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Laser Safety Standards and Choice of Laser Safety Goggles

Laser Safety Standards and Choice of Laser Safety Goggles

Laser safety standards include American standard ANSI 136.1 and European standard EN207/EN208/EC60825.

1. American laser safety standard ANSI 136.1

Lasers are classified into the following categories according to the ANSI Z136.1 standard.

Class Definition Requirements 1 Non-hazardous without goggles 1M eye-safe visible wavelength laser (400-700nm), no magnifying glass when used Optical system without goggles unless with magnifying glass optical system 2 Eye-safe visible wavelength laser (400-700nm), (blink reflex Can prevent damage within 0.25 seconds) No need for goggles 2M eye-safe visible wavelength laser (400-700nm), (blink reflection can prevent damage within 0.25 seconds), no magnifying glass when using optical system It is recommended to use goggles 3R indirect observation beam may not be safe . The maximum allowable exposure (MPE) is up to 5 times for visible light class 2 lasers, and up to 5 times for invisible light class 1 lasers. It is harmful to the eyes. It is recommended to use goggles. 3B indirect observation of the beam is harmful to the eyes. Goggles 4 Direct and diffuse exposures are harmful to eyes and skin. There is a burn and burn hazard requiring eye protection and other personal safety precautions.

Class 1 laser, safe under all normal conditions of use. Means that the maximum allowable exposure (MPE) will not be exceeded when viewing the laser with the naked eye or with typical magnifying optics (telescope or microscope). To validate the standard, the standard specifies the aperture and distance relative to the naked eye, using a typical telescope to observe a collimated beam and a typical microscope to observe a diverging beam. It is important to realize that some specific lasers are classified as Class 1, but damage may still occur when using telescopes or microscopes with very large apertures. For example, a high power laser, with a very large collimated beam or a highly diverging beam, passing through the aperture with a power lower than the radiation limit (APL) of a Class 1 laser by standard definition, might be classified as a Class 1 laser, but when using Large-diameter magnifiers can gather unsafe power values.

Class 1M lasers are safe to use under all conditions except through magnifying optics such as microscopes and telescopes. Class 1M lasers produce large diameter or diverging beams. Class 1M lasers, which typically do not exceed MPE unless focusing or imaging optics are used to compress the beam. If the beam is refocused, the danger of a Class 1M laser will rise and the laser class will change. If the power passing through the pupil of the naked eye is lower than the radiation limit (APL) of a Class 1 laser, the laser can be classified as Class 1M, however, the use of typical magnifying optics will collect power into the eye that exceeds the AEL of a Class 1 laser and is less than Grade 3B AEL.

Class 2 lasers, are safe because the blink reflex limits exposure to no more than 0.25 seconds. Only applicable to visible light lasers (400-700nm). Class 2 laser, power limited to 1mW continuous, or higher power when the radiation time is less than 0.25 seconds, or the light is not spatially coherent. Intentional suppression of the blink reflex can cause eye damage. Many laser pointers and measuring instruments are Class 2 lasers.

Class 2M laser, is safe, if the optical instrument is not directly observed, the blink reflex will avoid injury. Like Class 1M lasers, the laser beam has a large diameter, or a large divergence angle, and the amount of light passing through the pupil cannot exceed the Class 2 limit.

Class 3R laser, which is safe when used with care, with limited beam viewing. With a Class 3R laser, it is possible to exceed the MPE, but with less potential for injury. Visible CW Class 3R lasers are limited to 5mW. Other wavelengths and pulsed lasers, subject to other conditions.

Class 3B lasers are dangerous if exposed directly to the eye, but no danger from diffuse reflection from paper or other rough surfaces. The AEL of the CW laser, the wavelength range from 315nm to the far infrared is 0.5W. 400-700nm pulsed lasers are limited to 30mJ. Other restrictions apply for other wavelengths or ultrashort pulse lasers. Protective glasses are required when viewing the class 3B laser beam directly. Class 3B lasers must be fitted with a key switch and safety

Full internal lock. A class 3B laser is used inside a CD or DVD recorder, but the recorder is class 1 because the laser doesn't come out of the recorder unit.

Class 4 lasers, the highest and most dangerous lasers, including all lasers exceeding Class 3B AEL. Class 4 lasers can burn the skin, direct, diffuse, or indirect viewing beams, causing devastating or permanent eye damage. These lasers can ignite flammable materials and present a fire hazard. These hazards also apply to indirect or non-specular beams, even from apparently rough surfaces - which means that great care must be taken when controlling the light path. Class 4 lasers must be fitted with a key switch and safety interlock. Most industrial, scientific, military, and medical lasers are Class 4 lasers.

The ANSI Z136.1 standard requires the parameters of the optical density (OD) of laser safety glasses, which can calculate the nominal hazard zone (NHZ), and the diffuse reflection can be observed with goggles.

Optical Density (OD) is a measure of the attenuation of energy passing through a filter. The higher the OD value, the higher the attenuation and the higher the protection level. That is, the OD value is a measurement of the laser energy passing through the filter.

OD is the reciprocal of the transmittance logarithm, OD = -log10 T, where T is the transmittance.

OD value transmittance% attenuation coefficient 0100%1110%1021%10030.10%1,00040.01%10,00050.00%100,00060.00%1,000,00070.00%10,000,00

2. European laser safety standard EN207/EN208/EC60825

The European laser safety standard EN 207/EN208, takes into account the optical density and the power/energy density of the laser when determining laser safety requirements. Similar to ANSI Z136.1, laser safety goggles must provide sufficient optical density to reduce laser power at or below the maximum allowable exposure (MPE), and must also provide damage threshold protection. According to EN207, laser safety goggles must be protected from direct internal beam exposure of the laser.

The EN207 standard requires goggles to be labelled with a degree of protection, detailing their damage thresholds, (eg 10600D L5 (L5 means a direct irradiation power density of 100MW/cm2 at 10600nm for 10 seconds).

The L ratio of EN207 is the damage threshold of the goggle material, that is, the power density that the goggles can withstand, and requires a laser stabilization test for at least 10 seconds (CW) or 100 pulses (pulse mode).

Working mode: The laser works in different modes with different power density characteristics and requires different protective glasses.

Mode Definition Pulse Width D Continuous (CW) Constant Power > 0.25 sI Pulse: Short Single or Periodic Energy Radiation > 1 us to 0.25 sR Bulk Pulse: Very Short Single or Periodic Energy Radiation 1 us to 1 nsM Mode Locked < 1 ns (Pico seconds and femtoseconds)

The scale is from L1 to L10, the number is the lower limit of optical density, Ln means OD>n, or T<10^(-n), T is the transmittance. The minimum scale for a given laser depends on the operating mode and wavelength.

Operating Mode Wavelength Range Maximum Laser Power Density Given Power Minimum Protection Class*D (Continuous) 180–315 nm1×10n-3 W/m²log(P) + 3315–1400 nm1×10n+1 W/m²log(P) - 11400 nm–1000 μm1×10n+3 W/m²log(P) - 3I,R (pulse)180–315 nm3×10n+1 J/m²log(E/3) - 1315–1400 nm5×10n-3 J/m²log( E/5) + 31400 nm–1000 μm1×10n+2 J/m²log(E) - 2M (ultrashort pulse)180–315 nm1×10n+10 W/m²log(P) - 10315–1400 nm1.5×10n -4 J/m²log(E/1.5) + 41400 nm–1000 μm1×10n+11 W/m²log(P) - 11*P in W/m², E in J/m². Level numbers should be rounded upwards.


1. 1064nm laser, pulse width 10ns, 100mJ/cm2 (103 J/m2). There is now a protective eyewear labelled DIR 1064 L5. The laser pulse width indicates that the R mode should be selected, the scale n=5, and the upper limit of the maximum laser power density is 5×102J/m2, indicating that the laser safety glasses are not suitable for protecting this kind of laser.

2. 780nm laser, continuous, power density 50 mW/cm2 (P = 500 W/m2), the surface needs D mode, the minimum protection level is log(500)-1=1.69, which is approximately equal to 2, at this time, safety glasses The minimum grade is D 780 L2.

From this scale, it can be inferred that the power density corresponding to n=0 is safe without protective glasses.

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