1. The electromagnetic radiation hazard of laser
Take Helium-neon laser as an example. Discharge and collision make the free electrons, helium atoms and neon atoms gain energy, so they all become the source of electromagnetic radiation, part of which can be amplified laser radiation, output Later it becomes laser; the rest is called Collateral radiation.
1. The danger of laser
The high intensity of laser light makes it interact with biological tissues extremely violently photochemical (Photochemical), photothermal (Photothermal), photodynamic (Photodynamic), photodisruption (photodisruption), light wave electromagnetic field, etc., causing serious injury. The surrounding equipment, especially combustible and explosive materials, can also cause disasters. Interference caused by a high degree of coherence makes the light at constructive interference stronger, thus causing higher harm.
a. Danger to the eyes
The cornea (Cornea) and conjunctiva (Conjunctiva) of the human eye are not protected by the cuticle of the general skin, and are most vulnerable to light beams and other environmental factors. The intensity of the laser light is so high that the injury caused by the reflex action of the eyelid has a protective effect.
The damage to the eyes is related to the wavelength: IR-A in Visible light and Infrared affects the retina; UV-B, UV-C in Ultraviolet and IR-B, IR-C in Infrared Affect the cornea); visible light and short infrared (Near infrared; IR-A) will pass through the clear eye material and be absorbed by the retina, so if the beam is too strong, it will damage the retina. The high collimation of the laser light allows the light to converge to a small spot, about 10 to 20 μm on the retina (thinner than the hair). Therefore, laser light between 400nm and 1400nm has a particularly high risk to the retina. This band is called the retinal hazard region (Retinal hazard region).
Due to the effects of heat flow and shock waves, the tissue surrounding the imaging area may also be damaged, with more serious consequences for visual function. Because the repair ability of retinal nerve tissue is very low, this injury is generally permanent.
Electromagnetic waves outside the danger zone of the retina, including ultraviolet rays and long-wave infrared rays, may injure the front part of the eye. Some bands can damage water crystals, and the radiation from 295nm to 320nm and 1μm to 2μm is particularly serious. Ultra-wide band ultraviolet rays and infrared rays with a wavelength greater than 1400nm may damage the cornea. When only the corneal epidermis is injured, it can be repaired within a day or two, and the vision is completely restored. If there is significant damage to the deeper parts of the cornea, Corneal scars can result and permanent blindness can result.
In terms of tissue penetration depth of infrared rays, 1,440 nm (such as some semiconductor lasers), 1,540 nm (such as erbium-glass lasers), and 2,100 nm (such as holmium-Jacques lasers) are all greater than 10,600 nm (carbon dioxide lasers), so the first three The risk of permanent injury is relatively high . The 308 nm xenon chloride (XeCl) laser beam will immediately cause cataracts in water crystals, so it also has additional dangers. Lasers such as argon ions (, krypton ions, KTP frequency doubling, copper steam, gold steam, helium-neon, neodymium-yak (Nd: YAG), etc., are potentially dangerous to the retina. Er: YAG, erbium- Lasers such as lithium yttrium fluoride (Er: YLF), holmium-Jacques (Ho: YAG), hydrogen fluoride (HF), carbon dioxide (CO2), carbon monoxide (CO) are dangerous to the cornea
b. Danger to the skin
The cause of skin damage may be photochemical reactions (mainly in the ultraviolet band) or thermal effects (mainly in the infrared region). For example, erythema (sunburn) is caused by epidermal injury, and sometimes the dermis also has a certain degree of damage, and these injuries result from reactions caused by photochemistry. If you understand the dangers, the skin protection measures required for the excimer's ultraviolet lasers are easy to plan and implement. Visible light and infrared laser beams may cause first-, second-, and third-level burns. Irradiance that can cause severe thermal burns can also ignite textiles and burn plastics. The severity of the injury depends on the length of the exposure time and the penetration depth of the laser light. Generally speaking, if the exposure time lasts for 1 second or longer, the pain reaction will cause evasive action, leaving the illuminated part away from the beam, so the exposure time will be only 1 second or less. If the irradiation time is very short, a high-power laser beam of 10.6 μm will not cause deep tissue burns, because the penetration depth of this wavelength is very shallow (about 20 μm), and in fact will not penetrate the thickness of the normal cuticle. The damage of the carbon dioxide laser to the epidermis is due to the heat conduction from the stratum corneum to deeper. However, when irradiated with 1064nm neodymium-Jacques short pulse wave, because it can penetrate a few mm and enter the tissue, the exposure just above the burn threshold is enough to cause deep and serious burns. Holmium-laser (2.1μm), KTP frequency-doubled laser (double-frequency neodymium-Jacques, 532nm) or argon laser (488 and 514.5nm), the burn depth is between CO2 and neodymium-Jacques. The laser spot, or the dense irradiance at the tip of the fiber, is used to vaporize or peel the tissue, so it is very dangerous for the skin near the focus. The reflected laser beam may ignite clothing, causing skin damage and tragic consequences. The actual threshold for skin injury is usually several J / cm2 spectra, and this level of exposure does not occur outside the focus of the surgical laser.