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------------ 2751 - LIGHT - Interferometers
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- Photons behave both as waves and as particles. So do atoms. So does everything. It is just that in a larger mass the waves are too small to be detectable. You have to get to small masses, atomic size, and that is when waves become predominant.
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- Light interferometers were invented over 200 years ago. Just recently science has began using this old technology in new ways. Radios have been around a long time too. They are everywhere today. Your cell phone is a radio. Your remote control is a radio. AM and FM radios operate at frequencies of 1000 kilohertz and 300 Megahertz.
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- These frequencies correspond to wavelengths of 300 yards down to 4 inches. The TV remote uses infrared waves that have wave lengths of 0.000001 meters, which is about the size of a bacteria.
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- Radio waves and light waves are the same electromagnetic medium as radio waves, why don’t we have radios that operate at light wave frequencies? In fact ,we do, and simple ones are operating in fiber optic cables.
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- Science is learning how to use light wave frequencies to build comb generators, and heterodyne mixers that are very analogies to traditional radios. The frequencies are 10^15 cycles per second, 1,000,000,000,000,000 oscillating cycles in each second. This corresponds to wavelengths of 3*10^-7 meters, 0.0000003 meters.
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- The light wave interferometer is one of the most accurate instruments known. The new comb generators will make them more accurate then today’s atomic clocks. A radio’s simple comb generator generates a comb of harmonic frequencies by pulsing energies into a simple diode. The rapid on and off pulse is a square wave containing all the harmonics of the original signal.
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- The optical comb generator does the same thing only at light frequencies. Using these optical comb generators will allow more precise atomic clocks to be invented. Also, there will be new ultra sensitive chemical detectors. Lasers will control chemical reactions. Higher capacity telecommunications will be possible at higher frequencies. Improved light detectors and light range finders will be invented. And, there will be more applications that we have not thought of yet.
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- Optical Comb generators start with mode-locked lasers that can create ultra-short pulses of light. The shortest pulses from these lasers have durations less than 10 femtoseconds. ( See Review 361 “Time is Getting Short”). ( Review 912 “Wave-Particle Duality“).
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- The carrier frequency for the light consists of one pure frequency, or color. The amplitude pulse of this single frequency consists of light of many frequencies all traveling together. The shorter the pulse, the broader the spread of frequencies.
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- The mode-locked laser is set to emit a train of these pulses at a regular rate, called the Repetition Frequency. If you plot these frequencies the spectrum appears as the teeth on a hair comb, spaced precisely at the laser’s Repetition Rate.
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- Typically the repetition rate is set at 1 GHz, or 1,000,000,000 cycles per second. The optical comb has 400,000 teeth spaced out at 1 GHz apart. High-speed photodiodes can accurately measure frequencies at 1 GHz. Now, with this optical comb we can translate the accuracy up into the frequencies of light.
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- One problem that had to be overcome was the phase shifting that occurred with a train of pulses. This amounted to creating an Offset Frequency after a multiple of pulses. Scientists had to know this Offset Frequency in order to calibrate their instrument for ultra-precise measurements.
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- Using a cesium beam atomic clock one second is defined as a cesium oscillation of 9,192,631,770 cycles, exactly. A cesium clock is based on 9 GHz microwaves being absorbed by cesium atoms. An optical comb generator could be calibrated to 60,000 times the cesium frequency.
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- To calibrate out the Offset Frequency the scientists needed a mode-locked laser that had a bandwidth of at least one octave. An octave is a factor of 2 in frequency. An octave spanning spectrum enables the comparison of frequencies of two comb lines at opposite ends of the spectrum.
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- Any deviation from the second frequency being exactly twice the first frequency is a measure of the phase shift and the Offset Frequency. This is called self-referencing because you are comparing the comb frequency against itself. If these two frequencies are mixed together, or beat together, the difference frequency is the Offset Frequency, and this process is called “heterodyne detection“. The same as in an old heterodyne radio.
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- We have just begun to explore the potential of optical comb generators so expect many new discoveries using this powerful tool in the hands of graduate students.
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- Another new tool is the atom interferometer. It is similar to the light interferometer except it uses the waves from atoms instead of the waves from photons.
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- Gyroscopes using this system will improve 200 fold. This will allow navigation cross country that is more accurate than GPS. Interferometers use interference patterns from mixing two waves to calculate the differences in the distances that the two waves travel.
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- In the 1890’s Albert Michelson and Edward Morley tried this experiment to detect if Earth’s orbit was passing through an ether. Science at that time thought that an ether medium was needed for light waves to travel across space. They discovered there was no ether.
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- In 1920 Louis-Victor de Broglie discovered that all particles behaved as waves depending on the particles mass and its velocity. The heavier and faster the particle the shorter its wavelength. An atoms wavelength is around 1/100th of a nanometer. Visible light has wavelengths of 400 to 700 nanometers. If the path of an atom varies 1/1000th of a nanometer an atom interferometer can detect it. To detect these waves of atoms they must be cooled to nearly absolute zero Kelvin.
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- On the Earth’s surface, gravity’s acceleration is 9.8 meters / second. But, this varies slightly depending on the composition of the rock at the surface. By detecting the variations in the strength of gravity these instruments can detect underground oil.
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- 100,000 tons of oil buried 1 kilometer underground will decrease gravity by a few hundred thousands of a percent. Not just oil. The same technique can detect underground diamonds. Not just diamonds, The atom interferometer can detect underground caves where terrorists are hiding. However, the most immediate use will be the military using it for accurate navigation without the use of satellites. They can even navigate under the Artic ice with precision.
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- In astronomy we can put light and atom interferometers in space to be used to detect gravity waves. Gravity waves radiate from binary Black Holes and binary Neutron Stars. These gravity wave “telescopes” could see back to the beginning of the Universe.
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- The Cosmic Microwave Background allows us to see back to 300,000 years after the Big Bang. But, gravity waves could see past that opaque wall even further back in time to the Big Bang. Whenever you have a greater ability to see, you are bound to see something new.
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- Light interferometers and atom interferometers are ultra-precise measurements that will discover new things. Get ready to learn.
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------------------------------------ Here are more Reviews about light:
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- 2684 - LIGHT - keeps getting stranger? We have wave- particle duality, photon entanglement and anti-matter, matter asymmetry as three courses in our college of future study. Entanglement bothers me the most. My imagination can wade through the other two, but not that one. It is just too weird for me to comprehend. Entanglement in the brain? Here is a Review for you to try it.
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- 2683 - LIGHT - the wave-particle duality? - At the time of Isaac Newton in 1687 science considered light to be a beam of particles. In the 1900’s some experiments measuring interference and diffraction concluded that light was indeed waves. Interference is when two waves come together and the beams amplify or cancel each other out depending on how the phases of the waves are intersecting. So, when did light become particles again?
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- 2661 - LIGHT - What It Means To Be Visible? If something is visible it usually means that your eyes are sensitive to the electromagnetic radiation they are receiving. Of course, other detectors besides eyes can be used to detect a much wider range of electromagnetic radiation.
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- 2609 - LIGHT - how to measure its speed ? One of the most common questions asked is whether gravity is instantaneous, or whether there’s a speed limit to how fast the force of gravity can travel. This is not as simple a question as it seems on the surface. Most would say at the speed of light. However the problem with the speed of light, is it gets here too early in the morning.
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- 2537 - LIGHT - stranger than you can imagine? - Is “light” energy what is warping space and time? What about Dark Energy that is the repulsive force expanding space in the Universe? Is “light” responsible for this as well? “Light” has a much bigger role to play in the Universe than what we can “see”. All that we do not see is stranger still.
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- 2402 - LIGHT - There is not enough light. We can never understand the Universe by studying starlight. There is just not enough of it. Starlight comes from the energy, or radiation, from ordinary matter and ordinary matter comprises less than 5% of the Universe. 30% more is Dark Matter and 65% more is Dark Energy. We need a telescope that can see in the ”Dark”.
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- 2387 - LIGHT - how light moves particles. Einstein had developed the theory of special relativity that revolutionized the way we understand light. To this day, it provides guidance on understanding how particles move through space.
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- 2310 - Getting Light from Electricity and Magnetism. Light, electricity, and magnetism seem to me to be three separate things. How can they be connected into electromagnetic waves? We had to discover each one at a time before Einstein even connected them with mass and space.
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- 2306 - How far away is the Sun? When at sea how can we use the Sun to determine our position, longitude and latitude? How can the moons of Jupiter be used as a clock? How can that clock be used to determine the speed of light? Learn from Ole the Danish astronomer:
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- 2210 - There is a star that is looping around the blackhole at the center of our galaxy. Theory of Relativity tells us that light would loose energy leaving a gravity well and it would gain energy entering the gravity well. This energy difference shows up in the change in wavelength of the light. Einstein’s math is tested again.
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- 2260 - Getting light from electricity and magnetism? How do the electric and the magnetic forces, or, waves create light. Or, is it the opposite? Is light that creates the electric and magnetic forces? See here, to learn the answer.
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- May 3`, 2020 915 2751
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----- Comments appreciated and Pass it on to whomever is interested. ----
--- Some reviews are at: -------------- http://jdetrick.blogspot.com -----
-- email feedback, corrections, request for copies or Index of all reviews
--- to: ------ jamesdetrick@comcast.net ------ “Jim Detrick” -----------
- https://plus.google.com/u/0/ -- www.facebook.com -- www.twitter.com
--------------------- Monday, June 1, 2020 -------------------------
-----------------------------------------------------------------------------------------
-
- May 3`, 2020 915 2751
----------------------------------------------------------------------------------------
----- Comments appreciated and Pass it on to whomever is interested. ----
--- Some reviews are at: -------------- http://jdetrick.blogspot.com -----
-- email feedback, corrections, request for copies or Index of all reviews
--- to: ------ jamesdetrick@comcast.net ------ “Jim Detrick” -----------
- https://plus.google.com/u/0/ -- www.facebook.com -- www.twitter.com
--------------------- Monday, June 1, 2020 -------------------------
-----------------------------------------------------------------------------------------
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