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optical question

Started by John Larkin November 11, 2014
On 11/14/2014 9:44 AM, Joe Gwinn wrote:
> 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 >
That's usually right, but not at 1-2 W. The paint will get toasted off where the first bounce occurs. The original Wood's horn was coated on the outside with lampblack (i.e. candle soot). Works great, but it's a bit messy. (R. W. Wood is another of my technical heroes--I forgot to put him in the last list I posted.) 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
In article <546618D9.40803@electrooptical.net>, Phil Hobbs
<pcdhSpamMeSenseless@electrooptical.net> wrote:

> On 11/14/2014 9:44 AM, Joe Gwinn wrote: > > 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 > > > > That's usually right, but not at 1-2 W. The paint will get toasted off > where the first bounce occurs.
I assume we are talking about the copper tube. I'll grant that paint could be overwhelmed if the beam is too small, but black chrome plating or the like should handle it. Or, just corrode the copper with sulfur fumes. My other approach is a bit of black iron gas pipe with both ends capped and an eccentric hole drilled in the wall. The beam passes through the offset hole, hits the inside of the far wall at about 30 degrees, and keeps on bouncing around the inside of the pipe. This is the blackbody source used in reverse.
> The original Wood's horn was coated on the outside with lampblack (i.e. > candle soot). Works great, but it's a bit messy. (R. W. Wood is > another of my technical heroes--I forgot to put him in the last list I > posted.)
I couldn't recall the name. Thanks. The books I read had dispensed with the soot and changed over to a soot-based black paint. Joe Gwinn
On 11/14/2014 12:49 PM, Joe Gwinn wrote:
> In article <546618D9.40803@electrooptical.net>, Phil Hobbs > <pcdhSpamMeSenseless@electrooptical.net> wrote: > >> On 11/14/2014 9:44 AM, Joe Gwinn wrote: >>> 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 >>> >> >> That's usually right, but not at 1-2 W. The paint will get toasted off >> where the first bounce occurs. > > I assume we are talking about the copper tube. I'll grant that paint > could be overwhelmed if the beam is too small, but black chrome plating > or the like should handle it. Or, just corrode the copper with sulfur > fumes. > > My other approach is a bit of black iron gas pipe with both ends capped > and an eccentric hole drilled in the wall. The beam passes through the > offset hole, hits the inside of the far wall at about 30 degrees, and > keeps on bouncing around the inside of the pipe. > > This is the blackbody source used in reverse. > > >> The original Wood's horn was coated on the outside with lampblack (i.e. >> candle soot). Works great, but it's a bit messy. (R. W. Wood is >> another of my technical heroes--I forgot to put him in the last list I >> posted.) > > I couldn't recall the name. Thanks. The books I read had dispensed > with the soot and changed over to a soot-based black paint. > > > Joe Gwinn >
Yup. My fave is Krylon #1602, as noted upthread. Works amazingly well on fused quartz. 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
In article <xY-dnfNdu5Jr2fvJnZ2dnUU7-U-dnZ2d@supernews.com>, Phil Hobbs
<pcdhSpamMeSenseless@electrooptical.net> wrote:

> On 11/14/2014 12:49 PM, Joe Gwinn wrote: > > In article <546618D9.40803@electrooptical.net>, Phil Hobbs > > <pcdhSpamMeSenseless@electrooptical.net> wrote: > > > >> On 11/14/2014 9:44 AM, Joe Gwinn wrote: > >>> 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 > >>> > >> > >> That's usually right, but not at 1-2 W. The paint will get toasted off > >> where the first bounce occurs. > > > > I assume we are talking about the copper tube. I'll grant that paint > > could be overwhelmed if the beam is too small, but black chrome plating > > or the like should handle it. Or, just corrode the copper with sulfur > > fumes. > > > > My other approach is a bit of black iron gas pipe with both ends capped > > and an eccentric hole drilled in the wall. The beam passes through the > > offset hole, hits the inside of the far wall at about 30 degrees, and > > keeps on bouncing around the inside of the pipe. > > > > This is the blackbody source used in reverse. > > > > > >> The original Wood's horn was coated on the outside with lampblack (i.e. > >> candle soot). Works great, but it's a bit messy. (R. W. Wood is > >> another of my technical heroes--I forgot to put him in the last list I > >> posted.) > > > > I couldn't recall the name. Thanks. The books I read had dispensed > > with the soot and changed over to a soot-based black paint. > > > > > > Joe Gwinn > > > > Yup. My fave is Krylon #1602, as noted upthread. Works amazingly well > on fused quartz.
I have always used 1602 too. One odd use - the top of the shelf below the windshield and above the dashboard, to cut down on reflections interfering with vision. Joe Gwinn
On Fri, 14 Nov 2014 16:00:58 -0500, Joe Gwinn <joegwinn@comcast.net>
Gave us:

>In article <xY-dnfNdu5Jr2fvJnZ2dnUU7-U-dnZ2d@supernews.com>, Phil Hobbs ><pcdhSpamMeSenseless@electrooptical.net> wrote:
>> > >> >> Yup. My fave is Krylon #1602, as noted upthread. Works amazingly well >> on fused quartz. > >I have always used 1602 too. One odd use - the top of the shelf below >the windshield and above the dashboard, to cut down on reflections >interfering with vision. > >Joe Gwinn
You must be a football player. :-) What about mil paints actually meant to be baked on and have high temp service applications? Those guys had decades to get to know what they were doing (the chem engineers making mil paints way back when).
In article <mirc6alooidf2o47bm138urlg6n2mam0gs@4ax.com>,
DecadentLinuxUserNumeroUno <DLU1@DecadentLinuxUser.org> wrote:

> On Fri, 14 Nov 2014 16:00:58 -0500, Joe Gwinn <joegwinn@comcast.net> > Gave us: > > >In article <xY-dnfNdu5Jr2fvJnZ2dnUU7-U-dnZ2d@supernews.com>, Phil Hobbs > ><pcdhSpamMeSenseless@electrooptical.net> wrote: > > >> > > >> > >> Yup. My fave is Krylon #1602, as noted upthread. Works amazingly well > >> on fused quartz. > > > >I have always used 1602 too. One odd use - the top of the shelf below > >the windshield and above the dashboard, to cut down on reflections > >interfering with vision. > > > >Joe Gwinn > > > You must be a football player. :-)
I think the intent is warpaint, not optics.
> What about mil paints actually meant to be baked on and have high temp > service applications?
The dashboard would melt.
> Those guys had decades to get to know what they were doing (the chem > engineers making mil paints way back when).
But it's a good point. There are high-temperature black paints intended for woodburning iron stoves (graphite and water-glass based?). I bet these paints wouldn't be bothered by a laser that small. There are also shiny black paints intended for gas grills and exhaust systems. Joe Gwinn
On 11/14/2014 4:39 PM, Joe Gwinn wrote:
> In article <mirc6alooidf2o47bm138urlg6n2mam0gs@4ax.com>, > DecadentLinuxUserNumeroUno <DLU1@DecadentLinuxUser.org> wrote: > >> On Fri, 14 Nov 2014 16:00:58 -0500, Joe Gwinn <joegwinn@comcast.net> >> Gave us: >> >>> In article <xY-dnfNdu5Jr2fvJnZ2dnUU7-U-dnZ2d@supernews.com>, Phil Hobbs >>> <pcdhSpamMeSenseless@electrooptical.net> wrote: >> >>>>> >>>> >>>> Yup. My fave is Krylon #1602, as noted upthread. Works amazingly well >>>> on fused quartz. >>> >>> I have always used 1602 too. One odd use - the top of the shelf below >>> the windshield and above the dashboard, to cut down on reflections >>> interfering with vision. >>> >>> Joe Gwinn >> >> >> You must be a football player. :-) > > I think the intent is warpaint, not optics. > > >> What about mil paints actually meant to be baked on and have high temp >> service applications? > > The dashboard would melt. > > >> Those guys had decades to get to know what they were doing (the chem >> engineers making mil paints way back when). > > But it's a good point. There are high-temperature black paints > intended for woodburning iron stoves (graphite and water-glass based?). > I bet these paints wouldn't be bothered by a laser that small. There > are also shiny black paints intended for gas grills and exhaust > systems.
Good point. I've never tried those. 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 Fri, 14 Nov 2014 16:39:30 -0500, Joe Gwinn <joegwinn@comcast.net>
Gave us:

>> You must be a football player. :-) > >I think the intent is warpaint, not optics.
I have always contended such and joke about it all the time. It is near impossible to 'catch glare' from those angles of incidence, and if you are that much like Tiger Woods, you probably are not cut out for the game. Yes... War Paint indeed. I laugh when someone denies it. Cough...
On Fri, 14 Nov 2014 16:39:30 -0500, Joe Gwinn <joegwinn@comcast.net>
Gave us:

>In article <mirc6alooidf2o47bm138urlg6n2mam0gs@4ax.com>, >DecadentLinuxUserNumeroUno <DLU1@DecadentLinuxUser.org> wrote: > >> On Fri, 14 Nov 2014 16:00:58 -0500, Joe Gwinn <joegwinn@comcast.net> >> Gave us: >> >> >In article <xY-dnfNdu5Jr2fvJnZ2dnUU7-U-dnZ2d@supernews.com>, Phil Hobbs >> ><pcdhSpamMeSenseless@electrooptical.net> wrote: >> >> >> > >> >> >> >> Yup. My fave is Krylon #1602, as noted upthread. Works amazingly well >> >> on fused quartz. >> > >> >I have always used 1602 too. One odd use - the top of the shelf below >> >the windshield and above the dashboard, to cut down on reflections >> >interfering with vision. >> > >> >Joe Gwinn >> >> >> You must be a football player. :-) > >I think the intent is warpaint, not optics. > > >> What about mil paints actually meant to be baked on and have high temp >> service applications? > >The dashboard would melt. > > >> Those guys had decades to get to know what they were doing (the chem >> engineers making mil paints way back when). > >But it's a good point. There are high-temperature black paints >intended for woodburning iron stoves (graphite and water-glass based?). >I bet these paints wouldn't be bothered by a laser that small. There >are also shiny black paints intended for gas grills and exhaust >systems. > > >Joe Gwinn
We mixed powdered silica into our potting to conduct heat better in HV applications. I'd bet that beads, and silica powder and an absorptive epoxy like stycast as a binder inside a sealed outer skin, might trap pretty good. Make the receiving "cup" just that. A (deep) cup shape with a parabolic end, of course... Or I guess a single pinpoint on a narrow stalk of a super-reflective media, and then those reflections get fed to the absorbing media. Instead of just a little added, like we were doing, one would flood the cup with beads and silica powder and barley have enough epoxy to bind it all together. Stycast can almost be peered though in thin enough cross section. Of course, I refer to human eye observations. Kind of like a bunch of hunting arrowheads together. Instead of razor blades, the points style would reduce any incidental reflection count to a very low number. I guess particulars of the beam which will be entering would weigh in.
Actually you want to minimize the sand if possible.  Adding any large amoun=
t of  epoxy causes far less scattering  as it more or less index matches th=
e glass.=20

I first saw the beads during a visit to the left coast as a Service Enginee=
r.

The graduate student who invented the hollow bead technique had up to 5 Jou=
le pulses attenuated by stacked "Tic-Tac" boxes in front of his photodiode =
detector. This was because his professor would not give him further budget =
for ND filters. He would add or remove boxes to change OD as needed. The sa=
me craft store had a wide variety of plastic boxes.

Necessity is often the mother of invention.

While I would not suggest his technique for day to day work, when you need =
a quick improvisation it works.=20


I left him a spare beam sampling wedge from my tool kit. That should have m=
ade his life a bit easier.

Steve