Light Science... (Page 3)

Angry Beaver: Most of this science goes over my high school science, but I find it fascinating nonetheless

Evelyn99: A photon has no mass and like every other particle we don’t see them directly but take things away from them like positive changes

Evelyn99: A photon is probably invisible

Angry Beaver: How is the frequency of a photon/light measured? How long does such a measurement take?
Asked by: Torbjorn

Answer
It is not actually possible to directly measure the frequency of a single photon of light. This is because a single photon is going to behave more like a particle than a wave, and the concept of frequency (cycles or alternations per second) only applies to waves.

A spectrometer is a device that disperses the path of impinging photons through an angle that is dependent on their wavelength. In this way it is possible to closely estimate the wavelength of the photons.

The wavelength measurement is then used in a simple equation relating speed of a wave, its wavelength and frequency: frequency = speed / wavelength.

The speed of light is defined exactly as 299,792,458 m/s. A photon of red-orange light from a HeNe laser has a wavelength of 632.8 nm. Using the equation gives a frequency of 4.738X1014 Hz or about 474 trillion cycle per second.

A much more accurate method directly measures the wavelength of a laser beam by counting the number of fringes in an interferometer as one of its mirrors is moved over a very precisely measured distance.

A third and most accurate method measures the frequency of a laser by measuring the difference-frequencies produced by mixing it with a series of lower and lower frequency signals. (When two waves of different frequency are mixed, two new waves are produced with frequencies equal to the sum and the difference of the original frequencies.) The lowest or reference frequency and each of the difference frequencies is directly measured by comparing them with a frequency standard such as one of the atomic clocks at NIST. Described at: http://www.boulder.nist.gov/timefreq/ofm/synthesis/synthesi.htm

The time it takes to make a measurement depends on the method used and the accuracy desired. For the highest accuracy, measurements may take a second or more. A single photon wavelength measurement can be completed in a fraction of a microsecond, but the accuracy will be many orders of magnitude less.
Answered by: Scott Wilber, President, ComScire - Quantum World Corporation

Angry Beaver: This is interesting:

arnym: Y'know most of this stuff looks to me like scientists & mathematicians continually inventing new loophole and exception theories when it turns out that the ones they've dreamed up and relied on don't really work.

Angry Beaver: I think this one was an oldie which is not well known...that's what I get from his explanation anyway

Evelyn99: Well various ways but I know after watching a science program that using a laser beam that reflects through several mirrors that are placed in a space system depending on what you trying to do of course several computer systems monitors this they do much research this way and discover some interesting things about photons and how they react

Evelyn99: Remember there is a spectrum of different ways a photon and wave patterns a radio signal this message every X-ray taken are photons. What is interesting is that sometimes but not every time even with the same experiment photons actually do strange things like being two different places simultaneously

Evelyn99: Yes English is my first language but hard to write on this little thing. Why did you ask about light science when it seems that you know everything about it. That laser project was not wasted

Evelyn99: The agenda was to se how photons behave

Evelyn99: Well I don’t know much about light science but like to learn

Angry Beaver: That's a tad harsh arnym, evelyn is trying to express herself and her ideas here, not everyone is articulate and able to put an idea across in the written sense, yet they can articulate themselves well in person

arnym: Angry Beaver: That's a tad harsh arnym

Yes it is; thank you for the comment.

Evelyn I apologise. I've been frustrated about not understanding some of your posts, but I sense that you're a kind & gentle person and any frustration is my own to deal with.

I am sorry and I'll delete my most objectionable posts.

Angry Beaver: All cool man

arnym: Coolth is not something I'm often credited with but since you've offered the compliment I'll accept it .

Angry Beaver: Evelyn's been trying, give her credit for that

Evelyn99: Don’t worry))