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Are diode lasers real lasers?

Skans

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Here's something that is probably obvious to many here, but not to me which I am having a difficult time understanding. I sort of understand how light amplification takes place with a ruby rod, a mirror, a semi-reflective mirror and a light source as a pump to create a narrow beam of coherent light.

But, these laser diodes seem to be nothing more than a very bright light source that can be focused into a narrow beam of light using lenses. Is there any real amplification of light taking place within the diode itself?
 

diachi

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Here's something that is probably obvious to many here, but not to me which I am having a difficult time understanding. I sort of understand how light amplification takes place with a ruby rod, a mirror, a semi-reflective mirror and a light source as a pump to create a narrow beam of coherent light.

But, these laser diodes seem to be nothing more than a very bright light source that can be focused into a narrow beam of light using lenses. Is there any real amplification of light taking place within the diode itself?

It's basically exactly the same thing as the ruby rod with mirror(HR, high reflector)/semi-reflective mirror (OC, output coupler) and flash lamp. Except much smaller and pumped by electricity instead of light. You still have the HR/OC/Gain Medium/Pump Energy etc.

So yes - they are real lasers - if they weren't they wouldn't be called lasers...

Edit: This is broad generalization/simplification of how laser diodes work of course, but the principles are much the same.
 
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Skans

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At the risk of sounding stupid here, if a diode laser is "pumped" with electricity and not an amplification of light, then isn't it really something else that simply produces results similar to that of a Laser? Also, without a lens to collimate the light coming from the diode, doesn't the light simply diverge from its source just like any other light source? In other words, doesn't a naked laser diode produce a big ball of scattered light?
 

ElectricPlasma

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I've thought about this but never really said anything

+rep Skans, I'm in for the answer of this too.

But laser diodes produce uni-directional light, it's not just raw light - it's easy to collimate because of it's singular direction.

I guess if you would consider the definition of a laser strictly as light amplification, then it's not necessarily a laser. But in reality lasers have gained much more of a definition than that, it's a tightly collimated beam of light which is what's produced by a laser diode and lens/optics.

If you think about it, the same thing could be applied to a flashlight with a really nice reflector, so I'm not quite sure.
 

diachi

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At the risk of sounding stupid here, if a diode laser is "pumped" with electricity and not an amplification of light, then isn't it really something else that simply produces results similar to that of a Laser? Also, without a lens to collimate the light coming from the diode, doesn't the light simply diverge from its source just like any other light source? In other words, doesn't a naked laser diode produce a big ball of scattered light?
The "pump" is just the source of energy that excites the gain medium, where the "Light Amplification by Stimulated Emission of Radiation" action occurs. It doesn't need to be light, nor does it need to be electricity, there's a lot of energy sources that are used for various different lasers. Gas Dynamic Lasers use the combustion of a gas as the "pump" source for example. IIRC, last I watched Styro's YouTube channel he's planning on experimenting with explosively pumped lasers.

The pump "excites" the gain medium, which emits its own light which is then amplified. Again ... that's a bit of a simplification, but it gets the point across.

Yes - without a lens of some sort the output from a diode laser is going to be highly divergent - although all laser light diverges from it's source, there is no such thing as a perfectly parallel beam of light. What separates the light emitted by laser diode from say an LED is that the output of a laser diode is both coherent and monochromatic - both key properties of laser light.


Read this if you don't understand how a laser works completely: How do lasers work? | Who invented the laser?

Understand each part of the acronym LASER - Light Amplification by Stimulated Emission of Radiation.
 
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Rivem

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To expand a bit on the actual mechanics of a diode laser, electricity causes something called population inversion of the electrons, and this is the critical part of stimulated emission (laser).

Basically, the semiconductor material works almost identically to LEDs except for the fact that the electrons in the material will hang around in an excited state while the bandgap (caused by two semiconductors) is charged. This makes a laser diode's bandgap into both an LED and a gain medium.

Light is emitted by electrons changing their levels, and the population inversion puts all of the electrons in the medium into a high state that only allows them to fall when hit by an incoming photon. The fall that these electrons undergo usually involves the same amount of energy as the semiconductor badgap, so the LED and stimulated emission produce the same wavelength of photon. This is where the mirrors come in to make a laser.

The mirrors force light through the gain medium in roughly one direction. Because of this, some photons bounce back and forth through the diode, forcing more photons to be emitted in the same direction and so forth. What comes out of the emission end(s) is a large amount of highly directional light that is also quite coherent (same wavelength/frequency).

This electrical pumping is also roughly the same case with most gas lasers without the semiconductor part.

Really, pumping a laser just means causing a population inversion of electrons which can be caused by electricity, light, heat, chemistry, and a lot more physical processes that involve electric charges.

Edit: It admittedly is a lot more complicated than that, but I'm uncomfortable taking it too far since I'm not done with my E&M/quantum physics until next year. Plus, it's summer break :p.
 
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I want to thank you all for the brief education. I didn't quite understand it, i've read it before but never was it explained like I'm 5. Thank you for that.
 

WizardG

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One of the keys to the operation of a laser is the population inversion. Below the threshold current a laser diode is just a fancy LED. As the current through the diode is increased there comes a point where the concentration of high energy charge carriers is high enough that actual Amplification of light can occur, i.e. the charge carriers start 'cooperating' to not just randomly radiate photons but team up to lase. The situation is the same in any laser. Below a certain current a helium neon laser is just a fancy neon sign. Cross the threshold where you get a population inversion and the thing starts to lase instead of just emitting photons randomly in all directions.
 
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Rivem

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I realize it's pretty hard to understand, so I've compiled some fairly short and simple videos. There's overlap, but I recommend you watch them in order. Here they are to help you visualize:

Good video on basics of lasers:

More on quantum performance of lasers:


HeNe demo:


Diode laser construction:

 

Skans

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I actually thought the last video was the best at describing how a diode lases. I'm convinced - the diode laser is a true laser!
 

Rivem

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I actually thought the last video was the best at describing how a diode lases. I'm convinced - the diode laser is a true laser!
Glad I could help. :beer:

I included the other videos to build up the basic mechanics that make lasers lase before the diode mechanics.
 
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I want to thank you all for the brief education. I didn't quite understand it, i've read it before but never was it explained like I'm 5. Thank you for that.
And I add my thanks too. I've gained a little better understanding of the lasing process.

Ed
 

Pman

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Or in other words:

Laser = Magic

+Rep to who I can for this;) I don't think I've ever seen that question before.
 




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