Enclosure of the laser equipment or beam path is the preferred method of control, since the enclosure will isolate or minimize the hazard.  When engineering controls do not provide adequate means to prevent access to direct or reflected beams at levels above the MPE, it may be necessary to use personal protective equipment.  Note that use of personal protective equipment may have serious limitations when used as the only control measure with higher power Class 4 lasers or laser systems.  The protective equipment may not adequately reduce or eliminate the hazard and may be damaged by the incident laser radiation.

 Protective Eyewear

 

Protective eyewear is necessary for Class 3 and 4 laser use where irradiation of the eye is possible.  Such eye protection should be used only at the wavelength and energy/power for which it is intended.  Eye protection may include goggles, face shields, spectacles or prescription eyewear using special filter materials or reflective coatings (or a combination of both) to reduce exposure below the MPE.  Eye protection may also be necessary to protect against physical or chemical hazards.

The following factors should be considered in selecting the appropriate laser protective eyewear:


  •  wavelength(s) of the laser output
  •  potential for multi-wavelength operation
  •  radiant exposure or irradiance levels for which protection (worst case) is required
  •  exposure time criteria
  •  MPE
  •  optical density (OD) requirement of the eyewear filter at laser output wavelength
  •  angular dependence of protection afforded
  •  visible light transmission requirement and assessment of the effect of the eyewear on the ability to perform tasks while wearing the eyewear
  •  need for side shield protection and peripheral vision
  •  radiant exposure or irradiance and the corresponding time factors at which laser safety eyewear damage (penetration) occurs, including transient bleaching
  •  need for prescription glasses
  •  comfort and fit
  •  degradation of absorbing media, such as photobleaching
  •  strength of materials (resistance to mechanical shock or trauma)
  •  capability of the front surface to produce a hazardous specular reflection
  •  requirement for anti-fogging design or coatings

 

Laser Eye Protection Selection Process

1.   Determine the wavelength of the laser.  Eye protection is wavelength-specific.  Eyewear that provides protection for CO2 lasers will not necessarily protect against Nd:YAG lasers.

2.   Determine the maximum anticipated viewing duration. Viewing duration usually fall into one of three categories:

a)     Unintentional, accidental exposure to visible lasers(400-700 nm), use 0.25 seconds

b)     Unintentional, accidental viewing of near infrared (700-1000 nm) beams, use 10 seconds

c)     For all other lasers, use 600 seconds or laser on time, up to 8 hours.

3.   Determine the maximum irradiance or radiant exposure to which the eye may be exposed.  Consider the following:

a)     If the emergent beam is not focused down to a smaller spot and is greater than 7 mm in diameter, the emergent beam radiant exposure/irradiance may be considered the maximum intensity that could enter the eye. 

b)     If the beam is focused after emerging from the laser or if the beam diameter is less than 7 mm, assume that all of the laser energy/power could enter the eye.  In this case, use the columns titled Maximum Output Power/Energy in the table below.

4.   Determine the optical density needed.

5.   Select the type of eye protection needed.  Laser eye protection is available in the form of glasses and goggles.  The lens may be made out of glass or crystalline filter material or plastic.  Generally, glass or crystalline lenses are recommended for harsh environments, such as areas where solvents and corrosives are used.

6.   Test the eye protection.  Always check the integrity of the lens before use.  At very high beam intensities, filter materials become bleached out or otherwise damaged.  A continuous wave power exceeding 10 W can fracture glass and burn through plastics.

 

  

Selecting Laser Eye Protection for Intrabeam Viewing for 400 - 1400 nm Wavelengths

Q-Switched
(1 ns - 0.1 ms)
Non-Q-Switched
(0.4 ms - 10 ms)

CW Momentary View (0.25 s to 10 s)

CW Starting (more than 3 hours)

Attenuation Factor

Max Output Energy (J)
Max Beam Radiant Exposure (j/cm^2)
Max Laser Output Energy (J)
Max Beam Radiant Exposure (J/cm^2)
Max Power Output (W)
Max Beam Irradiance (W/cm^2)
Max Power Output (W)
Max Beam Irradiance (W/cm^2)
10
20
100
200
na
na
na
na
100,000,000
1
2
10
20
na
na
na
na
10,000,000
10^-1
2x10^-1
1
2
na
na
na
na
1,000,000

10^-2
2x10^-2
10^-1
2x10^-1
na
na
10^-1
2x10^-1
100,000
10^-3
2x10^-3
10^-2
2x10^-2
10
20
10^-2
2x10^-2
10,000
10^-4
2x10^-4
10^-3
2x10^-3
1
2
10^-3
2x10^-3
1,000
10^-5
2x10^-5
10^-4
2x10^-4
10^-1
2x10^-1
10^-4
2x10^-4
100
10^-6
2x10^-6
10^-5
2x10^-5
10^-2
2x10^-2
10^-5
2x10^-5
10

 

Other Protective Equipment

It is important that protective equipment such as beam stops, shields, safety interlocks, and warning lights and horns be maintained in proper operating condition and be utilized whenever indicated to prevent harmful exposure to laser radiation. 

 

Special Controls for UltraViolet and Infrared Lasers

Since infrared (IR) and ultraviolet (UV) wavelengths are normally invisible, particular care must be taken when using these types of lasers.  In addition to the recommended control measures that apply for each laser classification, the following should also be employed:

Infrared

1.  The collimated beam from a Class 3 laser should be terminated by a highly absorbent backstop wherever practicable.  Many surfaces which appear dull visually can act as reflectors of IR.

2.  The beam from a Class 4 laser should be terminated in a fire resistant material wherever practicable.  Periodic inspection of the absorbent material is required since many materials degrade with use.

3.  Areas that are exposed to reflections from Class 3 or 4 lasers, at levels above the MPE, should be protected by appropriately screening the beam or target area with IR absorbent material.  This material should be fire-resistant for use with Class 4 lasers.

UV

1.  Exposure to UV should be minimized by using shield material which attenuates the radiation to levels below the appropriate MPE for the specific wavelength.

2.  Special attention should be given to the possibility of producing undesirable reactions in the presence of UV, for example, ozone formation. 

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