Lazors

What stops a lazor from going completely through an object . . . like say . . . an eyeball?

-Chrystal Pond

I have four answers for that question;

First answer;
Its Laser. Light Amplification by Stimulated Emission of Radiation and not Lazor as spelled by Chrystal and Strongbad. ( I told you that I would always find something in your question to make fun of, so thanks Chrystal for making it so easy!)

Second, in Lasik there are two ways of cutting the lasik flap; the Intralase method and the microkratome method.
The microkeratome method uses a surgical blade driven by a miniature geared motor to slice the epithelium. The flap is pulled aside and then the laser is activated.

The reason the lasik laser does not go completely though the eyball is by design, the material being removed, corneal tissue, is matched with the wavelength of the Excimer laser 193nm (or .000000193 meters).

The corneal tissue absorbs completely the 193nm wavelength, when the energy of the laser pulse is absorbed into the corneal tissue molecules, it breaks the bonds and the result is a solid to plasma to gas transition. Isn't that freakin awesome!??! Your eye tissue turns to a plasma for a microsecond!

This phenomenon is called surface ablation. Only the very top surface of the corneal tissue is affected by the laser, this is the whole scientific principal for why lasik works. By ablating only certain amounts and parts on the corneal surface we can reshape it to give you perfect vision, cool eh?

Alright, third answer;
The intralase method is so crazy cool. Instead of using a blade (how 1800's!) the intralase laser (IL) uses a completely diefrent scientific principal. It uses a specific focal point at precise depths to create a tightly packed layer of bubbles under the epithelium, that can then be lifted to allow the excimer to ablate the cornea.

A good example of the way the IL works are these;
They are 3 dimensional pictures inside of a glass cube, you've probably see one at the mall.

They work by moving the focal point of a pulsed laser (one pulse per bubble) to the programmed points of the image being created.









When the beam enters the top layer of the epithelium, it passes though without harm until it comes to the focal point of the beam. At that specific point, all the IL beams energy is concentrated in a spot the size of the tip (not the head) of a needle. It heats the spot for a femtosecond (.000000000000001 second). This creates a small bubble because the gas created by the pulse has to go somewhere.

Any remaining IL light is harmless because its lost its power once it passes the focal point.



And finally;
The majority of high power lasers will bore a hole straight though your skull if you're crazy enough to get one at eye level.
Oddly enough, there has never been a reported death caused by a laser beam. Now this doesn't mean that people haven't died working on the 50,000,000 volt power supplies or because the beam ignited a gas canister, but the beam itself had never killed anyone.
But it could.