safety glasses/goggles?

[White-Light]

Removed due to James's excellent detailed post below.

[norty303]

Ok, seeing as this thread is getting some traffic, and its 'on topic', I'll put my question here:

Does anyone have a source for cheap 808nm or broadband IR filters/glasses that I can use for re-aligning a 500mW 532 DPSS head with probably a 2W pu,p or so?

The module is a) cheap, and the technology is about to become relatively obsolete once these 520nm diodes become affordable, so I really don't want to spend a load on glasses I won't need anymore, or are as costly as a new head.

Fank U

[JStewart]

Whitelight's post isn't really correct, so here are some facts that may help those interested.

OD stands for Optical Density; it is the negative of the logarithm of the transmittance of the eyewear. Which put simply, is the power of ten by which the optical radiation is reduced by.

e.g. an OD of 2 = 10^2, so the reduction is 100x
similarly, an OD of 3 = 10^3, so the reduction is greater, being 1000x.

For alignment work of visible lasers at close working distances, it is often appropriate to use the accidental exposure condition as the protection factor, which is the Class 2 AEL limit. i.e. 1mW.

So, without the need for expensive MPE meters, or having to do special conversions from watts to 'protection factors', a simple calculation can be performed to determine the required OD.

e.g. someone working with a 532nm green laser, outputting 1W, needs to reduce the power at the eyes to 1mW, so the reduction factor is 1000x or 10^3 to get to 1mW = OD 3.

If greater protection is required, e.g. for non-alignment work, then the Class 1 AEL would be more appropriate, so the limit would be 0.39mW. Again, all that is needed is some simple maths to figure out the minimum OD.

You can use the following formula

OD = -log(Exposure Limit / Laser Power)

with Exposure Limit being with 1mW or 0.39mW
and Laser Power being the output power of the laser.

Remember that the OD is normally only applicable to a particular wavelength.

Laser safety eyewear is very wavelength specific with large reductions occurring in some parts of the spectrum, and much lesser reductions taking place in other regions. This is why it’s important to check with the manufacturer as to what the OD is for the particular wavelength of laser you need to protect against. Manufacturers will have this information available.

Other considerations…

As well as the OD, the damage threshold of the filter material has to be taken into account. (this is why, even if the OD on some ebay unbranded non-CE marked $10 eyewear looks to be valid, I would be very wary of actually using it to protect my eyes!)

In Europe is it not legal to use non-CE marked eyewear in the workplace. This is because properly CE classified eyewear has to go through rigorous tests for, among other things, how easily the eyewear filters can be damaged by lasers hitting the lenses.

The two safety standards that are used for testing eyewear performance to demonstrate CE compliance are EN207 and EN208.

There is no point having eyewear that can reduce power levels of light hitting the filters, only for actual laser exposure to reduce the effectiveness of the filtering during use. Whether it be an acute exposure that causes the filter damage, or something that starts to deteriorate over time through repeated exposure.

Hopefully this has helped to explain how the required ODs can be determined from the power of visible lasers that we are working with, and the importance of eyewear quality and compliance for damage threshold.

EN207 and EN208 Differences.

As mentioned above, there are two European Safety Standards for laser safety eyewear.

EN207 is intended to offer protection against all laser exposure (visible and non-visible).
EN208 is intended to offer alignment protection.

EN208 is only applicable to visible lasers as it relies upon the aversion response.

The EN standards use the same concept of optical density to convey how much they reduced light by. But they do present it in a slightly different way.

EN208
Keeping with alignment for the moment, (EN208), a ‘scale number’ is used to make selection of eyewear very straightforward to users. The scale is a number prefixed by the letter ‘R’ and is as follows:

Scale Max Laser Power (W)
R1 0.01
R2 0.1
R3 1
R4 10
R5 100

The scale number tells users the maximum power of laser that can be used with the filter in the eyewear.

Keeping in mind what I said earlier about limiting the power to 1mW at the eye (the equivalent to 25.4W.m-2, (the same as 2.5mW.cm-2 for the Americans)), you can see that the scale number is essentially the OD number calculated earlier but presented differently e.g. R3 uses an OD 3 filter to attenuate from 1W down to 1mW.

This is only valid for visible lasers only – because of the reliance on the aversion response.

EN207
This standard is intended for all laser types, visible and non-visible, where intentional viewing of the beam is not required. Eyewear uses a ‘scale number’ again to indicate the level of protection it gives, but it differs from that used for alignment laser protection. This time the number is prefixed by an ‘L’. The scale is often referred to as the ‘L number’.

For CW beam exposure each L number offers protection against a specific maximum power density (or irradiance to give it its correct term). This does change depending on the wavelength. But for common wavelengths between 315nm and 1400nm, the same irradiance applies.

Scale Max Irradiance (W.m^-2)
L1 100
L2 1,000
L3 10,000
L4 100,000
L5 1,000,000
L6 10,000,000

Essentially, what the L number is doing in each case is limiting the irradiance that reaches the eye to 10W.m-2. (the CW MPE).

EN207 additionally specifies some other markings which are used to designate the laser type / exposure duration.

D = Continuous Wave (CW) Laser >0.25s
I = Pulsed Laser >10^-6s to 0.25s
R = Giant-pulsed Laser >10^-9s to 10^-6s
M = Mode-coupled Pulsed Laser <10^-9

I think in most cases, users on this forum will be using CW lasers.

Good quality laser safety eyewear providers will be aware of all the things discussed, and more, and will be able to recommend to you the most suitable eyewear for your particular laser.

In the meantime I hope this note has been of use.

James

[norty303]

Ok, so to reduce a 2W 808nm pump to safe levels I'd need OD4, as OD3 would only reduce to 2mW/cm? Correct?

[Galvonaut]

Thanks for the great post James. Most informative

Keith

[dsli_jon]

..what I wanna know is where can I get cipher's life-saving / eye-protecting vaccine?

[turbohead]

Ok, seeing as this thread is getting some traffic, and its 'on topic', I'll put my question here:

Does anyone have a source for cheap 808nm or broadband IR filters/glasses that I can use for re-aligning a 500mW 532 DPSS head with probably a 2W pu,p or so?

I purchased a pair of these:

http://www.ebay.com/itm/Laser-Protec...item19d166c6de

I viewed the IR with night vision monocular. They clearly block the IR when I place the goggles in front of the monocular. I would say they work and are the cheapest I could find.

It appears they are on "sale."

[cipher0]

Link is invalid

..what I wanna know is where can I get cipher's life-saving / eye-protecting vaccine?

Never mentioned an eye protecting vaccine, for the rest, you probably have been vaccinted already as a child, i wouldnt worry if i was you

[dsli_jon]

...Never mentioned an eye protecting vaccine...

[The_Doctor]

I made an 'IR sniffer' out of an N connector adapter, a BNC plug, a drawing pin, a small button cell, a phototransistor, a 'hyperbright' green LED and the front end of a dark, opaque IR emitting LED. And a few other gubbinses.

The BNC plug gets the photo-transistor, and pointing right at its nose is the nose of the IR LED's plastic, after it was cut off the rest of the LED and ground nicely flat. Light goes in the flat end, but if it's visible it gets blocked there. IR goes through and is coupled efficiently straight into the photo-transistor. The button cell and the bright green LED are in series, and 'off' means unplug the BNC sensor bit. This allows other sensors to be built. I used it in the past to detect the IR when repairing VCR's. It's very sensitive despite having no active gain circuit. Put a piezo tweeter across the bright LED and you can even hear pulse trains! It's a great diagnostic widget given how crude it is. I still have it, and after twenty years I have not yet had to replace that button cell.

With a laser, you'd just hold it anywhere you might put an eye, and point it at the likely source of IR. All kinds of combinations of distance and directin can get instantly scoped this way, and that's very useful information! If the laser is meant to be green you might want to use a hyperbright red LED for better visibility. This IR sniffer trick will be good for 1064 and 808nm, and the dispersion pattern is likely to tell you which you're pointing at.

It's sensitive to the point that if it will not light up you can be damn sure that there is no risk of eye damage by near IR at the location occupied by its sensor, but always point in other directions just in case a reflection is passing through in another direction. Once you get used to it, it will tell you more than a camera, and at less cost and risk of equipment damage.