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optical question

Started by John Larkin November 11, 2014

We will be firing up a semiconductor laser, at a couple of watts
optical output, around 1500 nm. The output will be small diameter and
well collimated, so it will be dangerous.

We can bolt our driver and the tiny laser to a metal block, and put
that into a metal box with a tight-fitting cover.

What should we do with the light? If we just hit an anodized surface,
a lot of it will bounce around. 

What do people do to dump laser power safely?

We'll probably want to sneak in a multimode fiber somewhere, to sample
the optical waveform, too. Maybe a milliwatt there.

Maybe a black version of an integrating sphere, with a tiny inlet?
Maybe a tapered tunnel, black anodized, an optical cul-de-sac?

Maybe use a tiny ball lens, or some diffuser, to scatter the light
some?


-- 

John Larkin         Highland Technology, Inc
picosecond timing   precision measurement 

jlarkin att highlandtechnology dott com
http://www.highlandtechnology.com

On 11/11/2014 2:07 PM, John Larkin wrote:
> > > We will be firing up a semiconductor laser, at a couple of watts > optical output, around 1500 nm. The output will be small diameter and > well collimated, so it will be dangerous. > > We can bolt our driver and the tiny laser to a metal block, and put > that into a metal box with a tight-fitting cover. > > What should we do with the light? If we just hit an anodized surface, > a lot of it will bounce around. > > What do people do to dump laser power safely? > > We'll probably want to sneak in a multimode fiber somewhere, to sample > the optical waveform, too. Maybe a milliwatt there. > > Maybe a black version of an integrating sphere, with a tiny inlet? > Maybe a tapered tunnel, black anodized, an optical cul-de-sac? > > Maybe use a tiny ball lens, or some diffuser, to scatter the light > some?
I would expect any matte black surface would absorb most of the light and what isn't absorbed would be diffused. If you think the beam might be too concentrated so that it would overheat the spot it is illuminating you might pass it through something like ground glass to disperse it first. I'm not sure how transparent glass is at that wavelength, but you get the idea I think. The main thing is to prevent reflections. You should be able to sample the beam directly or indirectly. -- Rick
On 11/11/2014 19:07, John Larkin wrote:
> > We will be firing up a semiconductor laser, at a couple of watts > optical output, around 1500 nm. The output will be small diameter and > well collimated, so it will be dangerous. > > We can bolt our driver and the tiny laser to a metal block, and put > that into a metal box with a tight-fitting cover. > > What should we do with the light? If we just hit an anodized surface, > a lot of it will bounce around.
Point it directly down a hole drilled into a copper block. There are tricks to get a black enough chemical finish on copper (or iron). Dumping a couple of watts isn't a problem provided it doesn't leak. The laser light can't hurt you if it can't get out. The dump block doesn't have to be very big to absorb a couple of watts.
> What do people do to dump laser power safely? > > We'll probably want to sneak in a multimode fiber somewhere, to sample > the optical waveform, too. Maybe a milliwatt there.
The main worry with laser light you can't see is that you can sustain serious damage without knowing it. There are no pain receptors in the eyes you only find out about 8 hours later when the immune response to dead cells kicks in. Same sort of problem with looking at the last crescent of the sun during a total solar eclipse.
> Maybe a black version of an integrating sphere, with a tiny inlet? > Maybe a tapered tunnel, black anodized, an optical cul-de-sac? > > Maybe use a tiny ball lens, or some diffuser, to scatter the light > some?
Dump it into a tube with a heat sink on it. An offcut of microbore plumbing pipe squeezed flat and then turned over at the end would probably be fine for dumping just a couple of watts. You ought to think about an interlock so the laser cannot be fired when the beam is not dumped into a safe load. I once walked in on someone with a He MIP flame with 700W of microwaves in a beautiful salmon pink flame with nothing between him and the radiation source. He defeated all the safety interlocks on the mesh faraday cage. Truly scary. -- Regards, Martin Brown
Den tirsdag den 11. november 2014 20.07.18 UTC+1 skrev John Larkin:
> We will be firing up a semiconductor laser, at a couple of watts > optical output, around 1500 nm. The output will be small diameter and > well collimated, so it will be dangerous. > > We can bolt our driver and the tiny laser to a metal block, and put > that into a metal box with a tight-fitting cover. > > What should we do with the light? If we just hit an anodized surface, > a lot of it will bounce around. > > What do people do to dump laser power safely? > > We'll probably want to sneak in a multimode fiber somewhere, to sample > the optical waveform, too. Maybe a milliwatt there. > > Maybe a black version of an integrating sphere, with a tiny inlet? > Maybe a tapered tunnel, black anodized, an optical cul-de-sac? > > Maybe use a tiny ball lens, or some diffuser, to scatter the light > some? >
a bottle of water? I believe water is highly absorbing at 1500nm or a stack of laser windows http://www.lasersafetyindustries.com/Laser_Safety_Windows_s/1.htm -Lasse
On Tue, 11 Nov 2014 19:37:29 +0000, Martin Brown
<|||newspam|||@nezumi.demon.co.uk> wrote:

>On 11/11/2014 19:07, John Larkin wrote: >> >> We will be firing up a semiconductor laser, at a couple of watts >> optical output, around 1500 nm. The output will be small diameter and >> well collimated, so it will be dangerous. >> >> We can bolt our driver and the tiny laser to a metal block, and put >> that into a metal box with a tight-fitting cover. >> >> What should we do with the light? If we just hit an anodized surface, >> a lot of it will bounce around. > >Point it directly down a hole drilled into a copper block. There are >tricks to get a black enough chemical finish on copper (or iron). >Dumping a couple of watts isn't a problem provided it doesn't leak. > >The laser light can't hurt you if it can't get out. The dump block >doesn't have to be very big to absorb a couple of watts. > >> What do people do to dump laser power safely? >> >> We'll probably want to sneak in a multimode fiber somewhere, to sample >> the optical waveform, too. Maybe a milliwatt there. > >The main worry with laser light you can't see is that you can sustain >serious damage without knowing it. There are no pain receptors in the >eyes you only find out about 8 hours later when the immune response to >dead cells kicks in. Same sort of problem with looking at the last >crescent of the sun during a total solar eclipse. > >> Maybe a black version of an integrating sphere, with a tiny inlet? >> Maybe a tapered tunnel, black anodized, an optical cul-de-sac? >> >> Maybe use a tiny ball lens, or some diffuser, to scatter the light >> some? > >Dump it into a tube with a heat sink on it.
That's a nice idea. A copper tube with some chemical blackening inside. Light would enter at a small angle and scatter and be absorbed along the way and not much could make it back from the end. The tube could be curved, too. Maybe put the fiber at the end to pick off what's left. -- John Larkin Highland Technology, Inc picosecond timing precision measurement jlarkin att highlandtechnology dott com http://www.highlandtechnology.com
John Larkin <jlarkin@highlandtechnology.com> wrote:

 
> We will be firing up a semiconductor laser, at a couple of watts > optical output, around 1500 nm. The output will be small diameter and > well collimated, so it will be dangerous.
> We can bolt our driver and the tiny laser to a metal block, and put > that into a metal box with a tight-fitting cover.
> What should we do with the light? If we just hit an anodized surface, > a lot of it will bounce around.
> What do people do to dump laser power safely?
> We'll probably want to sneak in a multimode fiber somewhere, to sample > the optical waveform, too. Maybe a milliwatt there.
> Maybe a black version of an integrating sphere, with a tiny inlet? > Maybe a tapered tunnel, black anodized, an optical cul-de-sac?
> Maybe use a tiny ball lens, or some diffuser, to scatter the light > some?
Phil will have the best approach. While you are waiting for him to come online, here's some methods from Wikipedia: Optical beam dumps An optical beam dump is an optical element used to absorb a beam of light. Major design concerns in a beam dump typically include the management and reduction of back reflections and scattering as well as the dissipation of heat generated by absorption. For low-power systems and less demanding applications, the device can be as simple as a piece of black velvet or flock paper glued onto a stiff backing, but higher- power beam dumps must often incorporate more elaborate features to avoid back-reflection, overheating, or excessive noise. Dumping the beam with a simple flat surface may scatter unacceptably large amounts of light for some applications, even though the direct reflection may be effectively reduced. To minimize scattering, it is common to use deep, dark cavities lined with an absorbing material to dump the beam. A particularly simple and relatively inexpensive approach is to use a stack of razor blades with the sharp edges facing the beam, so that the spaces between the blades form very deep cavities from which little light escapes. A commonly available type of beam dump suitable for most medium-power lasers is a cone of aluminum with greater diameter than the beam, anodized to a black color and enclosed in a canister with a black, ribbed interior. Only the point of the cone is exposed to the beam head-on; mostly, incoming light grazes the cone at an angle, which eases performance requirements. Any reflections from this black surface are then absorbed by the canister. The ribs both help to make light less likely to escape, and improve heat transfer to the surrounding air. http://en.wikipedia.org/wiki/Beam_dump
On Tue, 11 Nov 2014 14:21:21 -0500, rickman <gnuarm@gmail.com> Gave us:

>I would expect any matte black surface would absorb most of the light >and what isn't absorbed would be diffused.
You really don't know anything about laser power levels, do you?
On 11-11-2014 20:07, John Larkin wrote:
> > > We will be firing up a semiconductor laser, at a couple of watts > optical output, around 1500 nm. The output will be small diameter and > well collimated, so it will be dangerous. > > We can bolt our driver and the tiny laser to a metal block, and put > that into a metal box with a tight-fitting cover. > > What should we do with the light? If we just hit an anodized surface, > a lot of it will bounce around. > > What do people do to dump laser power safely? > > We'll probably want to sneak in a multimode fiber somewhere, to sample > the optical waveform, too. Maybe a milliwatt there. > > Maybe a black version of an integrating sphere, with a tiny inlet? > Maybe a tapered tunnel, black anodized, an optical cul-de-sac? > > Maybe use a tiny ball lens, or some diffuser, to scatter the light > some? > >
I wouldn't risk anything here, it's hard to verify the proper operation of a beam dump, when the light is invisible. Buy a readily available optical beam dump. Example: http://www.edmundoptics.com/lasers/laser-mechanics/metric-beam-dump/2193 (probably available cheaper from other vendors, was just the first link I found) Klaus
On Tue, 11 Nov 2014 19:37:29 +0000, Martin Brown
<|||newspam|||@nezumi.demon.co.uk> Gave us:

>Point it directly down a hole drilled into a copper block. There are >tricks to get a black enough chemical finish on copper (or iron). >Dumping a couple of watts isn't a problem provided it doesn't leak. > >The laser light can't hurt you if it can't get out. The dump block >doesn't have to be very big to absorb a couple of watts.
Good suggestion. Instead of glass, I would use some high purity industrial diamond thingy. Diamond has the best heat characteristic Of anything (short of neutron star material), and can handle a lot of laser energy before getting all violent about it.
On Tuesday, November 11, 2014 11:07:18 AM UTC-8, John Larkin wrote:
> We will be firing up a semiconductor laser, at a couple of watts > optical output, around 1500 nm. The output will be small diameter and > well collimated, so it will be dangerous. > > We can bolt our driver and the tiny laser to a metal block, and put > that into a metal box with a tight-fitting cover. > > What should we do with the light? If we just hit an anodized surface, > a lot of it will bounce around. > > What do people do to dump laser power safely?
Tried razor blades? http://www.mazepath.com/uncleal/blade.htm Mark L. Fergerson