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What lasers are used in lasik?

brendon7358

brendon7358

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I have a school project for ap chemistry and we need to disprove a movie scene, I am using this scene
I need to know what the max power of the lasers used is to prove that it cannot do that kind of damage, so far I have been able to find out that they are 193nm (not red!) and the gas laser is called an excimer laser, but I need more information. If you guys could help me out that would be great. If you could include sources that would be even better. Thanks :D
 
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Excuse the crudity of my research but I got some information for you.

Seems like the laser ussed is an ArF laser (uses argon and fluorine). It's lases at 193nm and has a relative output power of 60mW.

But while doing research on lasik it shows, as I thought, that the laser output is being pulsed. Seems to be about the 1mJ range for a 10 - 20 nS burst.

This translates to 0.00000001 mW per burst.

If used in CW mode (which is impossible) this translates to 1 x 10^9 mW.... which is more than enough to cut through 5 inches of steel like butter, plus anything else behind it.

If I was to make a guess, I would say that there is most probably about a 1mS delay in pulse output. Which would make the total system capable of 0.00001 mW. So in short the movie scene is BS. As well as the fact that water on the powerpoint (in another room) affects the laser system enough to increase the power of the laser. Maybe add in your report that, the laser has electronics that cleans the incoming power via a UPS and other means, and if a fault if found the laser will not fire until power is restored or the patients eye is correctly aligned with the laser source.

-Adrian
 
bobhaha said:
Seems to be about the 1mJ range for a 10 - 20 nS burst.

This translates to 0.00000001 mW per burst.
Click to expand...

zZfF9Sh.gif


You've mixed up your fractions or something because you're off by THIRTEEN ORDERS OF MAGNITUDE. If I were to say the US population was seventeen... or even if I said the universe has existed for two minutes I would be closer to being correct than your statement here.

Seriously... Does this answer even make sense to you? You know lasik works by vaporizing corneal tissue. In your experience, is 0.00000001 mW capable of vaporizing tissue?

bobhaha said:
If used in CW mode (which is impossible) this translates to 1 x 10^9 mW
Click to expand...

7pgy3Qc.gif


What in Rod's name are you talking about? Who is doing your "translating"? Are you just making shit up now? Show your work please.

bobhaha said:
If I was to make a guess...
Click to expand...

Well that settles it. Guessing is "making shit up" in my book.

bobhaha said:
I would say that there is most probably about a 1mS delay in pulse output. Which would make the total system capable of 0.00001 mW.
Click to expand...

Is this an extension of your first calculation failure, or is this something new?

bobhaha said:
Excuse the crudity of my research
Click to expand...

NqTZOB0.jpg
 
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It's right in the sentence, sir. Millijoule. Energy. Power is energy per unit time. If I have a 1mW laser on for one second, the total energy emitted is 1mJ. If I have a 1mW laser on for one minute, the total energy emitted is 60mJ. If I have a 100kW laser on for 10ns, the total energy emitted is 1mJ.

As an advanced placement chemistry student, you should know what energy and power are.
Even if you've fallen behind in your class, these answers are 4 seconds away with Google. You're not trying very hard here.
 
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Cyparagon said:
It's right in the sentence, sir. Millijoule. Energy. Power is energy per unit time. If I have a 1mW laser on for one second, the total energy emitted is 1mJ. If I have a 1mW laser on for one minute, the total energy emitted is 60mJ. If I have a 100kW laser on for 10ns, the total energy emitted is 1mJ.

As an advanced placement chemistry student, you should know what energy and power are.
Even if you've fallen behind in your class, these answers are 4 seconds away with Google. You're not trying very hard here.
Click to expand...

Yes, but we have to do an experiment to prove it would not work. Because I do not have an excimer laser I was just going to use a handheld laser, but I need to know what power it needs to be. That's why I needed it in mW not mJ, I understand that 1mJ = 1mW in a second but it's a pulsed laser, so I need to find a way to accurately simulate it with a constant on laser.

I will use this laser as an example, because it gives the following information:
Wavelength: 193nm
Pulse Duration: 8-30 nano seconds
Repetition Rate: 10hz
Fluence (at the eye): 134mJ

1 Nanosecond = 1.0 x 10^-9 Seconds
So to calculate mW per second, 30 nano seconds is 3 x 10^-8 seconds and it would be repeated 10 times in a second, according to my calculations this would be in the MW... Or it would be very small (.00004mW), I must be doing something wrong here.
 
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Lets not forget spot size. It's focused at the just past the corneal surface. This makes it a peak energy per unit area problem. In fact the Fluence (cough,, hint... cough) gets so high that it becomes a ablation, not a combustion, method of removing the tissue. So a low AVERAGE power works just fine for Lasik. In this case the pulse has a very high PEAK power, which is what can be misleading to a person new to the calculations. Besides, even if you drilled through the cornea, the deep UV energy gets partially adsorbed in the Aqueous Humor. The AH is 98 per cent water, and the novice chemist should easily be able to prove that it would take a long, long, time to boil that water. (hint two, its not just the water that adsorbs, its really the other 2%, but does it adsorb enough?) Change the wavelength to say 532 or 1064 nm where the mix is transmissive, and then... well, ouch. The audible shockwave of a plasma breakdown in the AH would be un-nerving to say the least.

Things to Google include Ablation and Latent Heat of Vaporization.... Aka Enthalpy of Vaporization....

If you understand Calculus, the basis of Lasik, per pulse, is the very high Delta Energy over the very short Delta Time.

At least you did not pick this scene:

Real Genius (8/8) Movie CLIP - Jerry's House of Popcorn (1985) HD - YouTube

Some things to look at:

Laser (peak) Fluence, Intensity and Power - LIDARIS

Sensor Finder | Laser Fluence calculator - Ophir

"Adsorption Curve"

I'd show your math and cite your sources.

If you get a bad grade and need to defend yourself, find the very common book:

Safety with Lasers and Other Optical Sources: A Comprehensive Handbook
by David Sliney, M.L. Wolbarsht

The math in S&W is very basic. It grows mold on the shelves of most University and some Public libraries. I've yet to meet a university library that would deny you access for a academic project. If you are unsure, your local University Laser Safety Officer might also take your call.


Steve (Former pulsed laser service engineer)
 
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