What Actually Damages Your Eye?

Hello,
Okay so I just have a general question with lasers and how they damage your eye.

If you were to actually get the beam/dot into your eye, what is it that causes damage?

I searched the forums and couldn't find anything, so I thought I would make a thread.

Thanks very much!

well if you look on line you will find allot on this, its important to be aware we don't have all that great of data, as who is going to stare at a powerful laser to test the data. IR EM energy is a heat beam and can burn some clear things like you lens and cornea, green burns dark objects like cones rods and blood vessels in your retina, blue and UV and cause some of the same problems as green but can also cause a chemical reaction in bio matter, my rule of thumb is the more power in MW and the lower the wavelength the more issues you run into. To be honest its a crap shoot though, but you get hit with an energetic beam of coherent light in you pupil its gonna suck as you will focus it down to a pinprick of intense energy. IF you look up MPE standards you can see the ratings they list, if you times the limit by 10 you get 50% chance for permant damage.

also scope this out http://laserpointerforums.com/f53/hit-eye-1000mw-445nm-blue-laser-69469.html

thermal damage mostlym from non-ionized laser radiation.

a better description of the issue near UV eg.. 445nm 405nm "Near ultraviolet radiation, although technically non-ionizing, may still excite and cause photochemical reactions in some molecules. This happens because at ultraviolet photon energies, molecules may become electronically-excited or promoted to free-radical form, even without ionization taking place." as taken from wiki on ionizing radiation.

Thankyou both for your answers. I'm now going to go on Wikipedia!

The damage is not caused by overloading your eye with light, it's caused by said light producing intense heat within the eye. You can do all kinds of nasty things like rupture blood vessels.

absorbed energy is heat whats the diff? Too much of any energy from EM radiation dependent on the band gap of your eye and the power as expressed in wavelength that can move your electrons to a higher energy and this causes heat. Or am I mistaken Not trying to be a butt, but I want to make sure I am on the same page. The reason more power makes more heat is our power in W is just how many photons per second leave the laser? More photons means more photons absorbed= more electrons in a higher energy state= more heat.

I am at a loss describing how the laser would heat up a liquid though, as I am not sure how band gaps work in anything but a solid. Even then I am no where near an expert.

TheReddish said:

absorbed energy is heat whats the diff?

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Absorbed energy is not always converted to heat. If this were the case, solar panels would be 0% efficient. Energy takes many forms.

TheReddish said:

Too much of any energy from EM radiation dependent on the band gap of your eye...

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Individual molecules have band gaps, not objects such as the eye.

TheReddish said:

...the power as expressed in wavelength...

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Power is not expressed in wavelength.

TheReddish said:

your electrons to a higher energy and this causes heat.

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Heat and changing energy levels aren't the same thing.

TheReddish said:

power in W is just how many photons per second leave the laser?

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The number of photons times the energy of each photon. Photons of higher frequency (or lower wavelength) have more energy.

Cyparagon said:

Only if it is ionizing radiation. The lasers we work with are not ionizing.

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Actually, ionizing radiation creates ions, which is when the electron is given so much energy that it is ejected from the atom entirely. Simply moving up and down between energy levels is exactly what electrons do when stuck by non-ionizing photons. When they drop from high to low they emit other energies in the form of vibrations and IR and stuff. That's what heat is.

Sorry your corrections need some amendments:

Cyparagon said:

Absorbed energy is not always converted to heat. If this were the case, solar panels would be 0% efficient. Energy takes many forms.

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Depends on the wavelength of the EM radiation and the material absorbing it...In the case of solar panels the EM in the VIS region greater than around 0.5 eV causes an excitation of electrons across the band gap.

Cyparagon said:

Individual atoms have band gaps, not objects such as the eye.

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Atoms have orbitals (probability density functions) at different energy levels and molecules have molecular orbitals. Semiconductors are generally referred to as having Bandgaps.

Cyparagon said:

Power is not expressed in wavelength.

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There is a relation to energy E=hc/(lambda) and lambda is wavelength. As E is expressed in Joules and power is joules per second , there is a direct relationship between Power and wavelength.

Cyparagon said:

Only if it is ionizing radiation. The lasers we work with are not ionizing.

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Not true EM radiation at lower energies ie Visible light can and does excite electrons to higher energies. Ionising radiation has higher energies and can remove electrons from eg atoms and molecules and create ionised or charged particles.

Cyparagon said:

Heat an ionization aren't the same thing.

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Not in the context of the comment made. Exciting electrons does not require ionising radiation. Vibrational relaxation of the electron either to the lowest vibrational level in the first electronically excited state or the ground electronic and vibrational state does in fact liberate heat energy.

Cyparagon said:

The number of photons times the energy of each photon. Photons of higher frequency (or lower wavelength) have more energy.

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Ok photons per sec and their energy as given in formula above.

lol what started as a simple question seems to have not so simple answer, I have been enlightened by the discussion though and I bet he got more info than he needed from this :beer:

Thanks, I've made corrections.

grainde said:

there is a direct relationship between Power and wavelength.

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No, there is a relationship between a single photon's energy and it's wavelength. Power is not the same as energy, and the power of a laser beam has nothing to do with the energy of a single photon contained in it.

Ah well, it can get a bit confusing at times...

Power = energy per photon * number of photons per second

So a 1 mW red laser will emit a larger number of photons per second compared to a green 1 mW laser, and each photon emitted by the latter has more energy.

Compare it to loading a truck with pebbles vs boulders at a tonne per second: if you count the individual pebbles you will find a larger number, but the truck fills up at the same rate.

Be sure to read Xoul's account of getting hit square in the eye with a 445nm laser. I've never seen direct evidence of what a laser like that can do as those images he provided.

Cyparagon said:

No, there is a relationship between a single photon's energy and it's wavelength. Power is not the same as energy, and the power of a laser beam has nothing to do with the energy of a single photon contained in it.

Quote:
Originally Posted by grainde View Post
there is a direct relationship between Power and wavelength.

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Go back and read exactly what I said.... I agree, I never said that power = energy, but that there was a relationship between power and energy and yes, as I stated in the last comment the power of a photon is related to its wavelength too. Benm Summed it up nicely. :beer:

Cyparagon said:

The number of photons times the energy of each photon. Photons of higher frequency (or lower wavelength) have more energy.

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You omitted the per second bit in your comment.:yh:

Anyway a bit off topic now.....

I have a hankering to get me some pig eyes and do some testing to get some better results with what a laser could do to an eye ball. could be for an interesting test, I need to get a good macro camera first though. Unless someone else is equipped for this, and would like to do the experiment themselves, its hard to see what would happen, as few cases are well documented and not many folks are willing to go blind to test it. We can talk about it, but like the pick of Xoul's eyeball, a picture is worth a thousand words.