physics of a laser?

userx

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Hmm...I'm taking physics this semester and my teacher was saying something on wavelength, and stuff. So I was just wondering....the equation for waves is velocity=wavelength*frequency so... for a green laser...velocity would be 300,000m/s since light travels at that speed. And the wavelength is 532nm with is I think...0.000532m. Soo if we plug those values in, we can determine the frequency, which turns out to be a whooping 563909774.4 cycles per second. Hmm...... did I do something wrong? It seems pretty big.. /ubbthreads/images/graemlins/confused.gif
 

Cornkid

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Your result is what we know it as 563.9 Megahertz or Mhz.
1hz = 1 cycle per second
I am also taking physics.(11th grade) I love it!
-tom
 

userx

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woww, cool. hmmm, so if we can somehow make the thing go a tad faster, it'll make the wavelength shorter...and we'll get blue and violet? Is it possible to change the frequency of a green laser?
(yup, 11th grade physics rocks)
 

PhotonWrangler

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That's better. If it was 563 megahertz, then the antennas on UHF walkie-talkies would light up when you keyed the mic! /ubbthreads/images/graemlins/smile.gif
 

Double_E

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Yeah, the speed of light is actually 3*10^8 m/s, or 300,000,000 m/s, also, a nano meter is 10^-9, so, 532 nm = .000000532 m. By the way, Physics ROCKS!!! You would have a hard time convincing me of a better field than Engineering/Physics/Mathematics
 

Amorphous

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Actually the formula is:

Speed of Light = Wave Length (lambda) X Frequency

1) Speed of light = 3x10^8 ( more precise = 2.99792458x10^8)
2) Lambda (wavelength) =532nm = 532x10^-9
3) Frequency = (What we want to solve)

Frequency = Speed / Lambda = 3x10^8 / 532x10^-9
= 5.639098x10^14
= 563.9098 Tera Hertz (not Giga Hertz)

(Note) Giga = 10^9

BTW, all the colors you can see with your eyes are between 384 Terahertz (Deep Red) and 769 Terahertz (pale violet).
 

Guliver

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Yep...thats exactly right...sorry meant Terahertz(tetra)
made the first mistake of using their speed of light figures...should know better..Of course visable light is Tera
Thank you for catching that.
 

SilverFox

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A question for you physics students...

The inverse square law states that light falls off (gets dimmer) with distance. This has to do with the divergence of the beam.

Lasers collimate the beam to try to minimize the divergence. This distorts the inverse square law until the divergence takes over.

My question is:

How do you measure the distance where the beam is no longer collimated and the inverse square law takes over?

Tom
 

Cornkid

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Im in high school, not in college.. but:

I did a little experiment and found that Laser beams do diverge at far distances depending on the frequency and power of the light.

Collimated laser beams, being parallel rays, maintain their power densities even at great distances.

To tell you the truth...I do not know how to find the distance where the beam is no longer collimated through mathematical equations... /ubbthreads/images/graemlins/confused.gif

-tom
 

mattheww50

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In a laser, some method is used to excite or pump up the electrons (usually it is electrical, but it can be chemical), and create an energy state population inversion. In normal life, all electrons are at the lowest energy level available. By exciting the electrons, it is possible to have large numbers that are at higher energy levels. The difference in energy levels between the excited state, and the next lower state or states determines the energy that will imparted on a photon produced when the electron drops down.If you can get enough of them to 'jump down' at once, you can produce enough photons to be significant, and if you are real smart, you can produce very high energy densities in the 'beam' to make a weapon. Quantum mechanics dictates that these energy levels are discrete, as a result the difference between energy states change can produce one and only 1 energy level in the photon, only a single energy level photon can be produced. According to Physics the energy of a single photon is E=hF, where F is frequency, and h is Plank's constant.


F or frequency must be constant, since we can only have one energy, and plank's constant is just that, a constant.

As a result, by choosing the materials to make the laser out of, you can shoose the available excited electron energy states.
He-Ne will produce a red laser, because the differences between the energy states, the dropping down of the electron produces photos that correspond to a red. Other combinations can produce differing excited electron energy states, and can produce other colors. Carbon Dioxide produces Infrared,I believe Argon can produce Green. Ruby (chromium dopped aluminum oxide) also produces red. By picking the right materials with the right population dynamics you can produce almost anything in the Electromagnetic spectrum from Mirowaves to Ultra violet. A photon in the visible light spectrum is on the order of 1 electron volt.
 

herminator

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I've been having some trouble with my leadlight green laser resently...

Does the diode run on a constant stable DC voltage, or does it run on a varying DC voltage?

I wonder if I can connect the diode directly to a DC power supply (with adjustment for maximal current of cause..)
 

SilverFox

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I guess nobody knows anything about divergence...

Reading about pilot safety, it seems that they consider the danger zone out to about 1000 feet. Beyond that, I guess the beam divergence is great enough to eliminate the safety hazzard.

From this bit of data, we may be able to say that beyond 1000 feet, the inverse square law begins to takes effect...

Tom
 

bootleg2go

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From what I've read, the inverse square law will always apply. Since it applies in astronomy to a point light source like a star, it would apply to a laser even with a very small divergence. It could be that the divergence of the laser will even add to the inverse square law though.

Jack
 
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