Can anyone enlighten me to the magic of lasers.

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The_Silntdoogood
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Can anyone enlighten me to the magic of lasers.

Post by The_Silntdoogood » Tue Nov 22, 2011 9:53 pm

Before I get started, I will admit, in the long run, I'd like to get a burning project completed, but please don't let me come off as a 14 year old pyromaniac. Precautions will be taken, and I have several schematics for a lockout mechanism when it gets out of my possession. Primarily, I would like to know more about lasers, not just a parts list to pop a balloon form 20 feet away.

With that being said, I would like to know general basics. Links would be acceptable. Google tends to throw me fuzzy pictures of some kid playing with a potentiometer.

If anyone can help define mW, and nm for me with a little more than a one line text book definition, along with explain the necessity for a driver board, and what it does. Is there a more specific name to it? I have worked with other projects, that required "drivers", upon further inspection, it was just an inverter, and I salvaged one from a scanner. I doubt the same scanner inverter is going to power a laser without killing it.

How to the specifications of the driver boards correspond with the specifications of the diodes?

Thanks
-Spence

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evilteddy
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Re: Can anyone enlighten me to the magic of lasers.

Post by evilteddy » Wed Nov 23, 2011 10:51 pm

I could talk about how the lasers produce coherent light by stimulated emission in a gas being excited into their third principal quantum state by an EM wave of super visible frequencies but I can see that that's not what you want here.

So the mW and nm are both units meaning milliWatts and nanometres respectively. In the case of lasers mW refers to the power being outputted from the laser in the form of light. Not the power that the laser diode consumes but the intensity of the laser produced. For anything above 5 mW you should definitely have eye protection. The nanometres is referring to the wavelength of the light. The shorter the wavelength the higher its frequency (wavelength = speed of light/frequency). Obviously light is part of the EM spectrum so you start from 720nm with red light and end at 370nm with purple and you can see the order of them on any plot of the em spectrum: linky link. From this you know that if you were told a laser had the specs of 10mW and 540nm then its a fairly powerful laser that you'd need eye protection from and that it's green.

As for the driver circuit like many high powered LEDs a laser diode will draw too much current and kill itself given the chance. Driver boards are pretty much just a voltage regulator to control current flow with a couple of nice things put on them like a pot to control intensity of the laser. This page says it better than I ever could.

Hope that helps.

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The_Silntdoogood
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Re: Can anyone enlighten me to the magic of lasers.

Post by The_Silntdoogood » Thu Nov 24, 2011 2:05 pm

evilteddy wrote:I could talk about how the lasers produce coherent light by stimulated emission in a gas being excited into their third principal quantum state by an EM wave of super visible frequencies but I can see that that's not what you want here...

Actually, I wouldn't be against some information along those lines too. I'm trying to work my way down the Wikipedia page, but it's a lot of information to take in at once.

The last link looks to be exactly what I was looking for, and thanks for the relating the units!

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evilteddy
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Re: Can anyone enlighten me to the magic of lasers.

Post by evilteddy » Sat Nov 26, 2011 1:27 am

Well I don't know how much physics you know so I'll try and keep it fairly basic. Laser is an acronym for Light Amplification by Stimulated Emission of Radiation. What does this mean? Well the most important part to understand is the concept of stimulated emission and how it produces coherent light. When I'm talking about coherent light I'm referring to light which is in quite well in phase (where the wavelengths line up) and travelling in the same direction. These two properties give laser light their extraordinary characteristics.

Back to stimulated emission though, say we had a material which you could excite with some kind of energy (let's say its a crystal) which would release a bit of heat then stay mostly excited. Now eventually the atoms in the crystal randomly emit light and this makes them unexcited again but we choose a material where this process tends to happen slowly. The crystal we have chosen exhibits the property of being suitable for stimulated emission which means that when a photon (the smallest bit of light you can have) passes through the crystal it will soon encounter one of the atoms you have excited and when it does it makes the atom emit a bit of light and become unexcited as above. The cool thing is that now you have two photons of light travelling in the same direction with the same wavelength (which is colour). So now we have a way of making pulses of coherent light. We excite a crystal, when one of the atoms randomly emits light it travels through the crystal gathering more photons and making a bit of a laser. Cool.

Unfortunately this way will only give you really small and weak pulses. You improve this by putting the material in a tube with both ends as mirrors, the trick being that one of the mirrors is semi reflective. Now when your pulse of light exits the crystal it will be reflected back through the crystal and soon we'll have a continuous stream of coherent light bouncing between the two mirrors with a proportion going through the semi reflective one and outside into the real world as your laser!

For a visual example see this small java thing. Depending on your level of physics knowledge ignore the graphs on the right and just look at how the stimulated emission builds up a resonant stream of light.

Hope that helps.

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