're away from home. Features Top webbing carry handle Swivel hook for easy mount Multiple compartments for toiletries and accessories |
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Lecture-28-Hot Wire Anemometry and Laser Doppler Velocimetry
what is the difference between police radar and police laser? They are both used as speed detection equipment
I believe they work on different principles, such as the Doppler principle. Don't think that applies to laser
No, Lidar doesn't use Doppler frequency shift techniques. Instead, it sends out a number of pulses very quickly and measures the return time for each. This gives a series of distance measurements over a short period of time, which the Lidar CPU then uses to calculate speed.
Yes, police radar works on Doppler frequency shiftng of the return pulses.
More details for both radar and lidar may be found here: http://auto.howstuffworks.com/radar-detector2.htm
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