What is a laser?
We have extracted the definition of the NTP 261 of the INSHT, since it defines it of precise form and briefly. According to the technical prevention note 261 a laser is defined of the following form:
“The láseres are devices that produce and amplify a bundle of electromagnetic radiation in the interval of wavelengths of 200 nanómetros to 1 millimeter, like result of a controlled stimulated emission. The obtained bundle of radiation of this form has three properties that separate it from the obtained radiation of conventional sources. It is monochrome (of a concrete wavelength), it is coherent (all the electromagnetic waves coincide with phase) and it is expressed in a certain direction (with very small angular difference, so that the dispersion of the bundle is not significant with regard to his length)."
The characteristics of a laser as the following ones are the NTP 261: wavelength of emission, duration of the emission, potency or energy of the bundle, diameter of the bundle and difference.
So that you should do better an idea, we are going to be explaining the principal characteristics of the laser, but earlier we are going to try to understand how a laser works.
A laser (initials in English of “amplification of the light by means of stimulated radiation emission”) consists of different parts that possess different properties and functions. To start we need what is known as an active way (1). It is a question of the chemical compound that is inside the device and that we will excite so that it expresses the light laser. To produce the excitement there is necessary an energy source (2), which is usually a battery, to produce the energy pumping. Once exitados the atoms, the external electrons droop and they begin expressing the first photons. And here there begins real stimulated emission that names the laser. The walls of the active way are two reflecting mirrors. One of them is reflecting to 100 % (3) while other (4) presents a small transparence. The photons bounce infinity of times between the mirrors and in every step along the active way, if they collide with an excited electron this one droops and expresses another photon. This process realized constantly produces a big number of photons with the properties of coherence and without phase lag, which we will explain further on. And after all this almost instantaneous process there is generated the bundle of the laser (5) that goes out for a small gap in the mirror (4).
The wavelength has no loss. His color talks each other of the wavelength of the light that expresses the laser, that is to say. They are, between slightly secondhand others, in red color (630 nm), in green (532 nm), in violet (405 nm) and even in infrared that is not visible for the human eye (808 nm). Generally every laser works with a certain color (it is monochrome) that depends on the chemical compound that is in his interior and that produces the bundle.
Different types of laser exist as the way of expressing that they have. By agreement the time of extreme emission is chosen between a laser of continuous emission and one of emission touched in 0,25 seconds. If the pulse of light that expresses the laser is expressed in more than 0,25 seconds it is considered to be a continuous laser, while it does it in less time he is considered to be touched. For the user scarcely there is difference, but in practice yes that it is. For example, the touched láseres are useful in the materials ablation when you want vaporizar a small material portion. With a short but intense pulse you might do it, while with a continuous laser the energy would vanish for the rest of the material without achieving the looked vaporization.
The potency or energy of the bundle indicates us the grade of power that has the laser. Major how much is the potency, as well as the energy, more dangerous will be the laser, since more power will have to "burn" the materials in which it affects. For example, the top laser that the speakers use in a conference generally does not overcome 5 mW, what makes them quite sure, but a laser for astronomical observation of 100 mW expresses with more power and it is capable of causing serious damages. Further down we will see a video of a laser of 125 mW in action. For the continuous láseres it usually give the potency in watts, but for the touched láseres another form exists. It is a question of Julys divided per time. For example, if we say that a laser is 150 mJ/10 ns it means that the laser expresses 150 milijulios in pulses of 10 nanoseconds.
The characteristic most emphasized from the láseres is few dispersion that he suffers. Any bulb expresses a light in all the directions of the space, while a laser expresses a bundle in the only direction. This owes to the coherence of the light that it generates and to that is cofiled perfectly. The coherence is only a property of the waves for which these support a difference of constant phase, what in our case comes to say that all the expressed photons have the same phase. This, together with the colimación, which consists of doing that all the photons have the same direction (they point towards the infinite), it does that they do not interfere between themselves and that the bundle is supported during more distance without dispersing. For example, the bundle of a laser normalito of He-Ne pointing at the Moon only expands 1,6 km (diverges) in 384.000 km that it covers.
A property that arises from that the bundle of the laser diverges little and of his potency is that it can go so far as to burn the materials in which it affects. This is due to the fact that the area that receives the impact warms up like result of the continuous reception of photons focused in a very small area. It is similar to when we take a magnifying glass and focus on the beams of the Sun in a small point. The material on which we focus (an ant if we are bad persons:P) can go so far as to be burned by the sufficient exhibition time. The láseres of 100 mW are already sufficiently powerful as to be able to burn small things as role or make to exploit balloons (pointing at some area of black color). The most powerful láseres of several W are already used to cut wood and those of even major potency to cut metal.
We leave you with a video in which it is possible to see what a laser of 125 mW can do.
Are they dangerous the laser that is used in public places as in discotheques?
The technical note in prevention 261 says this way: "the aptitude of a laser to produce a risk will be determined principally by the first three factors: wavelength, duration or time of exhibition and potency or energy of the bundle.”
As we were mentioning that more above with láseres of 100 mW we can already burn things. In different experiments there have put themselves to the test different types of laser and his aptitude to cause observable damages in the animals retina. Let's remember that the part of the human body that more risk has opposite to the possible damages of a laser is the retina. For example, with a laser of 74 mW it is possible to hurt with a time of exhibition of 2 milliseconds in a Monkey Rhesus, while 20 ms was needed with a laser of 36 mW of potency. A Krypton laser with a wavelength of 586,2 nanómetros and a potency of 22,5 mW produces damage with a time of 33 ms exhibition and with 25 mW if it is exhibited during 16 ms. Even with a laser of 10 mW damage takes place with a time of exhibition of a second.
Now we go to the articles laser known. So that we do an idea, a top laser to ourselves to indicate things in a conference, it can have in most cases between less than 1 mW and 5 mW (as we have commented previously). Even with a potency of 5 mW they can go so far as to hurt with a long exhibition time. In adults it is supposed that the same act of separating the look is a sufficient protection, but in children clinical cases have happened with reversible injuries for a long exhibition (approximately 10 seconds, producing edema to him to blacken). An exhibition prolonged with this type of láseres might produce of course permanent damages also.
But: How much potency do the láseres of the discotheques have?
There are very varied ones, but to do an idea to us, they are for example of 10 mW, of 30mW, of 40 mW, of 80 mW, even of 350 mW. You can imagine what this type of láseres can do to him to our sight: no?
To simplify a little the things, the láseres as they gather together his danger grade in different categories, as 654 turns out to be reflected in the technical prevention note. This way we have left the following categories: type 1, 1M, 2, 2M, 3R, 3B and 4.
We have found papers that he accompanies to some of these devices like cards and instructions. After reading the indications that appear in some of the devices that are used to generate animations laser in discotheques, we could have verified that the majority they turn out to be catalogued in the proper instructions of the device like laser of type 3B (although they are also of type 3R or 4 for example). To know what that means we can come to the technical note in prevention 654, where the following thing appears in the type 3B … ”The direct vision of the bundle is always dangerous, while the diffuse reflection is normally sure”. In fact in the same instructions of some devices it is warned in the shape of text that the lightest direct radiation is dangerous for the sight and can cause permanent damages in the retina.
An interesting study must exist round there precisely on láseres of discotheques. They quote it in different places as in the BBC and in consumer. We can extract some parts, although more interesting it is to bring in and to read these pages. For example, on the page of the BBC (here in Castilian) we can read …
“Lasers used in nightclubs could damage dancers' sight, researchers have warned.”
And of that of Consumer …
“The popular lights laser that are used in the discotheques or night clubs of half a world can affect to the vision of the persons who frequent this type of places, according to a report of the Meeting of Radiological Protection of England (NRPB in his initials in English) quoted by the BBC.”
We can see more information about the topic here...
But: how they put these láseres in public places!? Moreover: how they allow that to be made!?
An important point is that the láseres do not produce damages if they are used correctly. One of the principal problems can come for his undue use. The manufacturers have obligation to accompany the device of a few instructions of use between other things. Here we can read on the topic.
Reading the manuals of some of these devices, in them it is said clearly that the laser bundle must not settle in such a way that it gives straight to the eyes of the persons (in addition to other specifications, like which there must exist the figure of an expert in control of laser … etc …).
If a slightly powerful laser will be used or the installed system one had such form that the radiation laser that was coming to the public was not overcoming the established limits, from the point of view of the risk it would be correct. But what is clear is that what it is not necessary to do is to use a powerful laser and to direct it straight on the persons.
If the businessman does not use of suitable form this type of technology, it can achieve that the sight of the user finishes damaged. Frequently it might happen that or the businessman uses badly the device or sometimes even it does not even receive the information adapted about his functioning.
In some cases if the laser is the sufficiently powerful thing, it is possible to go so far as to produce a real disaster. Do you remember what happened in Russia in a concert? Since that itself. It began raining and the "technical staff" thought that he had not greatly sense to point with the láseres at the sky as they were reckoning, since they had covered the dance floor and this way “the beams” were not going to be seen. So they aimed at them straight towards the dance floor. The láseres must perform high potency, I suppose that of class 4, for the effect that took place in the sight of the assistants of so sharp form. The news as pais.com …
“Tens young people who took part last July 5 in a music festival dance outdoors close to Moscow they have lost part of the vision after the laser used during the spectacle was burning his retinas, have admitted Russian sanitary sources, that they have confirmed 12 cases.”
“"Partly this has owed to the rain, but also to the ignorance of the technical staff, by force of the used, extremely powerful laser for a small space as the place in which the concert was celebrated", has shown Valentin Vasiliev, owner of a company of rent of cannons of laser.
Meanwhile, the promoters of the festival of electronic music keep silence, while the local authorities affirm that they never went so far as to receive an authorization request to celebrate the event, according to the digital newspaper Gazeta. Ru.”
“"What you saw there were annoying spots, like when you look at the sun", he has said to Kommersant Dmitry. "After three days, I went to the hospital. The doctors examined me and asked me if it had been in the festival. I agreed, and they deposited me straight; I could not to house take my things again", he has reported.”
The ocular damage
We were saying that the part of the eye that covers more danger is the retina and that the produced damage depends straight on the energy of the bundle laser. But, what more factors influence the appearance of the burn?. On the other hand, although the retina is the textile that has more possibilities of be damaging: cannot other ocular structures fall ill with the laser?
The key is in another parameter that we have mentioned at first: the wavelength. We were saying that for the proper nature of the laser, they are monochrome or almost monochrome. Namely they have only one wavelength, only one color. In the visible bogey of the electromagnetic radiation, the optical structures of the eye (cornea, watery, crystalline, glassy humor) are transparent. Namely the light does not intergesticulate with them. With the laser the same happens: if the laser is visible (that is to say, his wavelength will be minor than the infrared ones and more than the ultraviolet ones) it will cross the cornea, the crystalline one and the humors of the eye without affecting them, although the energy of the bundle is high. For example, a blue, green, red or yellow laser of 500 mW, that with this energy is very dangerous for the eye, will not burn the cornea or the crystalline one. Of general form, it is accepted that to energy equality, the laser that more damage produces in the retina is that 550 is next to nanómetros (green color). But we understand that any visible laser (and infrared of of short wavelength) they can affect to the retina.
On the outside of the visible bogey, the things change. In the infrared near one to the visible light, there are still supported the optical properties of the visible light: the optical structures keep on being transparent, and the infrared radiation still comes to the retina. In fact, there are medical tests that use infrared radiation to study the retina: the angiografía with green indocianida, and the scanner of optical coherence (the last one uses in fact an infrared laser). For the infrared radiations of major wavelength (in the bogey, more removed from the visible light) the optical means are already not transparent. And with the ultraviolet light the same happens, the eye is opaque and the radiation does not come to the retina, stays in the cornea.
These characteristics take advantage in ophthalmology: if we want to use a laser with an effect in the cornea, as it happens with the surgery of the myopia, the ultraviolet bogey is used.
Therefore, already we take the principal reason as that the habitual láseres (that are in the visible bogey) affect to the retina. Also an interesting effect takes place: the transparent means of the eye are in charge of focusing and concentrating the light beams on the retina, from this form the projected image originates. If we point with a laser at the eye the same happens: the lenses of the eye concentrate the energy of the laser on a minor area of the retina, therefore there takes place major damage (more energy in minor surface, major thermal and photochemical effect).
Well, already we have a bundle laser of the visible bogey that crosses the transparent textiles of the eye and comes to the retina. What happens then?. Most of the textile retiniano is transparent, and the laser crosses it up to the most external part: the epithelium pigmentario and the fotorreceptores. This area has pigments that prevent the transparence. The photons then interact with the textile. A principally thermal damage takes place (although to very high energies a photochemical damage takes place), the temperature increases suddenly several grades, too rapidly so that the mechanisms of thermal dispersion act. The heat propagates to other more internal layers of the retina, and to adjacent retina areas.
Factors that are going to determine the visual damage
Most of the burns retinianas for the laser does not cause a valuable visual loss. Namely it affects in little or not at all the visual function. This the ophthalmologists know it very well, because for a series of illnesses of the retina (principally as regards the diabetes), sometimes they have to produce small burns for almost the whole retina, and the patient does not notice any visual loss. This is like that because the thin vision, which allows us to visualize the detail, corresponds to a small surface of the retina, the most central, which it is named fóvea. The impacts laser (both accidental and therapeutic) far from the fóvea are not going to produce visual problems: the peripheral retina corresponds to the peripheral visual field, which has spatial resolution small, and a loss of sensibility produced by a burn is not translated in effects biologically excellent. [I always speak of láseres with energies of the parameters that we have indicated more above, how maximum of a few hundreds of milivatios. Some industrial láseres of major energies yes can produce major damages in peripheral retina, like hemorrhages or perforations retinianas].
If the light impact affects in the fóvea, the things change: any permanent damage is translated in an irreversible visual loss. The retina here is thinner (less dispersion of the heat, more damage in the textile), the epithelium pigmentario is darker (more light absorption, more damage) and the fotorreceptores are much more nearby between themselves (major number of fotorreceptores damaged by surface unit, less spread between them to remove the heat).
A light is projected straight in the fóvea when we look straight at this light. Therefore, the most dangerous thing when a device laser points at the eye, it is to look at it straight. It is a reflex: if something pays our attention in our peripheral visual field, we focus it straight ahead, and if it is a light laser exhibit our fóvea.
But not all sound disadvantages. The same as we have the reflex of looking straight ahead at a light, also we have other of us to separate when this one dazzles us.
The láseres that are used in the discotheques work in the visible bogey. When the fóvea turns out to be dazzled, we have a protection reflex that separates the eye, it closes the eyelid and even can turn the head. So used laser depends on the system the direct exhibition might hurt.
For speaking with the numbers in the hand, an answer of habitual dazzle limits the exhibition of the fóvea between 0,15 and 0,25 seconds. For a top laser, which has few potency milivatios, it is more than sufficient. The leader would be risked to leave for example in hands of a small child, that playing yes that his fóvea might exhibit during several seconds. A leader of 5 mW would need an exhibition foveal concerning 10-20 seconds.
For the láseres of the discotheques mostly of class 3B, a reflex of normal dazzle might go so far as to hurt (let's remember that experimentally with a time of exhibition of 16 milliseconds damage takes place with a laser of 25 mW of potency and is not so rare to find devices of more than 30 mW in the rooms and holiday). A more simple-minded answer (let's think about the relative visual disorientation for the lighting conditions, if the subject has taken alcohol, etc) can be translated in a burn of the fóvea.
Other less important factors exist. The diameter of the pupil influences, so that when the pupil is wide (as for example in the discotheques or any slightly illuminated environment) the damage will be major. Those of darker race have more possibilities of turning out to be damaged, because the epithelium pigmentado of the retina, as the skin, will be more pigmentado and will absorb more radiation. And the graduation defects (like the myopia or the farsightedness) act like protectors whenever one does not take glasses or contact lenses: it implies that the laser does not focus well in the retina.
And the injuries, why are no many any more people with ocular injuries due to the láseres of discotheque?
There are several motives for which finally the injuries might not go so far as to take place or might not go so far as to be notified. One of them is that in the experiments in laboratory and the industrial accidents, the distances are 1 or 2 meters, while in the discotheques most of the people might be at major distance. Another reason might be that most of the people do not look straight to the bundle at laser, as we mention above, or that the fact of separating the look in some cases could be sufficient. Or the injury might go so far as to take place but for ignorance not to relate it to the exhibition to laser. This document is interesting with these and some other notes on this point. Anyway everything depends on the potency of the laser, of how it is installed, the exhibition time... the commented previously we go. And it is clear that with the suitable laser and the opportune conditions the injuries might go so far as to take place, as it happened already in the concert of the disaster.
In short: to look at a laser straight straight ahead during a long time, in a slightly illuminated environment, there will be the most dangerous conditions. And we know that the láseres used in discotheques can use energies that we already consider to be dangerous if they aim at the people instead of to the walls or the roof. Therefore, when less avoid to look straight at the bundle laser, and if it happens, separate quickly the look.
Written by Wis, Ocularis and Héctor.
Sources
Wikipedia
NTP 261
NTP 654
BBC
BBC (in Spanish)
The Country
Consumer
Lukor
Consumption
Source image
Laser eye insult. Barkana Y, Belkin M.
Surv Ophthalmol. 2000 May - June; 44 (6):459-78. Review.
PMID: 10906379 [PubMed - indexed for MEDLINE]
Microorganisms: that do not take the sandwich from you!
What hides the series "Heroes"? Streaming Desperate Housewives S06E17 Chromolume #7 now
No comments:
Post a Comment