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optical question

Started by John Larkin November 11, 2014
Oxalic Acid based standard Gun Bluing makes a ugly blue/black coating on Cu. Possibly just what you need. So use a 4" length of straight copper into a 90' El 
that has a copper cap on the end. 

Watch for back reflections into laser diodes and fibers. Catastrophic Optical Destruction (COD) gets expensive quick. Your laser will become a expensive  LED if the back reflection is strong and properly phased.

Steve 
On Wednesday, November 12, 2014 12:06:58 PM UTC-5, John Larkin wrote:
> On Tue, 11 Nov 2014 20:53:19 -0800 (PST), "duedilligence@null.com" > <sroberts6328@gmail.com> wrote: > > >I should clarify, my bead attenuators use the small, clear, necklace beads with the hole in the center to provide scatter. These are not pure spheres, they are well suited to diffusion and scattering. > > > >The depth of the beads controls the attenuation. You may also crush the beads for greater attenuation per a given volume. Or add silica sand. > > > >When I use the bead scattering scheme with a window, I tilt the ghost beam into another dump. > > > >At 1-2 Watts CW this is very feasible. At higher powers professional discretion is advised and a safety case should be made. > > > > A good paper on Maximum Permissible Exposure calculations is here: > >http://safety.uchicago.edu/files/Laser%20MPE%20and%20NHZ%20Calculations.pdf > > > >Steve > > Sand packed in a metal tube might work, too. I could poke the probe > fiber in from the other end, until I get a reasonable signal level to > scope. > > There might be a few picoseconds of scattering, but that wouldn't be a > problem in the current application. > > The blackened copper tube would work similarly; poke in the fiber > until the coupling is good. Ebay sells liquid brass/copper blackening > stuff, and there's a great hardware store a couple of blocks away. >
If you don't like the razor blade thing, we use to use aquadag to coat the inside of big pumping tubes for low temperature stuff. It's black graphite stuff and should absorb in the IR. George H.
> > -- > > John Larkin Highland Technology, Inc > > jlarkin att highlandtechnology dott com > http://www.highlandtechnology.com
On Tue, 11 Nov 2014 16:45:32 -0500, Phil Hobbs
<pcdhSpamMeSenseless@electrooptical.net> wrote:

>On 11/11/2014 03:11 PM, Tom Swift wrote: >> 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. > >Cone dumps work at about the -40 dB level, but black anodize isn't black=
=20
>at 1500 nm. It's an organic dye. A shiny metal cone, stainless steel=20 >or something like that, and a carbon black-painted housing would work=20 >pretty well. > >Black copper oxide probably works OK in the IR too. > >Cheers > >Phil Hobbs
If you can get it, black chrome plating on copper ought to do pretty = well. Black chrome is a bunch of vertical chrome needles on the surface = (classic light trap). ?-) =20
On 11/12/2014 12:06 PM, John Larkin wrote:
> On Tue, 11 Nov 2014 20:53:19 -0800 (PST), "duedilligence@null.com" > <sroberts6328@gmail.com> wrote: > >> I should clarify, my bead attenuators use the small, clear, necklace beads with the hole in the center to provide scatter. These are not pure spheres, they are well suited to diffusion and scattering. >> >> The depth of the beads controls the attenuation. You may also crush the beads for greater attenuation per a given volume. Or add silica sand. >> >> When I use the bead scattering scheme with a window, I tilt the ghost beam into another dump. >> >> At 1-2 Watts CW this is very feasible. At higher powers professional discretion is advised and a safety case should be made. >> >> A good paper on Maximum Permissible Exposure calculations is here: >> http://safety.uchicago.edu/files/Laser%20MPE%20and%20NHZ%20Calculations.pdf >> >> Steve > > Sand packed in a metal tube might work, too. I could poke the probe > fiber in from the other end, until I get a reasonable signal level to > scope. > > There might be a few picoseconds of scattering, but that wouldn't be a > problem in the current application. >
The scatter is slower than you might think, unless the sand is a good absorber. It could easily be nanoseconds.
> The blackened copper tube would work similarly; poke in the fiber > until the coupling is good. Ebay sells liquid brass/copper blackening > stuff, and there's a great hardware store a couple of blocks away.
Make sure you test it in the IR, and at your power level. Cheers Phil Hobbs -- Dr Philip C D Hobbs Principal Consultant ElectroOptical Innovations LLC Optics, Electro-optics, Photonics, Analog Electronics 160 North State Road #203 Briarcliff Manor NY 10510 hobbs at electrooptical dot net http://electrooptical.net
On Thu, 13 Nov 2014 08:52:02 -0500, Phil Hobbs
<pcdhSpamMeSenseless@electrooptical.net> wrote:

>On 11/12/2014 12:06 PM, John Larkin wrote: >> On Tue, 11 Nov 2014 20:53:19 -0800 (PST), "duedilligence@null.com" >> <sroberts6328@gmail.com> wrote: >> >>> I should clarify, my bead attenuators use the small, clear, necklace beads with the hole in the center to provide scatter. These are not pure spheres, they are well suited to diffusion and scattering. >>> >>> The depth of the beads controls the attenuation. You may also crush the beads for greater attenuation per a given volume. Or add silica sand. >>> >>> When I use the bead scattering scheme with a window, I tilt the ghost beam into another dump. >>> >>> At 1-2 Watts CW this is very feasible. At higher powers professional discretion is advised and a safety case should be made. >>> >>> A good paper on Maximum Permissible Exposure calculations is here: >>> http://safety.uchicago.edu/files/Laser%20MPE%20and%20NHZ%20Calculations.pdf >>> >>> Steve >> >> Sand packed in a metal tube might work, too. I could poke the probe >> fiber in from the other end, until I get a reasonable signal level to >> scope. >> >> There might be a few picoseconds of scattering, but that wouldn't be a >> problem in the current application. >> > >The scatter is slower than you might think, unless the sand is a good >absorber. It could easily be nanoseconds.
Yikes. Yes, a couple of inches of sand in a tube could stretch a light pulse for nanoseconds. That would be fun to try some day. I'd better not use sand.
> >> The blackened copper tube would work similarly; poke in the fiber >> until the coupling is good. Ebay sells liquid brass/copper blackening >> stuff, and there's a great hardware store a couple of blocks away. > >Make sure you test it in the IR, and at your power level.
At a couple of watts, I probably can't get into big trouble. We have a grit blaster; I could scruff the inside of the tube first, then use the blackening stuff. Maybe curve the tube a little, and poke in the sampling fiber from the other end. -- John Larkin Highland Technology, Inc jlarkin att highlandtechnology dott com http://www.highlandtechnology.com
On 11/13/2014 10:26 AM, John Larkin wrote:
> On Thu, 13 Nov 2014 08:52:02 -0500, Phil Hobbs > <pcdhSpamMeSenseless@electrooptical.net> wrote: > >> On 11/12/2014 12:06 PM, John Larkin wrote: >>> On Tue, 11 Nov 2014 20:53:19 -0800 (PST), "duedilligence@null.com" >>> <sroberts6328@gmail.com> wrote: >>> >>>> I should clarify, my bead attenuators use the small, clear, necklace beads with the hole in the center to provide scatter. These are not pure spheres, they are well suited to diffusion and scattering. >>>> >>>> The depth of the beads controls the attenuation. You may also crush the beads for greater attenuation per a given volume. Or add silica sand. >>>> >>>> When I use the bead scattering scheme with a window, I tilt the ghost beam into another dump. >>>> >>>> At 1-2 Watts CW this is very feasible. At higher powers professional discretion is advised and a safety case should be made. >>>> >>>> A good paper on Maximum Permissible Exposure calculations is here: >>>> http://safety.uchicago.edu/files/Laser%20MPE%20and%20NHZ%20Calculations.pdf >>>> >>>> Steve >>> >>> Sand packed in a metal tube might work, too. I could poke the probe >>> fiber in from the other end, until I get a reasonable signal level to >>> scope. >>> >>> There might be a few picoseconds of scattering, but that wouldn't be a >>> problem in the current application. >>> >> >> The scatter is slower than you might think, unless the sand is a good >> absorber. It could easily be nanoseconds. > > Yikes. Yes, a couple of inches of sand in a tube could stretch a light > pulse for nanoseconds. That would be fun to try some day. > > I'd better not use sand. > > >> >>> The blackened copper tube would work similarly; poke in the fiber >>> until the coupling is good. Ebay sells liquid brass/copper blackening >>> stuff, and there's a great hardware store a couple of blocks away. >> >> Make sure you test it in the IR, and at your power level. > > At a couple of watts, I probably can't get into big trouble. > > We have a grit blaster; I could scruff the inside of the tube first, > then use the blackening stuff. Maybe curve the tube a little, and poke > in the sampling fiber from the other end. > >
Small integrating spheres are good for matching femtosecond pulses to the capacities of photodiodes. A typical 1-inch sphere will stretch any short pulse to roughly 3 ns. Cheers Phil Hobbs -- Dr Philip C D Hobbs Principal Consultant ElectroOptical Innovations LLC Optics, Electro-optics, Photonics, Analog Electronics 160 North State Road #203 Briarcliff Manor NY 10510 hobbs at electrooptical dot net http://electrooptical.net
On Thu, 13 Nov 2014 10:29:49 -0500, Phil Hobbs
<pcdhSpamMeSenseless@electrooptical.net> wrote:

>On 11/13/2014 10:26 AM, John Larkin wrote: >> On Thu, 13 Nov 2014 08:52:02 -0500, Phil Hobbs >> <pcdhSpamMeSenseless@electrooptical.net> wrote: >> >>> On 11/12/2014 12:06 PM, John Larkin wrote: >>>> On Tue, 11 Nov 2014 20:53:19 -0800 (PST), "duedilligence@null.com" >>>> <sroberts6328@gmail.com> wrote: >>>> >>>>> I should clarify, my bead attenuators use the small, clear, necklace beads with the hole in the center to provide scatter. These are not pure spheres, they are well suited to diffusion and scattering. >>>>> >>>>> The depth of the beads controls the attenuation. You may also crush the beads for greater attenuation per a given volume. Or add silica sand. >>>>> >>>>> When I use the bead scattering scheme with a window, I tilt the ghost beam into another dump. >>>>> >>>>> At 1-2 Watts CW this is very feasible. At higher powers professional discretion is advised and a safety case should be made. >>>>> >>>>> A good paper on Maximum Permissible Exposure calculations is here: >>>>> http://safety.uchicago.edu/files/Laser%20MPE%20and%20NHZ%20Calculations.pdf >>>>> >>>>> Steve >>>> >>>> Sand packed in a metal tube might work, too. I could poke the probe >>>> fiber in from the other end, until I get a reasonable signal level to >>>> scope. >>>> >>>> There might be a few picoseconds of scattering, but that wouldn't be a >>>> problem in the current application. >>>> >>> >>> The scatter is slower than you might think, unless the sand is a good >>> absorber. It could easily be nanoseconds. >> >> Yikes. Yes, a couple of inches of sand in a tube could stretch a light >> pulse for nanoseconds. That would be fun to try some day. >> >> I'd better not use sand. >> >> >>> >>>> The blackened copper tube would work similarly; poke in the fiber >>>> until the coupling is good. Ebay sells liquid brass/copper blackening >>>> stuff, and there's a great hardware store a couple of blocks away. >>> >>> Make sure you test it in the IR, and at your power level. >> >> At a couple of watts, I probably can't get into big trouble. >> >> We have a grit blaster; I could scruff the inside of the tube first, >> then use the blackening stuff. Maybe curve the tube a little, and poke >> in the sampling fiber from the other end. >> >> >Small integrating spheres are good for matching femtosecond pulses to >the capacities of photodiodes. A typical 1-inch sphere will stretch any >short pulse to roughly 3 ns. >
In our business, the speed of light is a real nuisance. -- John Larkin Highland Technology, Inc jlarkin att highlandtechnology dott com http://www.highlandtechnology.com
On Thursday, November 13, 2014 12:14:32 PM UTC-5, John Larkin wrote:
> On Thu, 13 Nov 2014 10:29:49 -0500, Phil Hobbs > <pcdhSpamMeSenseless@electrooptical.net> wrote: > > >On 11/13/2014 10:26 AM, John Larkin wrote: > >> On Thu, 13 Nov 2014 08:52:02 -0500, Phil Hobbs > >> <pcdhSpamMeSenseless@electrooptical.net> wrote: > >> > >>> On 11/12/2014 12:06 PM, John Larkin wrote: > >>>> On Tue, 11 Nov 2014 20:53:19 -0800 (PST), "duedilligence@null.com" > >>>> <sroberts6328@gmail.com> wrote: > >>>> > >>>>> I should clarify, my bead attenuators use the small, clear, necklace beads with the hole in the center to provide scatter. These are not pure spheres, they are well suited to diffusion and scattering. > >>>>> > >>>>> The depth of the beads controls the attenuation. You may also crush the beads for greater attenuation per a given volume. Or add silica sand. > >>>>> > >>>>> When I use the bead scattering scheme with a window, I tilt the ghost beam into another dump. > >>>>> > >>>>> At 1-2 Watts CW this is very feasible. At higher powers professional discretion is advised and a safety case should be made. > >>>>> > >>>>> A good paper on Maximum Permissible Exposure calculations is here: > >>>>> http://safety.uchicago.edu/files/Laser%20MPE%20and%20NHZ%20Calculations.pdf > >>>>> > >>>>> Steve > >>>> > >>>> Sand packed in a metal tube might work, too. I could poke the probe > >>>> fiber in from the other end, until I get a reasonable signal level to > >>>> scope. > >>>> > >>>> There might be a few picoseconds of scattering, but that wouldn't be a > >>>> problem in the current application. > >>>> > >>> > >>> The scatter is slower than you might think, unless the sand is a good > >>> absorber. It could easily be nanoseconds. > >> > >> Yikes. Yes, a couple of inches of sand in a tube could stretch a light > >> pulse for nanoseconds. That would be fun to try some day. > >> > >> I'd better not use sand. > >> > >> > >>> > >>>> The blackened copper tube would work similarly; poke in the fiber > >>>> until the coupling is good. Ebay sells liquid brass/copper blackening > >>>> stuff, and there's a great hardware store a couple of blocks away. > >>> > >>> Make sure you test it in the IR, and at your power level. > >> > >> At a couple of watts, I probably can't get into big trouble. > >> > >> We have a grit blaster; I could scruff the inside of the tube first, > >> then use the blackening stuff. Maybe curve the tube a little, and poke > >> in the sampling fiber from the other end. > >> > >> > >Small integrating spheres are good for matching femtosecond pulses to > >the capacities of photodiodes. A typical 1-inch sphere will stretch any > >short pulse to roughly 3 ns. > > > > In our business, the speed of light is a real nuisance.
Hmm would you like it to be faster or slower? (One of my favorite* questions on my qualifying exam was what would it be like if planks constant was an order of magnitude bigger and then smaller.) George H. * it's the only question I can remember.. the rest were boring math things mostly.
> > > -- > > John Larkin Highland Technology, Inc > > jlarkin att highlandtechnology dott com > http://www.highlandtechnology.com
On 11/11/2014 4:42 PM, Phil Hobbs wrote:
> On 11/11/2014 02:07 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? >> >> > > There are various kinds of beam dumps, some very efficient. With that > much power density, one popular beam dump is a stack of Gillette Blue > Blades, bolted together through the slot in the middle. Light has to > make several bounces off a dark-coloured surface before it can escape, > and it comes out at all sorts of angles. So something like that, > mounted inside a black metal box, might be a a good choice. I don't > know how good blue blades are at absorbing 1550 nm. > > http://tinyurl.com/l6ak9ny > > Another approach is to use a couple of pieces of black glass oriented at > Brewster's angle. The problem with that is the power density, so you > could expand the beam with a lens or curved mirror, and then absorb it. > > Krylon #1602 ultraflat black spray paint is a spectacularly good index > match to fused silica, so interestingly it's a much better absorber for > light coming in through the smooth glass/paint interface than through > the rough air/paint side. > > It's carbon-loaded, so it absorbs at all wavelengths, but I wouldn't > trust it at power densities over about 100-200 mW/cm**2 (i.e. a couple > of times zenith sunlight).
Turns out water absorbs at this wavelength pretty well. Construct a hollow block filled with water and two fiber ports, one for the light coming in and one for sampling the light. Put the sample port on an adjacent side to the incoming beam and recess it into a hole to minimize the chance of any light reaching the sample port in one bounce. With a couple of Watts coming in continuously it would only need to be a couple of inches on a side to dissipate the heat and not be overly warm. A cell phone dissipates that much power. Or you don't need to construct much at all... http://www.kenteklaserstore.com/trap-it-laser-beam-dumps.aspx -- Rick
In article <rtm46apkf59cidsbe0nfameggo6sclrein@4ax.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?
One classic approach is a curved piece of ordinary drawn copper tubing. The curve comes for free, as such tubing is sold at plumbing stores as a roll of tubing. Fire the beam straight into one open end, and the beam is forced to bounce around as it tries to follow the curve. Make the inside a shiny (not flat) black surface, so there will be little backscatter. Arrange things so the beam hits the walls at a slight angle - the specular reflections will be forward, and will hit the wall time after time. One can put a photodiode at the far end of the tube to detect what little gets through the beam dump, so you can tell that the beam is in fact entering the tube correctly. The scientific equivalent that I read in a pre-laser optics book is a curved horn (tapered tube with closed small end) made of hand-blown glass, coated on the outside with carbon black paint. Joe Gwinn