Eye Safety with Lasers: 15 mW & Fiber Coupling

[silin]

A question to people coupling lasers to optical fibers. What is the power and exposure time of laser beam directed in the eye which is considered dangerous? The ones I´m currently working with are 15 mW. Are there any ways to couple laser beam to a fiber without having to look into another end of it (my photometer isn´t sensitive enough for small intensities)?

 

[brewnog]

Power and exposure time aren't everything, eye safety is also dependent on the frequency of the laser beam.

What class is your laser? That will be the best way to determine what safety precautions should be taken with regards to eye safety.

 

[silin]

It's the class III laser, there are two of them: one with 470nm wavelength, second with 635nm.

 

[brewnog]

DON'T look directly into the beam of a Class III laser, especially since at 15mW, it falls into the Class III (b) category. Find another way.

 

[silin]

I don't look directly into the beam coming from the laser head, but at the one coming from the optical fiber, in which I'm trying to couple the beam. If I measure the intensity of this light, it's about 0.1 mW at first, as soon as it get this big, I start to use my photometer. Is it still dangerous this way?

 

[silin]

Can you give a reference where to read more on the issue of laser safety? Thank you.

 

[ZapperZ]

Since you did not say where you are, nor in your profile, this may not apply to you. But if you are doing this as part of your work, OSHA will not be very happy with either you or your employer for not adequately training you on the safety requirements of handling such laser.

No Class IIIa or IIIb, and certainly not Class IV lasers, should ever be looked at with the naked eye. And it is required that suitable eye protection be worn when working with such lasers. Even Class II lasers (those used in many laser pointers) should not be looked at with one's eye for any "prolonged" of time.

Zz.

 

[silin]

Well, you're right, I'm not too happy about my professor too, not having told me anything about the laser safety, that's whay I'm looking for this info myself. The PhD student who supervises my work also does the laser coupling this way (and actually his eyesight isn't very good as I notice). Should I then demand from them to buy more sensitive equipment? Actually I'm working in Germany and the industry doctor said they don't take any responsibility concerning laser damage.

 

[brewnog]

Well, you're right, I'm not too happy about my professor too, not having told me anything about the laser safety, that's whay I'm looking for this info myself. The PhD student who supervises my work also does the laser coupling this way (and actually his eyesight isn't very good as I notice). Should I then demand from them to buy more sensitive equipment? Actually I'm working in Germany and the industry doctor said they don't take any responsibility concerning laser damage.

I don't know about German health and safety law, but I would definitely refuse to carry out work with these lasers until the proper safety precautions and procedures have been implemented. Demand proper safety training, and demand the necessary equipment to carry out your work safely.

I had to watch a 40 minute laser safety video before I was allowed to work even with Class II lasers, I'm quite surprised that you haven't been made to do the same.

Good luck!

 

[brewnog]

Oh, here's a pretty comprehensive laser safety manual, assuming that you haven't been provided with such a thing.

http://www.ehrs.upenn.edu/programs/laser/laser_manual.html

 

[Claude Bile]

Use a beamsplitter to divert a fraction of the beam onto a screen that you can view, as viewing diffuse reflections is only dangerous when viewing class IV lasers. Maximise the spot intensity, then use your photometer. Never, ever under any circumstances look directly into the beam, apart from being dangerous it is a completely unnecessary risk.

Don't know what the workplace safety laws are in Germany but in Australia, if you think you need a piece of equipment that makes your job safer, your employer (or your academic institution) is obliged to provide such equipment. This would include remote detection equipment.

Laser safety is not something you should muck around with, if you think there is significant risk, contact your university's Ocupation Health and Safety department and demand that laser safety protocols be adhered to.

Claude.

 

[silin]

Thank you for the information. I think in the lab I work they are not following safety with class IV lasers too, if you say even its reflection is dangerous, because these reflections are over the whole place there. And I didn't like that such bright and powerfull lasers aren't somehow put into some cases to protect eyes. These are mostly biologists with whom I work, but it doesn't assume that they should be ignorant about such importans safety issues. I'm very angry to find out that they just didn't inform me about anything! I'll ask the secretary about safety instructions about the lasers today.

 

[silin]

Use a beamsplitter to divert a fraction of the beam onto a screen that you can view, as viewing diffuse reflections is only dangerous when viewing class IV lasers. Maximise the spot intensity, then use your photometer.

You mean beamsplitter on the other end of the fiber? But what for if you can just direct it at the screen to see how bright it is. The problem is that when you just start with coupling at first you see just nothing. Are you supposed just to be turning the screws randomly till something comes out or are there more intelligent ways to do it?

 

[Claude Bile]

Disregard the beamsplitter thing, you are right, you can just put it on a screen. You only really need a beamsplitter if you are trying to monitor something else at the same time.

I am assuming you are using a lens to couple light into the fibre in which case, you should set the input end of the fibre as close to the focus as possible. You should use a high magnification objective to couple light, one that will give you a beam waist of around 8 microns for a single-mode fibre (A 5x or 10x should be ok for this).

Next, when performing the lateral alignment, keep an eye on the input end of the fibre, when the input end glows, this means you are coupling light into the cladding (which is a good start). Maximise the glow at the input along one axis (This will hopefully centre the fibre on that axis). As you sweep across the other axis, you should be very close to coupling into the core, hopefully you should see enough light at the output to optimise the alignment from there.

There is also a heap of equipment available designed to make this process less painful, or even unnecessary, so if you are wasting heaps of time coupling light into a fibre, maybe you should ask your professor about alternative arrangements that can be made.

Claude.