light leakage through loose threads, teflon tape

Black teflon tape?

The goopy pipe joint compound would probably work too. I'd guess there might be a lot of grazing incidence reflections spiraling in on the threads. So anything that scatters light might work.

ThorLabs should fix that.

--

John Larkin         Highland Technology, Inc 

lunatic fringe electronics

Probably not applicable here but it is cute so I wanted to pass it on. I recently I saw a little blurb in Chemical and Engineering News (weekly American Chemical Society news magazine) about researchers who needed an antireflective coating to block stray light in a "lab on a chip" they built up on microscope slides, with liquid flow channels, mixing chambers, and finally an analysis cell where they did laser fluorescence. After trying a variety of ideas they settled on matte black nail polish as the most effective and easiest to apply without damaging other chip layers. Not sure if this is behind a paywall or not, but see

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Regards, 
Carl Ijames

That's a favourite technique of George's. Normally black anodized threads aren't much of a problem--it takes many bounces off a black surface for the light to get into your detector.

Of course most black anodize is coloured with organic dyes, which aren't highly absorbing in the IR. You really want carbon for broadband loss.

How big was the leak, and what wavelength was it?

Cheers

Phil Hobbs

--
Dr Philip C D Hobbs 
Principal Consultant 
ElectroOptical Innovations LLC / Hobbs ElectroOptics 
Optics, Electro-optics, Photonics, Analog Electronics 
Briarcliff Manor NY 10510 

http://electrooptical.net 
http://hobbs-eo.com

Two quick-and-dirty, and two longterm/mass production thoughts.

Black paint (magic marker, usually) on the shiny metal bits or antiseize lubricant in the threads (graphite in grease - or petroleum jelly and penclil lead)

and

black-anodized aluminum threads (fine ones are good) oughtn't leak much or tapered threads (like pipe thread) never have to be loose - just turn until tight

Pipe threads for a two-inch tube aren't easy with hand tools, though I've got the taps and dies, but a real machine shop can do fine-pitch equivalents

The (thin) oxide on iron is ubiquitous, and a lot less transparent than Al2O3,

Well I use a single layer of teflon tape to take out the backlash in the fine threads of a thor lab lens tube. Not to block any light.

Not to you, but others. If you are blocking light to a silicon photodiode then one thing to be aware of is that something 'black' in the visible, may not be 'black' in the Near IR. (Which is one reason I like my incandescent bulb... lotsa NIR photons.)

I haven't done any sort of systematic study, but I find that black electrical tape makes a good light blocker at least down to 1 um.

George H.

Here there are 2 common grades, the gas grade is yellow which should work better than the white.

NT

How about Kapton tape. Its already fairly dark in the visible and is reported to have high emissivity in the far infra-red, so it might be quite black in the near infra red also.

John

Even thin Kapton tape is black at thermal wavelengths. I stick a bit onto shiny things to measure their temperature with our Flir.

--

John Larkin         Highland Technology, Inc 
picosecond timing   precision measurement  

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

Do you think it should be taped over 1210 resistors and SOT-23 transistors, for accurate readings? I'm setting T-max for part surface readings of 120 deg C. The circuit is working fine, but what about long-term reliability? I have 2 watts dissipated in three near- spaced 1210 resistors and three SOT-23 transistors.

Maybe could cover them with thermal tape or a heat- spreader, plus a heatsink, but what's the temp then?

--
 Thanks, 
    - Win

That doesn't sound bad. More copper helps a lot, since most parts dump their heat through their pads and leads. A 1210 is fine at 1 watt if it's soldered to some hunky copper pours.

The other things that work are to dab the part with a black whiteboard marker, or a bit of whiteout, or some Testor model paint.

The whiteboard marker is very thin so pretty well represents the part temperature.

Image a part and wave your hand around in a place that its "reflection" would bounce off the part into the imager. If the apparent temperature of the part doesn't change, its emissivity is high so its temperature indicates accurately. If it seems to reflect the heat from your hand, dab it with something.

Epoxy parts, like SOT23s, are pretty good.

Hey, here's a thermal image of a short under an FPGA, with a couple of amps injected. I think that was a ball-ball solder bridge.

--

John Larkin         Highland Technology, Inc 

lunatic fringe electronics

electrical tape seems to cut the brightness of LEDs by an aparrent factor of about 50 (mark-1 eyeball), metal tape is much more effective.

--
  When I tried casting out nines I made a hash of it.

I have larger solder pads, but all six parts are in close proximity. At 1kV, dissipating 2.1 watts they get to 115C, at 2.6 watts, they show 144C. That's at my 1.2kV goal, so add thermal tape and heatsinks, or scale back a bit on the performance.

--
 Thanks, 
    - Win

Eyeballs aren't calibrated. Incandescent lamp butted into photodiode

3 mA of current. (3 V at 1 k ohm)

1 layer black electrical tape (Scotch, Super 33+, professional grade.)

0.055 mV at 10 Meg ohm, but that's just the offset and doesn't change when the light is switched off.

A cheaper piece of electrical tape passed 0.5 V at 10 meg ohm ~50 nA... many orders of magnitdue! But the Scotch stuff is what I use.

George H.

That would explain why you're a natural at electronics

NT

I like to cool the backside of a hot spot on a PCB with a small gap-pad. That can really pull the temp down, and is still good HV insulation. One sq inch of decent pad, maybe 50 mils thick, would be well under 1 K/W.

Image the back of the board if you can. It may be a real hot spot.

Inner layer copper pours can spread heat too.

--

John Larkin         Highland Technology, Inc 

lunatic fringe electronics

The teflon tape worked. 5032nm.

--
 Thanks, 
    - Win

Plastic is pretty opaque in the mid-IR, so that's no big surprise. (Unless you meant 532 nm.)

Cheers

Phil Hobbs

--
Dr Philip C D Hobbs 
Principal Consultant 
ElectroOptical Innovations LLC / Hobbs ElectroOptics 
Optics, Electro-optics, Photonics, Analog Electronics 
Briarcliff Manor NY 10510 

http://electrooptical.net 
http://hobbs-eo.com

Yes, I misttyyppeedd! It was 532.

--
 Thanks, 
    - Win

Teflon tape is junk. It is an automatic leak. It is not code for gas lines or any of that shit though the assholes at the DIYs will try to tell you it is. Less diligent plumbers use it because it is less messy than pipe dope.

The main question here is how much pressure you are dealing with. If it is high then you might want to consider Locktite instead. I know it is not the EXACT purpose of the shit but then do we care what they wanted done with i t once they got their money ? Fukum.

If you are involved with the possibility of any big liability here I would do serious product testing before it goes out the door.

The problem with the pipe dope in your application is if the thing is glass or glass supported then unscrewing it may break it.

Just what I am saying. Not the expert on LASERs n shit at all but I have be en involved with some weird kinda processes. The guy to ask would have been the olman. he might have used like an alloy of maybe mercury and tin, to h ave it solid at operating temperatures but with a little Burnsomatic or may be even a pencil torch you could get it hot and take it back apart easily. but it has to not only well below the melting temperature, it also has to n ot cause too much thermal expansion or it might break or deform.

I am assuming right now that you have a reason for that tape. The way I see that is first of all that tape is white and quite translucent. Duct tape w ould be better as a light shield. however it has an aggressive adhesive so maybe not so good. Will masking tape take the heat ? (only if you are deali ng with any really pressure of course)