FEATURE
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The safety of protection

David Robson explores the latest advances in safety products for use in photonics environments

Recent developments in laser technology have made safety more important than ever before. Higher powers, greater intensities and a bigger range in the possible wavelengths of lasers mean that safety equipment has to provide stronger and more reliable protection, time after time.

Manufacturers need to be certain their products comply with the latest requirements of laser systems and applications. These changing requirements are also evident in the developments of the ANSI Z136 standards in America, which now includes the more complete classification system of lasers (see panel) currently adopted in Europe, with additional requirements for the more dangerous 3B and 4 lasers.

The new standards also include guidelines on the protection necessary for ultrafast lasers, which are gaining popularity all the time. With a greater frequency of pulses, more packets of energy can reach skin or eyes during any one period, causing greater damage. To ensure the amount of energy reaching a victim never reaches a dangerous level, the allowed length of exposure has been reduced.

Eyewear

These guidelines have also put pressure on the manufacturers of laser safety equipment. ‘The issue is to develop eyewear that covers both ultrafast pulses and ultrashort wavelengths,’ says Rich Greene, education director at the Laser Institute of America (LIA), which develops the ANSI standards.

Manufacturers now need to be sure that the materials used in safety eyewear can withstand new beam qualities, and that they can prevent too much light energy from reaching the eyes. Dielectric coatings in particular are providing some of this protection, as they are very efficient at reflecting certain wavelengths away from the eye, rather than simply absorbing the dangerous wavelengths, which can cause heating effects and functions less well at such high pulse rates.

This is not the only issue facing eyewear manufacturers, who are constantly trying to improve the comfort of their products. Somewhat surprisingly, people will not wear safety goggles if they are not comfortable, even if they are putting themselves in danger.

‘We try to minimise the size of the frames, and the nose piece can be adjusted to enhance comfort,’ says Catherine Gappenach, from GPT Glendale. They also try to make the frames stylish, and manufacturers are now offering spectacle prescriptions for the lenses, so they don’t have to be worn over existing glasses.


The XC laser safety eyewear from GPT Glendale includes a high-transmission filter for better vision

Visibility through the safety glasses can also be an issue. To provide the necessary protection, they need to filter out the wavelengths of the laser beam, to prevent it from reaching the eye. However, sometimes the filters will also remove other wavelengths of normal light, which would not be dangerous, but which are necessary to see. This reduces the quality of vision, so manufacturers are now trying to produce materials as wavelength-specific as possible. This is also useful for protection against beams from tuneable lasers, often used in medical applications, and which supply many different wavelengths. The coatings can be combined with absorbing filters to block different wavelengths, while still allowing enough visible light to be transmitted for good vision.

In medical applications, the patient as well as the doctor needs to be protected. To this end, GPT Glendale has produced a line of disposable eye shields, for use during laser cosmetic surgery. They look like white plaster, but include a metal lining, and are more hygienic than reusable alternatives.

Laser interlocking systems and safety curtains

The new classification of lasers in America will also affect the types of laser interlock systems that can be applied to laser systems. Laser interlock systems form a protection around a secure area where lasers are operating. If anyone enters the area, a trigger on the door tells the interlock system to stop the laser from outputting dangerous beams to prevent accidents. Some systems can even hold the door closed from the outside, to prevent lengthy experiments from being interrupted and ruined.

When installing a laser interlock system, it is important to consider the way it shuts down the laser beam, depending on both the type of laser and the application. The most basic type of system simply cuts out the power supply.

Another, alternative method uses a shutter mechanism in front of the laser aperture, which closes when the interlock is tripped. Paul Tozer of Lasermet says that this would be good for laboratory situations, with lasers in a fixed position, but it would not be useful for portable lasers as the shutter mechanism cannot be moved easily. It would also be impractical for high-power lasers, as the shutters can’t handle intense laser beams.

A third type of interface could shut down certain parts of the laser to prevent a beam being formed, while still running the essential elements, such as the cooling system, that prevent the laser from being damaged. According to Tozer, every 3B/4 laser should be manufactured with a special interlock connector that allows this. This type of system is suitable for portable lasers, with high powers.

As well as these functions, many interlock systems now include new technology to make them more useful. They could provide automatic illumination of safety signs above access points to the secure location. Many keep a track of the how the laser is functioning, and store this data in a computer so administrators can keep track of the status of the system. Some can also be accessed from remote locations.

Accessories and training

Lasermet also produces portable heavy-duty screens that can be moved to form an enclosure around a laser system. They are used during materials processing and manufacturing, to divide rooms and prevent accidents. They are inflammable, and can withstand intensities of 6kW/cm2.

All these precautions are absolutely essential in ensuring the safety of the scientists and engineers who work with laser equipment. However, these latest developments are only useful when they are applied to the right systems in the correct ways,

This is why education is vital for any application where lasers are used. ‘Many people don’t think they need someone specialised in laser safety,’ says Rich Greene of the LIA. ‘Then they react to a problem [after an accident’s happened], rather than being proactive beforehand.’ No matter how advanced laser safety equipment becomes, the weakest link in the chain will always be the humans that operate the laser systems.

Laser classes

Class 1 Safe.
Class 1M Safe provided optical instruments are not used.
Class 2 Visible lasers. Safe for accidental exposure (< 0.25 s).
Class 2M Visible lasers. Safe for accidental exposure (< 0.25 s) providing optical instruments, such as binoculars and telescopes, are not used.
Class 3R Not safe. Low risk.
Class 3B Hazardous. Viewing of diffuse reflection, from dull surfaces, is safe.
Class 4 Hazardous. Viewing of diffuse reflection is also hazardous.
Fire risk.

Information courtesy of Lasermet. A more detailed description can be found at www.lasermet.com/resources/classification_overview.htm