Laser Goggle

Laser Goggle is the use of eye protection when operating lasers of classes 3B and 4 in a manner that may result in eye exposure in excess of the MPE is strongly recommended, and is required in the workplace by the U.S. Occupational Safety and Health Administration.

Laser Goggle in the form of spectacles or goggles with appropriately filtering optics can protect the eyes from the reflected or scattered laser light with a hazardous beam power, as well as from direct exposure to a laser beam. Laser Goggle must be selected for the specific type of laser, to block or attenuate in the appropriate wavelength range. For example, laser goggle absorbing 532 nm typically has an orange appearance, transmitting wavelengths larger than 550 nm.

Such laser goggle would be useless as protection against a laser emitting at 800 nm.

Furthermore, some lasers emit more than one wavelength of light, and this may be a particular problem with some less expensive frequency-doubled lasers, such as 532 nm "green laser pointers" which are commonly pumped by 808 nm infrared laser diodes, and also generate an intermediate 1064 nm laser beam which is used to produce the final 532 nm output.

If the IR radiation is allowed into the beam, which happens in some lower-quality green laser pointers, it will in general not be blocked by regular red or orange colored goggle designed for pure green or already IR-filtered beam.

Special YAG laser and dual-frequency goggle is available for work with frequency-doubled YAG and other IR lasers which have a visible beam, but it is more expensive, and IR-pumped green laser products do not always specify whether such extra protection is needed.

Laser goggle is rated for optical density (OD), which is the base-10 logarithm of the attenuation factor by which the optical filter reduces beam power.

For example, laser goggle with OD 3 will reduce the beam power in the specified wavelength range by a factor of 1,000. In addition to an optical density sufficient to reduce beam power to below the maximum permissible exposure (see above), laser goggle used where direct beam exposure is possible should be able to withstand a direct hit from the laser beam without breaking.

The protective specifications (wavelengths and optical densities) are usually printed on the goggles, generally near the top of the unit. In the European Community, manufacturers are required by European norm EN 207 to specify the maximum power rating rather than the optical density.

Laser Safety Goggle Guide

Goggle Technologies

Due to the unique characteristics of laser radiation (i.e. coherent, collimated and monochromatic) there is increased danger to the eyes. Therefore special optical filters that transmit 'normal' light but block laser light should be used.

Since laser light has a specific wavelength dependent on the laser active medium that emits light, goggles that match the wavelength and power of the specific source of laser radiation are needed.

Optical Density (OD)

Optical density is the attenuation of light that passes through an optical filter. The higher the OD value the higher the attenuation. The mathematic expression of optical density is the logarithm to the base ten of the reciprocal of the transmittance and is given by the following equation:

D = -log10 T

The optical density is a measure that indicates how many decimal places the transmission shifts at the required wavelength.

Selecting Laser Goggles

Laser Safety Officers (LSOs) should consider the actual working environment, viewing conditions and beam delivery systems when determining the most appropriate protective equipment needed to reduce potentially hazardous exposures to laser light. Laser safety eye protection options include spectacles, goggles, eye safety filters, full face shields, etc. Regardless of the specific type of eye protection system required to minimize potential exposures to levels below applicable MPEs the following types of light attenuation materials are generally used in their construction:

• Absorptive
• Reflective

Absorptive filters used in the construction of safety goggle products are typically made with either polycarbonate or glass materials, where light absorption at a given wavelength is a function of material thickness. This may be calculated in terms of OD by:

OD = -log10 Pd · lT() (D2/D1)

Where:

Pd = Reflection factor

I,()= Transmittance at thickness D1

D2 = Desired material thickness (mm)

D1 = Thickness of material for known internal transmittance (mm)

Polycarbonate goggle provides an excellent low cost, light weight safety solution but may have slightly lower OD's and Visible Light Transmission (VLT) values than filter glass or coated goggles.

Absorbing goggles generally provide higher optical densities, better VLT values but at a slightly higher cost per pair when compared to polycarbonate safety eyewear.

Thin-film coated goggles provide precise protection from specific wavelengths and can have excellent VLT values. This is done by applying physical vapor deposition (PVD) technology of dielectric materials upon various substrates. Precise (¼ wavelength thickness) vapor deposition of alternate HI-LO index of refraction dielectric coatings is applied directly to absorptive polycarbonate or glass filter materials. This provides laser protection by reflective as well as absorptive properties.

By capitalizing on the desirable absorptive and reflective characteristics of various filters laser goggle manufactures can bond or laminate two or more filters together using special UV-cured optical adhesive lamination technology. This extends the spectral protection range of a single type of goggle to cover a broader range of laser wavelengths.

Spectral scans of filters are completed over an entire range of wavelengths from which optical density data is generated and compared with published OD specifications to verify the absorptive or reflective properties. Filters will always exceed posted specifications but optical densities of wavelengths may vary slightly due to manufacturing processes.

The LSO shall review all goggle and approve it to be used with a laser.

Regardless of the type of goggles used in laser safety goggle the LSO should routinely examine them for integrity, proper labeling and storage. Goggle exhibiting gaps between the filter and frame, delaminating or other visible signs of damage should not be used; rather they must be repaired or replaced.

What's Optical Densities (OD)?

ANSI Z136.1 requires specification of laser safety Laser Goggles according to optical densities (OD), and allows a Nominal Hazard Zone (NHZ) to be calculated, outside which diffuse viewing Laser Goggles is allowed.

Optical Density (OD) is a measure of the radiation permitted to pass through a filter, or a measure of the attenuation of energy passing through a filter and it's determined by the filter.

The higher the OD value the higher the attenuation and the greater the protection level.

In other words, OD is a measure of the laser energy that will pass through a filter. I.e. and OD of 2.0 allows 1/100 of the laser light energy to pass through the filter. If you eyewear are marked with an OD of 4 or greater at 755 nm and your laser requires OD of 6 or greater at 755 nm your laser glasses will not provide enough protection from your laser and you could sustain a serious injury. OD is determined by several factors and should only be calculated by a expert.

OD is the logarithmic reciprocal of transmittance, expressed by the following:
D? = -log10 T ?, where T is transmittance.

OD (Optical Density)	Transmission in %	Attenuation Factor
0	100%	1
1	10%	10
2	1%	100
3	0.1%	1,000
4	0.01%	10,000
5	0.001%	100,000
6	0.0001%	1,000,000
7	0.00001%	10,000,000