Static discharge using Lasers.

[B.B.Bubby]

A while ago I was taking temperature measurements of a fast moving paper web (paper rolls unwinding, going through an oven)
was just using one of those cheap laser IR temperature probes. This web was heavily static charged.

anyway I received a pretty decent static shock, and destroyed the sensor (i was around 2 meters away at the time). So I go off and buy a new ir probe and straight away same thing happened  :wtf
I cracked the sads after the second time and just made up the reading. It hurt too much and was getting expensive.

Obviously laser light can conduct electricity ?? 

It's got me thinking about making a static discharge device for industrial applications.
Maybe an array of laser diodes shining through a fine steel mesh (Earthed) then onto a static affected surface.


Has any one else come across this laser light phenomenon before? Any thoughts?

Cheers

[Ian.M]

Visible Laser light at power levels that do not cause atmospheric ionisation is just like ordinary light and does not make the atmosphere conductive.  It can however, also like ordinary light, stimulate photoemission of electrons from surfaces, though this effect is usually insignificant at atmospheric pressure.

To discharge charged surfaces, you'd need a high intensity short wavelength UV light source and unwanted ozone production would be a significant hazard.

I suspect the IR probe would have suffered the same damage if you'd stood in the same place with it switched off . . . .

[B.B.Bubby]

Visible Laser light at power levels that do not cause atmospheric ionisation is just like ordinary light and does not make the atmosphere conductive.  It can however, also like ordinary light, stimulate photoemission of electrons from surfaces, though this effect is usually insignificant at atmospheric pressure.

To discharge charged surfaces, you'd need a high intensity short wavelength UV light source and unwanted ozone production would be a significant hazard.

I suspect the IR probe would have suffered the same damage if you'd stood in the same place with it switched off . . . .

I received shocks both times as soon as the ir laser probe trigger was pulled. I was standing on a substantial steel walkway / bridge over the web at the time.

[Kalvin]

You have invented the basics for a laser printer. Anyway, I didn't imagine that the such a low power laser beam could create such a long conductive path in free air. Interesting, yet painful, discovery. 

High power lasers have been tested for triggering the lighting from the thunderclouds:
https://en.wikipedia.org/wiki/Lightning#Artificially_triggered
I suggest you should not try to measure the temperature of the thunderclouds.

[TerraHertz]

Maybe you were lucky it was paper, not plastic film. Have a read of this:
  http://amasci.com/weird/unusual/e-wall.html

That was in the early 1990s. Were there IR laser thermometers then? Anyway, they didn't try that.

[DanielS]

I received shocks both times as soon as the ir laser probe trigger was pulled. I was standing on a substantial steel walkway / bridge over the web at the time.

Your IR thermometer has a plastic body. Your own body is insulated from the walkway by your shoes' rubber soles while the thermometer's internals are insulated by its plastic housing. Your body charges up to a different electrostatic potential than the thermometer's innards from ambient static charge and when you pull the trigger, your fingers get close enough to an internal conductive surface for a spark to jump and equalize the voltage, zapping whatever else it finds in its path.

[LukeW]

For this sort of effect in a laser printer with infrared or visible light you need to have that light-sensitive semiconductor material on the drum, such as selenium.

This sort of static discharge is sometimes done using a radioactive source to create ionisation (like those StaticMaster brushes, etc) but it's also possible using a short-wavelength ultraviolet light, eg. from a UV laser.

If a plasma channel is opened in air with a UV laser, a whole lot of power can be dumped through it quickly.
https://en.wikipedia.org/wiki/Electrolaser

But the sort of phenomenon you're talking about probably can't happen, with most materials, with a visible or IR laser.

[TerraHertz]

This is only very faintly related, but I just came across it now, and it's cool:
google plasma wakefield acceleration

Where I read of it first:
http://www.smbc-comics.com/index.php?id=3780

[CatalinaWOW]

I received shocks both times as soon as the ir laser probe trigger was pulled. I was standing on a substantial steel walkway / bridge over the web at the time.

Your IR thermometer has a plastic body. Your own body is insulated from the walkway by your shoes' rubber soles while the thermometer's internals are insulated by its plastic housing. Your body charges up to a different electrostatic potential than the thermometer's innards from ambient static charge and when you pull the trigger, your fingers get close enough to an internal conductive surface for a spark to jump and equalize the voltage, zapping whatever else it finds in its path.

I agree, with the addition that you probably consciously or unconsciously extended the sensor toward the point you were measuring as you triggered the reading.  Most people seem to do this when using these probes.  I am sure it is nothing to do with the laser beam.  You could test that by just getting a cheap laser pointer with a conductive case (often sold in pet stores to amuse owners of cats and dogs) and pointing it at the paper rolls.

[Siwastaja]

You have invented the basics for a laser printer.

No, that's not how laser printer works.

Indeed, the surface of the drum has a static charge, which is locally removed by using a laser.

But the laser itself doesn't conduct; instead, the drum is coated with a light-sensitive material (traditionally, selenium; I don't know if they have come up with new materials) which starts to conduct when exposed to any light. The exposed parts conduct the static surface charge to the grounded drum itself. Before laser printers, traditional (analog) optical photocopiers simply projected the image to the drum by using a simple light source and lenses.


OP could easily just turn off the laser pointer feature, these IR temperature probes do not work by lasers by any means, although people always make that assumption. The laser pointer is there just to make aiming easier, and can be turned off (or if not, covered by tape).

[LaserSteve]

One, I've actually been in the room where the lasers pump a trial  accelerator similar to what is in that linked cartoon.

That said, get rid of the static by classical means.   The pulsed laser you need for air breakdown over a tiny path costs 55,000$ and up just for the laser.   That's not counting the means you need to have to sweep the beam back and forth etc.  You cannot do it with a continuous wave  laser, and it is hugely impractical to do it with a pulsed laser.  Reason being is the practical laser can only zap a cubic millimeter at most at one time. If you have really specialized optics, you might ionize a two cm long thin thread at best.  That's not going to help you clear a calendaring roll in a machine. Even if you scan the beam, you'd hit repetition rate issues with available lasers.

Conductive materials,  Antistatic Materials , changes in calendaring roller tribology, humidifiers, neutralized ion sources, pre-spaying an opposite charge, atmospheric pressure plasma machines etc ...

ALL of them work far, far far, far, far better then a laser induced breakdown for this task.

I do photonics for a living.  One of my concerns used to be air breakdown on the faces of glass optics and non-linear crystals.  I've sat and watched a tiny plasma ball form on my dead skin more then once. I know the mechanism quite well. This is not a cost effective means to use a nanosecond, picosecond, or femtosecond pulsed laser.

This is state of the art, made using several graduate students, probably upwards of 100,000 USD worth of technology, and several man-years of work. 

https://youtu.be/AoWi10YVmfE

It clearly would not cover a high speed calendaring roll.

Steve

[B.B.Bubby]

I received shocks both times as soon as the ir laser probe trigger was pulled. I was standing on a substantial steel walkway / bridge over the web at the time.

Your IR thermometer has a plastic body. Your own body is insulated from the walkway by your shoes' rubber soles while the thermometer's internals are insulated by its plastic housing. Your body charges up to a different electrostatic potential than the thermometer's innards from ambient static charge and when you pull the trigger, your fingers get close enough to an internal conductive surface for a spark to jump and equalize the voltage, zapping whatever else it finds in its path.

I agree, with the addition that you probably consciously or unconsciously extended the sensor toward the point you were measuring as you triggered the reading.  Most people seem to do this when using these probes.  I am sure it is nothing to do with the laser beam.  You could test that by just getting a cheap laser pointer with a conductive case (often sold in pet stores to amuse owners of cats and dogs) and pointing it at the paper rolls.

I'm certain the Laser did cause the discharge path. I did pretend to be Dirty harry whilst using it - but there was still a steel walkway between me and the web.

I've done some thinking and googling 

I don't think it was the actual paper web that was the source of the static discharge but more so its surrounding air.
The paper is dried by large gas fired ovens and low pressure high volume air in a very very dusty environment.

could have something to do with ionized air / dust and very low humidity?

Anyway - I know a few teachers, may be able to borrow a Van De Graaf generator, if so ill try to replicate the conditions at home and do the experiment.

Cheers

[LaserSteve]

You wont see static reduction with any laser you can hold in your hand. Period.

Steve

[Kalvin]

This clearly calls for documented re-run of the experiment. Just set up a few video cameras (or cell phones with full hd or otherwise good quality video cameras) to film the test from different angles when firing the laser. After that, let's analyze.

[Ian.M]

Video cameras in Faraday cages, otherwise the likely outcome is a big pile of dead electronics.  Also, its likely to be highly dependent on ambient humidity, so time of day and weather conditions will be important for reproducibility.

[LaserSteve]

And remember to run the test again and again, also with the laser in your hand but no beam emitted.

Trust me, there is no way a 5 mW red  or green laser aiming beam initiated a Townsend discharge or Leader Stroke in air to start a static discharge.

Steve

[B.B.Bubby]

And remember to run the test again and again, also with the laser in your hand but no beam emitted.

Trust me, there is no way a 5 mW red  or green laser aiming beam initiated a Townsend discharge or Leader Stroke in air to start a static discharge.

Steve

yeah but....       I still want to try 

was thinking about setting something like this up.

controlled room / chamber
an earthed laser mounted in an earthed Faraday cage / remotely triggered
air con on to dehumidify the air
portable gas stove on as a source of CO and any other combustion byproducts
the wifes hairdryer for some heat / maybe two of them
van de graaf generator
ion discharge device (can maybe get an AC generator from work + 1M bar) would like DC + / - but we don't use them.
A source of fine non explosive powder to float though the air ??
A metal halide lamp mounted from the ceiling


Would a neon globe in series with the lasers earth wire illuminate on a static discharge?

Cheers

[CatalinaWOW]

I'll have to temper my previous answer.  It is often through something weird like this that "new physics" are discovered.  So the experiment is welcome.  Just recognize that if you find something, it will be totally unexplained by current models of how a 5 mW red laser interacts with air and charge. 

[B.B.Bubby]

I'll have to temper my previous answer.  It is often through something weird like this that "new physics" are discovered.  So the experiment is welcome.  Just recognize that if you find something, it will be totally unexplained by current models of how a 5 mW red laser interacts with air and charge.

If we are talking about triggering events that are chain reaction-ish,  (https://en.wikipedia.org/wiki/Electron_avalanche) why does the power rating of the laser matter? isn't a photon a photon ie all photons of the same frequency have the same energy. It would only take one chance photon to trigger an event - just the chances are much less with a low power device?

[LaserSteve]

      The power level of the laser matters because it has to impart enough energy to overcome a high very  threshold. It then has to create a long enough stream of electrons and ions to sustain a conductive path. This has to stay  for a long enough time for the metal emitting the spark to achieve a very hot temperature in a very localized spot. Otherwise electrons will not "boil off" to sustain the discharge.   Arcs need a huge amount of free electrons in a very short time. This calls for either Field Emission, which needs a sharp, nano-sized metal point to emit from, or a enough current for a red hot Cathode Spot to form.

The Mean Free Path for a Red Photoelectron in air is less then 100 nanometers.  It simply cannot bridge the distance.

Nor could the 5 mW typical beam heat a localized spot of metal hot enough to initiate the arc emission.  Certainly not in Air. 

The red light is also unlikely to overcome the "Work Function" required to liberate copious free electrons from any metal surface that would not oxidize immediately in air. Your not talking about a  Sodium or Potassium photocathode material where red light could easily  knock off a P or S orbital electron. Your talking about a iron or aluminum metal where the outer orbital shells are tightly bonded, mostly filled,  and have very high bonding energy as they are far from the nucleus.  So its safe to assume very few photoelectrons are liberated.

If your aiming beam had any where near the legal maximum of 5 milliwatts for a class IIIA laser, that field would have been spread over a elliptical  spot size of probably two millimeters in diameter.  That fact, coupled with the fact that structural metals do not emit copious free electrons, ensured you never created a hot enough localized field to trigger an event. Period.

Laser triggered spark gaps are used, but they require very high peak power, Q-Switched, Pulsed, lasers to trigger.  They deliver the energy in about 7 nanoseconds, so the peak field strength is huge.  You simply do not have the high peak field from a red pointer.

I could do all the  math to prove this, but I simply do not have the half day required to document the problem and look up the equations, constants, and materials properties.

You observed a coincidence where you possibly squeezed the trigger right at the instant that a discharge was forming by other means.

 

Steve

[CatalinaWOW]

      The power level of the laser matters because it has to impart enough energy to overcome a high very  threshold. It then has to create a long enough stream of electrons and ions to sustain a conductive path. This has to stay  for a long enough time for the metal emitting the spark to achieve a very hot temperature in a very localized spot. Otherwise electrons will not "boil off" to sustain the discharge.   Arcs need a huge amount of free electrons in a very short time. This calls for either Field Emission, which needs a sharp, nano-sized metal point to emit from, or a enough current for a red hot Cathode Spot to form.

The Mean Free Path for a Red Photoelectron in air is less then 100 nanometers.  It simply cannot bridge the distance.

Nor could the 5 mW typical beam heat a localized spot of metal hot enough to initiate the arc emission.  Certainly not in Air. 

The red light is also unlikely to overcome the "Work Function" required to liberate copious free electrons from any metal surface that would not oxidize immediately in air. Your not talking about a  Sodium or Potassium photocathode material where red light could easily  knock off a P or S orbital electron. Your talking about a iron or aluminum metal where the outer orbital shells are tightly bonded, mostly filled,  and have very high bonding energy as they are far from the nucleus.  So its safe to assume very few photoelectrons are liberated.

If your aiming beam had any where near the legal maximum of 5 milliwatts for a class IIIA laser, that field would have been spread over a elliptical  spot size of probably two millimeters in diameter.  That fact, coupled with the fact that structural metals do not emit copious free electrons, ensured you never created a hot enough localized field to trigger an event. Period.

Laser triggered spark gaps are used, but they require very high peak power, Q-Switched, Pulsed, lasers to trigger.  They deliver the energy in about 7 nanoseconds, so the peak field strength is huge.  You simply do not have the high peak field from a red pointer.

I could do all the  math to prove this, but I simply do not have the half day required to document the problem and look up the equations, constants, and materials properties.

You observed a coincidence where you possibly squeezed the trigger right at the instant that a discharge was forming by other means.

 

Steve

When and if the experiment is duplicated, it will demonstrate that "something" is going on.  All of the above correctly describes why it is highly unlikely to involve the laser.  So, if the discharge can be repeatedly demonstrated you need to start doing things to isolate the true cause.  Since the OP believes it is the laser the tests should start with things to sort that out.  Simple things like moving the laser far away and coupling the beam to your test set up with mirrors.  If the power of the beam is a concern in this test just add power at the input.

Other obvious tests include turning the laser off and repeating.

And if, after extensive attempts to prove that nothing else is going on, and various methods to prove that the laser is indeed the triggering event, WOOHOO, you will set off a flood of people trying to figure out what is going on.  It might even prove to be important and lead to new technology applications, but even if real it is more likely to be a curiosity.

[B.B.Bubby]

Ok how about this as a theory as to what may have happened...   ( doing google research, cause i'm obsessed with this  )

We have a surface that is statically charged.

we have a gas region around this surface (boundary layer) - this gas is full of ionized air and byproducts of methane gas combustion
also in this gas are fumes from the ink drying process. Volatilized organic solvents. Precursors to organic semiconductors 

Organic semiconductors do shed electrons when exposed to low power visible light. + other weird stuff i do not understand.
https://en.wikipedia.org/wiki/Organic_semiconductor#Charge_transport_in_disordered_organic_semiconductors

maybe something like this is the air surrounding the ionized paper (released from the ink during drying)
https://en.wikipedia.org/wiki/Anthracene

also see here
https://en.wikipedia.org/wiki/Photochemistry

Cheers
Simon

[LaserSteve]

If you have hot, ionized, air, that greatly lowers the threshold for the arc to span a given distance. Especially if it has combustion products in it. Flames conduct electricity very well, as there is a readily available supply of free ions.   The laser  light did not cause the threshold event. Something ELSE did, such as ignition of a thin streamer of Methane.

Conversely if I have  methane around, in flammable concentrations,  I'm not going to be playing with high voltage, lasers, or other spark sources such as switch contacts arcing, even in low voltage circuits.  Fuel Air explosions are amazingly powerful and dangerous.  Not something you ever want to toy with in uncontrolled circumstances.

Once you've seen a  live FAE, you shudder at the thought of seeing another. They are highly efficient at creating energetic shockwaves.

Steve

[Ian.M]

There's also the paper dust issue.  Without any methane or solvent vapours, is still a serious explosion hazard: https://en.wikipedia.org/wiki/Dust_explosion

Maybe the answer is to install a large enough industrial humidifier to both cure the static problem and remove any risk of a dust explosion?

[wiss]

How can IR-lasers be used to measure temperature?