NIST Finds Many Protective Glasses Do Not Meet Specs for Shielding Light from Ultrafast Lasers

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High-power, ultrafast pulsed lasers increasingly supply light for biomedical applications and imaging, materials processing, industrial micromachining and more. But many laser eyewear products are not tested with ultrafast lasers and might not be providing adequate insurance for a technical workers who count on them.

Ted Heilweil

NIST researcher Ted Heilweil examines a siphon laser used in a OD testing.

The categorical reason for this conditions lies in a customary exam procedures and customary measurements widely followed by eyewear makers to set their product specifications. Those methods use low-power, continual light sources. As a result, they do not constraint many intensity hazards of tangible high-power, pulsed-laser operative conditions. Moreover, finish users usually intermittently exam how their eyewear performs in sold applications before to deployment.
Scientists during a National Institute of Standards and Technology (NIST) recently published a examine of 24 samples of protecting filters used in eyewear from 5 opposite manufacturers. They found that “some of them are good, though some did not perform even tighten to their possess specs when used with ultrafast lasers,” pronounced NIST researcher and examine co-author Ted Heilweil.

In one case, a filter claiming a certain visual firmness (indicating a suit of light it blocks) indeed supposing 10,000 times rebate light rebate than specified.* Others blocked a specific wavelength for that they were rated, though transmitted most some-more light during circuitously wavelengths.

Why does this happen? The answer is in a inlet of ultrafast pulsed lasers—those that evacuate light pulses with a generation totalled in femtoseconds (fs, a millionth of a billionth of a second, 10-15 s). Unlike a some-more informed “continuous-wave” lasers, or even pulsed lasers with longer pulses, whose outlay beams change usually in a really slight operation around a singular core wavelength, high-speed laser pulses lift a most wider camber of wavelengths. (See illustration.) As a pulses get shorter in time, a operation gets wider.

wavelength graph

Unlike continuous-wave lasers, that furnish usually one really slight wavelength, ultrafast pulsed laser bursts enclose light of many opposite wavelengths.

But eyewear manufacturers typically do not exam their lenses opposite ultrafast pulsed lasers, or magnitude how most light they retard during wavelengths nearby a rated wavelength. Indeed, some set their specifications but regulating laser light during all, relying on customary spectrometers with singular dimensions capabilities.

So, a researchers, primarily upheld by NIST’s Office of Safety, Health and Environment, began to examine how good a filters in protecting eyewear achieved in interlude light from femtosecond pulses.

Each of a 24 cosmetic or potion filter samples was rated by a manufacturer to retard light during a wavelength of 800 nanometers (nm, billionths of a meter, 10-9 m). The samples were tested during NIST regulating a general ultrafast titanium:sapphire laser with a core wavelength of 800 nm―infrared light usually next a threshold of tellurian vision―running during 80 million pulses per second and producing pulses durability about 40 fs.

Almost immediately, a NIST group and collaborators during Hood College in Frederick, Maryland, found “some flattering uncanny stuff,” Heilweil said. As expected, a pulses contained wavelengths trimming from 750 nm (visible red) to 900 nm (near infrared). Each filter responded differently to several sections of that span; one probable reason, a researchers speculate, is that a lenses might have opposite formulations of light-absorbing dyes.

Measurement set-up

Measurement set-up: Laser light from a left passes by several filters (green tabs), other apparatus (blue circle), and onto a sample, that is mounted where a rose-colored eyeglasses are here. The light that passes by a representation is totalled by a detector (not shown).

For example, one filter that blocked most of a light during 800 nm blocked usually one-hundredth as most during 847 nm. Many filters did not accommodate their possess specs when a core wavelength was altered by usually 1 percent. Some lenses were shop-worn by approach enlightenment in a few seconds, with formula trimming from nearby clarity to finish opacity. And some achieved intensely good opposite a whole operation of wavelengths.

The new examine is a initial of many that are needed, Heilweil said. “It’s some-more like a startup point. We’ve usually focused on one form of femtosecond laser. There are all opposite kinds, and tunable ones, too.”

Of course, a sorts of high-precision measurements conducted during NIST are not broadly available, and “it is unreal for laser eyewear manufacturers to settle their possess femtosecond laser-based exam facilities, that cover all probable outlay conditions of ultrafast systems,” Heilweil said. “So, we are perplexing to inspire manufacturers to use a best probable contrast laboratories to weigh their lenses.

“At a same time, and equally important, we need to get finish users to be some-more wakeful of a accurate wavelengths their lasers are producing. They need to exam their eyewear themselves—in a specific conditions and sold applications for that they will be used—before putting them on,” pronounced Heilweil.

Paper: C.J. Stromberg, J.A. Hadler, B.C. Alberding and E.J. Heilweil, Ultrafast laser eyewear protection: Measurements and precautions, Journal of Laser Applications. Published online Sep 2017. DOI: 10.2351/1.5004090.

* The NIST researchers conducted steady measurements of a visual firmness (OD) for any sample, mostly on opposite days and with opposite laser energy levels. The totalled values for a given representation were reproducible to within and or reduction 20 percent. OD is a logarithmic scale. A representation with an OD rating of 3 blocks 10 times some-more light than one with a rating of 2. Many of a variations in OD that a researchers totalled during opposite frequencies sundry by a cause of 100 or 1,000 or even more.

Source: NIST

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