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Lasers - HSN forum

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Lasers


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#1 The Wedge Effect

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Posted 23 May 2005 - 09:00 PM

I really need help on lasers, the teacher gave NO notes on them. sad.gif

Anyone direct me to some note please? blink.gif ph34r.gif

#2 Phoenix

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Posted 23 May 2005 - 09:23 PM

Wedge, one thing they might ask you is why there's parallel mirrors and why one of them is fully silvered, whereas the other is partially silvered. They are parallel to ensure that only photons travelling in an exact straight line down the middle are reflected back, which leads to a more intense laser. I wasn't sure about the partially silvered part, but my teacher told me it was simply to allow some of the particles to escape.

Are you also short on notes for Stimulated emission/spontanious emission?

#3 dfx

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Posted 23 May 2005 - 09:31 PM

The laser consists of two parallel mirrors. One is partially reflecting and allows only 1% of the light through while the rest of the photons are reflected back.

Stimulated emission of radiation is essentially passing a photon of energy hf = to the difference between the two energy levels W2-W1. So you end up with the incident photon and stimulated photon which are both in exactly in phase.



#4 drew_jarvie

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Posted 23 May 2005 - 09:31 PM

QUOTE(Wedge37 @ May 23 2005, 09:00 PM)
I really need help on lasers, the teacher gave NO notes on them. sad.gif

Anyone direct me to some note please?  blink.gif  ph34r.gif

View Post



Not really much on them. You just need to know that the electrons initially move to a higher discrete energy level to begin with by gaining energy from the lasing material.

Some then SPONTANEOUSLY EMIT photons by randomly "jumping" to a lower energy level.

These will trigger other photons by STIMULATED EMISSION where an incident photon directly causes an electron to jump down a level. When this happens, another photon is created with:

-The same energy as the energy jump
- Monochromatic (all photon have same frequency)
- Coherent (all photons are in phase)
- Intense ( all photons are in phase and concentrated inot a small area [this is why even really weak lasers can cause retinal damage-they have such small cross-sectional areas])
- Parallel due to the mirrors (only light striking the mirrors at 90 deg is reflected and ampified


Hope this helps






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