--------- #1355 - Laser Light is Cool
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- One of the first toys I can remember getting for Christmas was an “ Erector Set” It was dozens of metal strips with holes in them. Hundreds of little screws and nuts. Maybe a couple pulley wheels. And, you could make all kinds of things, Ferris Wheels, Windmills, box cars, robots, whatever your imagination could come up with.
- I also remember another toy. It was a clear light bulb with a black and white fan inside. The fan would spin when you shinned a light on it. the white side reflected the light and the black side absorbed the light and the fan would spin.
- Light is supposed to be massless. Without mass there is no Kinetic Energy =
½ M* v^2. Photons are massless, yet, they carry energy and they can move things.
- It was in 1619 the Johannes Kepler suggested that the pressure of sunlight caused the comet tails to always point away from the Sun.
- In 1746 Leonard Euler wrote the equations for how waves in motion produce pressure.
- In 1873 James Clerk Maxwell calculated that bright sunlight would put a pressure on Earth equal to 4 pounds per square mile.
- My toy light bulb invention first occurred in 1873. Again the pressure of light was what caused the mill to rotate. It was called a “ light mill”. Science has since concluded that it was more caused by the transfer of heat by the light reflecting and absorbing on opposite sides of the fan. The expanding heat from the black absorbing side caused the fan to spin.
- Today science is still experimenting with light pressure. Science is trying to use light pressure to cool objects by slowing down the vibration of atoms. The goal is to reach Absolute Zero temperatures and the ‘Ground State” of atom vibrations. The new science is called “ optomechanics“.
- The reason science is interested in Absolute Zero is that large objects reduced to their Ground States of lowest energy will display the properties of Quantum Mechanics. Large objects near Absolute Zero begin behaving like sub-atomic particles.
- We think of sunlight as heating things not cooling things. Our intuition tells us that light should not be cooling things down? Temperature is vibrating atoms. A very small force that opposes each cycle of vibration will slow down the vibration and make it cooler. Vibrating atoms is the definition of Thermal Energy, “ heat”. When vibrations slow down, atoms cool down.
- Maxwell’s calculations in 1873 showed that sunlight reflecting on one square meter of mirror delivered a pressure of 1/1000 the weight of a small paper clip. A very small force but enough to cool atoms.
- If a laser light is tuned just off the resonant vibration of an object it will dampen the oscillations. It will steal a small amount of vibrational energy. The vibrating object cools down.
- In 2006 science first used the technique to cool mirrors down to 10 degrees Kelvin. Getting to 0 Kelvin means removing every “quanta” of energy that is in the oscillations. Energy, like the photons, comes in “ quanta”, discrete packets of vibrational energy. The energy of one photon packet is Planck’s Constant of Action = 1.05*10^-34 Joule*seconds. That is the energy of one cycle of oscillation. Multiply this times frequency of oscillation and you have the Energy of the wave of oscillation.
---------------------- E = h * f
- In 2009 science used microwave light to cool a vibrating object down to 4 quanta of thermal energy. This meant the object’s atoms were in Ground State 21% of the time. We could almost begin to study the effects of Quantum Mechanics.
- In 2010 UC Santa Barbara used a ceramic wafer 30,000 nanometers long that vibrated in resonance at 6,000,000,000 times per second. The theory being that the faster an object quivered the easier it would be to remove its energy. The result was to put the ceramic wafer in its Ground State 93% of the time. The wafer could be put in a state of “Superposition”, both moving and still at the same time.
- Science as since gone beyond the microscopic world an successfully cooled a giant 10 kilogram mirror down to 234 quanta. these mirrors are being used as gravitational wave detectors in the OLGO project.
- Another gravitational wave detection project in Italy uses an aluminum bar weighing 2,000 pounds that was cooled down to 4,000 quanta.
- Electromagnetic radiation consists of “ quanta ‘ of energy. Each quanta is an identical indivisible unit equal to Planck’s Constant * frequency.
------------------------ E = h * f
- The momentum of light, “p”, is mass times the velocity of light. “c” is the velocity of light.
------------------------- p = m * c
- Energy is equal to momentum times velocity.
----------------------- E = p * c
---------------------- E = m * c^2
- Wavelength of light times the frequency of light equals the speed of light.
---------------------- w * f = c
-------------------- w = E / c = h*f / c = h*c / E = h / p
- All of these are “ quanta ’ for a single cycle of oscillation or vibration. When the quanta get down to a single wavelength , quanta = 1, it is as cold as it gets. Hope you like this review. And, hope I can make an announcement of gravity wave detection using those cold mirrors. This would be a new form of “ light” for astronomers to explore the Universe.
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707-536-3272, Sunday, December 18, 2011
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