Safely Visualize Laser Spot

[benjamingrantdu]

Hi All
recently set up a 445 nm laser system. I'm running it off of *relatively* low power (<100 mw) - in fact right now I have it set <10 mW. The problem i'm having is I need to visualize my beam, to focus it down to the proper spot size I need for a research application, but when I put my goggles on I can't see it anymore. Any suggestions on how to see it? I used a green flourescent standard that emits green light but since my goggles don't protect in the green spectrum I'm a little worried about damaging my eyes that way. Is that a legitimate worry? Also, is IR light something you need to worry about for 445 nm lasers? I'm paranoid about eye safety and have, in moments of frustation, looked at the beam with my goggles off to try and see what shape it is in but I'm always very worried afterwards i hurt my eyes. In fact my left eye is watery/itchy now which is probably unrelated but I keep worrying about it. Anyway, I want to keep my goggles on 100% of the time so I can stop worrying but I need a way to see the spot somehow. Any suggestions? I'm using the LG3 glasses found here http://www.thorlabs.com/NewGroupPage9.cfm?ObjectGroup_ID=762

 

[InfinitusEquitas]

If you're using a diode based laser, you have nothing to worry about with a 445nm laser... since it will emit only 445nm.

Have the beam terminate on a black, matte surface.

There is no danger in observing the beam of a 100mW laser (or a 2W for that matter). If your eyes are watery/itchy it's most likely from allergies, and simply being tired.

To see the dot, with the goggles on, you will need to either increase the power, or get goggles with a lower OD rating.

To see the beam you will need to take off your goggles.

What exactly are you trying to do in your research application? If you're using a university lab, have someone familiar with laser safety instruct you in proper use.

 

[benjamingrantdu]

Sorry my question about the IR was dumb, I had just read something and wasn't thinking clearly. I'm actually sick and I'm pretty sure that is why my eye is bothering me. I have seen the dot a couple of times but only at low power (around 10 mW). I'm using the micro flex v5 driver and have noticed that when you first hit the switch and power the laser on there's quick bright surge, where the power is definitely higher than what you're running at - so I guess it's possible during turning it on I somehow damaged my eye.

Anyway, paranoia aside, what I'm trying to do is light a fiber optic cable (1 mm in diameter) for a flourescent imaging application. Because the optic cable is being used to both carry the excitation light from the laser and receive the emitted light, the cable isn't directly in front of the laser but is about 60 mm away after a dichroic mirror and a 40x objective (which is used to collect the light from the fiber). Unfortunately, if I collimate my light with the aixiz glass laser lens, the beam size is too small to entirely fill the back aperature of the 40x objective, and thus doesn't evenly fill the fiber optic cable. I'm working on building a simple beam expander to fix this, but I kind of need to know the spot size I'm getting coming out of the objective. I could turn the power up on the laser or get lower OD protection I suppose.

 

[InfinitusEquitas]

Gotcha... well sort of anyway. Turn up the power and use a non reflective matte surface. You will be able to see either the dot itself, or the fluorescence from it. (Not sure with those goggles.)

 

[Apocalypse]

10mW of fluorescence shouldn't harm the eye would it? There are many different kinds of fluorescent sticky notes you can use that have different colors though.

 

[willpine]

Those two questions seem to be different.
Can you not connect them(the fiber optic and laser source) for some reason? There is some optics that would help get you there, you know.like glass shapes and lenses Or use some type of funnel effect maybe.


If not, use <5 (less than) red laser to line up somewhat and you can roughly see how big the spot , divergence, is. Also, use something to diffract ,I think, in the air. So put something in the air like a fog machine, smoke, mist, spray cans (laser beam spray) link courtesy of daguin from old post in 09'.
ESL | eBay
The old thread is this one kinda cool. http://laserpointerforums.com/f49/where-buy-laser-beam-visualizer-spray-33964.html

OR you could use a filter or detection card that will
Light up when you hit it. They have different types for diff wavelengths.

 

[benjamingrantdu]

Those two questions seem to be different.
Can you not connect them(the fiber optic and laser source) for some reason?

I can't connect them due to design constraints. The fiber is also collecting the signal emitted from the fluorescing tissue sample which goes through a separate path. Using a dichroic mirror, the excitation light goes through a different path than the emitted light. Anyway, the point is, the laser diode cannot be right next to the fiber optic cable, it needs to be about 75 mm away. I can figure out that part but I just need to be able to see what the current spot size is.

As for using a red laser diode, I don't think the spot size for the two lasers will be equivalent so it won't really help me to know if i'm expanding the beam enough or not.

 

[benjamingrantdu]

10mW of fluorescence shouldn't harm the eye would it? There are many different kinds of fluorescent sticky notes you can use that have different colors though.

Well, if I used a fluorescent sticky note that IS protected by my goggles then I won't be able to see it anyway, so it doesn't help too much. The fluoresecence isn't coherent so I don't think it is actually too dangerous to look at, but I'd like confirmation of that.

 

[nouthyella]

I have seen the dot a couple of times but only at low power (around 10 mW). I'm using the micro flex v5 driver and have noticed that when you first hit the switch and power the laser on there's quick bright surge, where the power is definitely higher than what you're running at - so I guess it's possible during turning it on I somehow damaged my eye.

It is vanishingly unlikely that this could have happened, looking at the diffuse dot of even a 100mW, except at very close range in a dark room, would be extremely unlikely to cause any kind of damage, even temporary. The gain of the 100mW dot is far lower than that of even a torchlight, let alone a laser.

The diffuse reflection should in no event cause you any discomfort. If it does, stop viewing it, viewing a diffuse reflection is no more dangerous than waking up with the sun in your face, you are protected by the blink reflex under those circumstances.

I have "etched" quite a few pieces of plastic/wood with my blue >1w while wearing goggles, and in all of these events the dot was visible as a whitish-orangish, very pale patch on the material. I assumed it was due to incandescence. You could try putting a dark material (black paper?) into the beam path while wearing goggles to see if you can visualise that with your laser.

 

[benjamingrantdu]

Thanks! Yeah my eyes weren't hurt, just paranoia. I will say wearing the goggles for a long period of time causes my eyes to feel tired -- like if you were reading small font on a computer screen. Not like pain really but just a little tired at the end of the day.

I ended up just turning the power up to 70 mW and I do use a black piece of paper (if light is diffuse then I end up using a lighter color matte business card) - but black is best if it shows up. Thanks for the suggestions
Ben

 

[InfinitusEquitas]

Glad they helped.