# Increasing laser power

1. Jun 23, 2004

### relativelyslow

if you take a laser and shine it into another set of mirrors so that the light shoots out of the opposite end through which the laser first went into the second set of mirrors, would it be more powerful than when it started (the second set of mirrors would have a lasing medium)? if so, could you do this infinitely for infinite power?

2. Jun 23, 2004

### Treatz

No, this will not work. you can not create more light, you can also not destroy the light. the light there is will all there ever will be, and it will eventually diverge so it is not visible at all.

3. Jun 23, 2004

### relativelyslow

wouldn't you be creating more light by exciting the second lasing medium (sort of shining two lasers in one beam)?

4. Jun 23, 2004

### Integral

Staff Emeritus
If the return beam is out of phase with the beam in the cavity you could well lose power (this is the most likely event). If the lasing medium is already maintaining the maximum level of pumped atoms (maximum population inversion) there is no way that you well be able generate more photons. Thus no gain and only the high probability of deteriorating overall beam quality.

5. Jun 23, 2004

### relativelyslow

if the first laser excited the lasing medium, would the resulting "second" laser be in sync?
the contraption im thinking of is not a closed beam of light. the first laser would shine into a one way mirror so that it goes in but cannot (at least mostly) escape back through it. then it excites the lasing medium in the second part. the newly combined laser would work the same way as in the first part (photons bounce back and forth in between the mirrors until they produce a coherent beam). set up like this would it work?

6. Jun 23, 2004

### Entropy

I'm just guessing here but I mabye you could reflect a beam of light in such a way that you "store" it in a mirror loop and over time add more and more light waves into the loop. Then once you have enough light in the loop you remove one of the mirrors and allow all the light to leave at once producing a denser ray of photons.

7. Jun 23, 2004

### chroot

Staff Emeritus
You can use one laser as a stimulus for another lasing medium, fine -- but you're not creating any energy by doing so. The energy given up by the second lasing medium comes from whatever pump mechanism is responsible for producing its population inversion, just like the energy from the first laser.

You can't beat the conservation of energy.

- Warren

8. Jun 23, 2004

### relativelyslow

ok. thanks. that makes sense (its good to have people who remember the laws, no matter how basic they are). so the laser cannot be the stimulus to the second laser; at least without losing its energy. what if the second laser was excited by an outside source (probably much like the first one). could the first laser mesh with the second one and strengthen?

9. Jun 23, 2004

### chroot

Staff Emeritus
As I said, one laser can certainly provide the stimulus for another. You can "amplify" a laser pulse this way -- but again, you're not getting something for nothing. Each amplifier stage uses more energy than it produces in light output.

- Warren

10. Jun 23, 2004

### relativelyslow

getting something from nothing wasn't my goal; sorry if i made that confusing. my objective was to find out if you could increase a lasers power, essentially, by adding more and more lasers to eachother

11. Jun 23, 2004

### chroot

Staff Emeritus
Yes, you can use lasers as optical amplifiers. That much should be apparent by the name LASER itself: Light Amplification by Stimulated Emission of Radiation.

- Warren

12. Jun 23, 2004

### relativelyslow

yeah i guess. so when the lasers are mixed, they should mix constructively (not destructively)?

13. Jun 23, 2004

### chroot

Staff Emeritus
Well, if you shine coherent light into a lasing medium, you're guaranteed that the stimulated emission will have the same phase and also be coherent.

- Warren

14. Jun 23, 2004

### relativelyslow

ok. well thanks for clearing up what should have already been clear. i think im going to have to try this. ive been interested in building a laser from "scratch". "scratch" because ill use already made tubes. if you did this enough with an HeNe laser, would it be able to cut throught things (at least set fire to paper)?

15. Jun 23, 2004

### chroot

Staff Emeritus
It depends on the kind of lasers you have. You can't just daisy-chain ten 1 mW lasers and hope to get more than 1 mW out of the final laser. Last but not least, please be very careful -- lasers with enough power to burn things are not exactly the sort of things you should be playing with at your level of understanding. I recommend you get some training first.

- Warren

16. Jun 25, 2004

### relativelyslow

i know. ive been reading this website called sams laser FAQ. it has pretty much everything you need to know about lasers. i wouldn't set out to burn things with it right away. id need a working one first. it would just be cool. do they have radio lasers? that would be really cool for some reason...even though you can't see the beam (visually).

about the daisy chaining, i thought that whole stuff about amplification said i could make it more powerful

17. Jun 25, 2004

### Integral

Staff Emeritus
If, as you first mentioned, you simply reflect a beam back into itself there is NO guarantee that you will be in phase with the beam in the laser tube.

As I tried to say before, there is fixed number of photons available for lasing in ANY laser, if you are already operating near that maximum limit further stimulation will NOT help. The way to get more power out is to increase the number of electrons in the inverted population. What you want to do is find a way to pump more electrons into the excited state, then you will increase the power out. Of course laser tubes are designed to run at some maximum power, if you find a way to push them beyond that limit you may find that the optics will fail, since they can be power sensitive. Any mirror adsorbs a small percentage of the incident beam, if you increase beam power you increase the temperature of the mirror, failure can result.
Then your project will be to build a power supply, not a laser!

18. Jun 27, 2004

### relativelyslow

im assuming lasers need a power supply. im just saying what sams laser faq is suggesting. its probably telling me how to build both.