Warm outside, but getting several minute Duty cycle

BobMc said:

Now you got me really scratching my head. If the beam itself doesn't carry thermo energy. How come it doesn't matter ( within reason ) how far the laser is away from the thermo sensor of a LPM. I mean you can get a reading at 2" to 12" even more. So the energy would have to be in the beam itself. :thinking:

The 638nm is inherently weaker at the same power level as a 445nm because as far as I know the lower (smaller) the wavelength is the better burner it is. That's why a 1watt 405 is one of the best burner pre wattage there is. Please correct me if I'm mistaken? Thanks

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Honestly I'm open for anything, this was just a thought, I actually had no evidence to back it up I was just going off some random testing I did which could be way off, I was just wondering why red doesn't burn your skin at 500mw but 500mw blue or purple definitely does and very badly I may add even though I do understand short Vs. long wavelengths. I figured that if their was heat (thermal energy) in the beam than it should burn no matter what and that even somehow finding a way to put a thermometer in or very very close to the beam would actually read no heat at all? :thinking:
I honestly don't know. I'm actually 100% sure a lot of you all know more about that than I do
I guess I've been doing some pretty off the wall experiments lol

RedCowboy said:

You have more bandwidth, that is more wave fronts per given unit of measure with 405nm than 660nm, the number you know is the distance between waves, so like an impact hammer the 405 is running faster than the 660, the 405 is the higher frequency even though it's a lower number.

I calculated how many waves per second that is and it's a number with an exponent, just incredible.

Air consumes some energy, it's not like a vacuum, the beam you see is energy that won't get to the target.

On a foggy night or in heavy smoke a visible laser beam can be mostly consumed before it reaches even a close target 50 feet away.

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Ahh! Okay I see. I would say that definitely makes sense

paul1598419 said:

Actually, when talking about the power of a laser a watt is a watt, regardless of the wavelength, period. If you feel one over the other it is most likely because the two have very different profiles. The smaller the profile in the same power, the greater the energy density of the beam. This is independent of the wavelength.

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Jeez lasers can be Beautifully confusing, at least to me. lol I've only been a hobbyist for 2 years now.

BobMc said:

Thanks for the explanations. Does that mean that it is correct, that the shorter or lower wavelengths burn better because of that reason?

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Shorter wavelengths burn better for a couple reasons.

First, they can be focused to a smaller point given the same initial beam diameter and focusing optics.

Second, they tend to be absorbed better than longer wavelengths. At least as far as visible light goes.

High power density and better absorption means better burning.

As for a watt being a watt regardless of wavelength, Paul is correct. The energy of a photon at 650nm is lower than that of a 405nm photon, but 1W is still 1W, the 650nm laser just has to produce more photons than the 405nm laser in order to reach the same output power.

Richie89 said:

Honestly I'm open for anything, this was just a thought, I actually had no evidence to back it up I was just going off some random testing I did which could be way off, I was just wondering why red doesn't burn your skin at 500mw but 500mw blue or purple definitely does and very badly I may add even though I do understand short Vs. long wavelengths. I figured that if their was heat (thermal energy) in the beam than it should burn no matter what and that even somehow finding a way to put a thermometer in or very very close to the beam would actually read no heat at all?
I honestly don't know. I'm actually 100% sure a lot of you all know more about that than I do
I guess I've been doing some pretty off the wall experiments lol

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Your skin doesn't absorb red very well at all really, so most of the light is scattered through your skin/flesh or reflected off, meaning most of the power ends up going elsewhere. Green, blue and violet on the other hand are absorbed very well by skin/flesh so much more of the power is turned into heat.

Try burning green electrical tape with a green laser, and then with a red laser of equal power, the red will likely cut through it quicker as it is absorbed while the green is reflected off. That's why the tape appears green, it's absorbing red and blue light and reflecting green.

@Richie89; I am by no means a Laser Wizard, think your question. "What causes the heat in a laser beam" was a great one, have pondered it myself. Thanks for posing it. And a thanks to all the people that stepped up to answer.

If you are talking about shorter wavelengths burning better in the same power as longer wavelengths, then no they don't. And a 1+ watt red laser will burn your skin quite easily as long as the energy density of the beam is kept high by not allowing it to become large by comparison. The current 405nm laser diodes have a tight beam profile, while the current 635nm high power diodes have terrible divergence which will cause the energy density to be spread over a larger area at longer distances.

This is a great idea. Got any ideas about the actual lense thing?

diachi said:

Shorter wavelengths burn better for a couple reasons.

First, they can be focused to a smaller point given the same initial beam diameter and focusing optics.

Second, they tend to be absorbed better than longer wavelengths. At least as far as visible light goes.

High power density and better absorption means better burning.

As for a watt being a watt regardless of wavelength, Paul is correct. The energy of a photon at 650nm is lower than that of a 405nm photon, but 1W is still 1W, the 650nm laser just has to produce more photons than the 405nm laser in order to reach the same output power.




Your skin doesn't absorb red very well at all really, so most of the light is scattered through your skin/flesh or reflected off, meaning most of the power ends up going elsewhere. Green, blue and violet on the other hand are absorbed very well by skin/flesh so much more of the power is turned into heat.

Try burning green electrical tape with a green laser, and then with a red laser of equal power, the red will likely cut through it quicker as it is absorbed while the green is reflected off. That's why the tape appears green, it's absorbing red and blue light and reflecting green.

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Ahh I see, I've actually tried a couple of those things like you said and it definitely makes sense, and about that red laser thing, thanks for helping me out because that was always a head scratching moment, because when I first built that Mits500 I had a thought that if the wavelength was much longer than blue, than it shouldn't burn my hand, and so I stuck my hand in front of it not really knowing what would happen, so to my surprise it didn't burn at all. Even at 500apx MW so I tried to figure out how that was possible even understanding wavelengths, and of course I remembered that their was an awful lot of red light bouncing off my hand, so I figured it was in a way like "wasted energy" all that makes more sense to me now.

BobMc said:

@Richie89; I am by no means a Laser Wizard, think your question. "What causes the heat in a laser beam" was a great one, have pondered it myself. Thanks for posing it. And a thanks to all the people that stepped up to answer.

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Thanks Bob

paul1598419 said:

If you are talking about shorter wavelengths burning better in the same power as longer wavelengths, then no they don't. And a 1+ watt red laser will burn your skin quite easily as long as the energy density of the beam is kept high by not allowing it to become large by comparison. The current 405nm laser diodes have a tight beam profile, while the current 635nm high power diodes have terrible divergence which will cause the energy density to be spread over a larger area at longer distances.

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Yeah I can agree there for sure, these 638s are so damn horrible at Beam Divergence. What are they?
5mrad, 10mrad, or worse? I have no way to tell but I know they're absolutely horrible.

It confuses me sometimes because when I said that their is no Thermal energy in the beam, just energy in the beam in the form of certain wavelengths or radiation**
So when that beam touches something it causes the object that the beam is touching to then Heat up rapidly and burn, like when a red beam touches you and doesn't burn. I just watched an Ophir video that kinda said the same thing I was thinking. "A thermal Sensor that absorbs the light and converts it to heat to be read on the meter". But I'm not 100% sure what he meant. In a way I'm new to LPMs.

The part in the video is from 3:27-3:47

https://youtu.be/GsTmmVjLNsI

What you feel depends on how deep the laser penetrates into your skin and tissues below.

Red light actually passes through skin and tissues just below it, allowing blood circulation to take away a lot of the heat energy to temperature does not rise that much.

Green or blue light on the other hand is absorbed quickly under the skin surface and heats up locally, causing a painful hot spot and possibly a burn, even at equal power and power density compared to a red laser.

You can easily test this by shining a white flashlight through your fingers: the light that comes out is red, since part of the red light makes it all the way through wile the green and blue light does not.

Blood oxygenation meters that clip on your finger work by a similar principle: the have a red and an infrared led in them, and light meters on the other end. Those tell blood oxygen levels by looking at the ratio of how much of the red and IR makes it through your finger. This ratio depends on the ratio of oxygen-bound vs non-oxygen-bound heamoglobin in your red blood cells, bit the basic concept is similar.

As for the laser burn effect: this depends on skin color too - for white skin red light passes quite deeply, but it could cause pain or surface burns on black skin.

I rather doubt you would say that if you were hit up close with my 1+ watt 635nm laser. It will burn you quite easily I assure you.

Obviously, and it if it were a megawatt it'll burn a hole right through me.

This was not the point though, i said 'of equal power and power density'. So, for example a 200 mW laser with a beam diameter of 2mm: If that was 532 nm it'd painfully burn you very quickly, if it was 640 nm it would not.

Getting hit in the head with a cotton ball usually isn't painful either, but then again if you manage to speed it up to mach 10 it'll probably hurt quite badly, though still not -as badly- as marble of equal mass and speed.

That reminds me of the story of how the Challenger space shuttle crashed as many physicists wouldn't believe that a tile off the shuttle could punch a hole into it after becoming dislodged. There was one engineer who insisted that a tile could and did puncture the shuttle's under surface. Others claimed it would be like a piece of styrofoam hitting the windshield of a speeding car. Finally they did an experiment with a canon shooting a piece of tile at the metal surface.... and sure enough, it punctured the metal. It is always mass X velocity that equals force.

Richie89 said:

It's funny because I've been trying new ideas because I don't have large heat sinks.
I wanted to fire my laser directly straight up into the clouds and just sit there and admire it's beauty without worrying about rushing to shut it off every 45-60 sec. so I was thinking that if I could figure out how to keep that head/heatsink/module cool or around 45-55 degrees Fahrenheit than I'll triple my D cycle. So I threw a relatively small hand towel in the freezer making sure it was a tad damp and not soaked, let it near Freeze and wrap it around the head with a rubber band. I did this and went outside leaving it on for several minutes maybe 5 minutes and after turning it off I used my IR thermometer and found that the module was only sittin about 15 degrees hotter than usual. I doubt this same thing would work for a laser pushing over 3 amps and an output of over 4 watts, the one I used for this experiment was only a 1.2 watt 445.
Anyways I felt I had to share this with you all.

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Check my earlier post - idea for solution:

Radim said:

...


Outcome & tip - idea of solution to keep TEM00 for laserpainting purposes

Those experiments are leading me to idea of cooling them - best candidate is using cooling bags (you put them in freezer to cool them) and silicagel in some wrap. I discussed it before on LPF. I also considered many options of cooling, but I’m looking for something simple, versatile, reliable and fitting my needs.

Instead of neoprene I came with beta test using black paper and wrap foil and silicagel close to module. There will be cooling bag used in some zip back with air inside to insulate it a bit and have some kind of temperature regulation according to how much air is closed in the sack and creating layer of variable thickness. And this cooling wrap will cover temperature sensitive parts of the laser. In some cases even batt comparrment. This tied together with black rubber string. This would be laser prepared for laserpainting in these conditions. Even thermometer is considered, for tests. One of the questions is the positions of holes for buttons.

Once this idea is developed I could consider doing some advanced (e.g. neoprene) version. Should be very versatile for my needs.


I hope you enjoyed this wazup.

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Feel free to try and/or adjust this idea and for sure let us know how it worked, if you try it.


Edit:

RedCowboy said:

These commercial round finned sinks I buy and repurpose often have additional surface area multiplication in the form or little triangles that increase the length of the surface area because every bit of area is a heat vehicle to the surrounding air, there are also calculations as to fin spacing and what is most efficient for stationary air or moving air so it's easy to buy the ones made for stationary air use.

A larger heat sink finned or not is worth it if you enjoy runtime, it doesn't have to be huge, the hosts that eughmeus used to make from solid bar stock would be really nice.

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That is a very cool cooler. It brings me to idea of some attachable extrnal cooling to be fitted to laser head - kind of finned monster you posted, still there needs to be some thermal conductive fillings between external cooler and laser, which won't make laser dirty after removal (and also to accomodate various diameters of lasers). I believe even some fan could be added there to force air flow through the fins. Maybe even external TEC. Also nice alternative. But still it is depending on environment temperature - if too high, the idea with prefrozen cooling bags would be much better. Also they can be more insulated (with bubble wrap as cheap and versatile solution) from external environment to make sure they cool only laser and not that external environment.

GSS said:

I think you mean the Colombia disaster. Either way name or not they both were a horrible gruesome disaster that both had a chance to be avoided.
Like you mentioned they knew the shielding had been damaged and still chanced the re entry:thinking: and as everyone knew the O rings at cold temp didn't function that caused the Challenger's explosion:can:
What gives the power to the higher ups to give the go to on billions of dollars of spent money and people lives.:undecided:

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You're right. I have more than my share on senior moments. It was the Columbia.

paul1598419 said:

It is always mass X velocity that equals force.

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Or perhaps more that mass times velocity squared equals energy, depending on how the damage is incurred.

As for the Columbia disaster: not much could have been done about that really. They could have attempted to repair the heat shield but at risk of damaging it even further by accident, which is a sort of 50/50 if it goes as planned and worse if it doesnt.

They could not have reached the iss and used soyuz capsules to make their way down due to lack or propellant.

In retrospect they could have launched the atlantis shuttle, untested and unmanned, to serve as a rescue vehicle, although the crew would have to wait almost a month for it. They did have supplies to live off for that month though.

With 20/20 hindsight that is what they should have done, but then again, it could have re-entered with the crew surviving just as well. These are not tested situations and with only speculation and simulation to go on, i can't really fault the decision to try it.


The challenger disaster is far worse on error in judgement in my opinion: there was no urgency to launch at the planned date and time, and they could have waited for less cold conditions to launch just to err on the side of caution.

The aviation motto of 'taking off is always optional, landing usually is not' applies here.

If you have an aircraft with a known possible malfunction you can, and usually should, always abort taking off. If a malfunction developes in-flight you do not have the option not to land eventually since you will run out of fuel at some point. Airplanes sometimes land without extended landing gear if it malfunctions. Firefighters will be ready on the ground and all, but there is no way of avoiding that landing.

Benm said:

What you feel depends on how deep the laser penetrates into your skin and tissues below.

Red light actually passes through skin and tissues just below it, allowing blood circulation to take away a lot of the heat energy to temperature does not rise that much.

Green or blue light on the other hand is absorbed quickly under the skin surface and heats up locally, causing a painful hot spot and possibly a burn, even at equal power and power density compared to a red laser.

You can easily test this by shining a white flashlight through your fingers: the light that comes out is red, since part of the red light makes it all the way through wile the green and blue light does not.

Blood oxygenation meters that clip on your finger work by a similar principle: the have a red and an infrared led in them, and light meters on the other end. Those tell blood oxygen levels by looking at the ratio of how much of the red and IR makes it through your finger. This ratio depends on the ratio of oxygen-bound vs non-oxygen-bound heamoglobin in your red blood cells, bit the basic concept is similar.

As for the laser burn effect: this depends on skin color too - for white skin red light passes quite deeply, but it could cause pain or surface burns on black skin.

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I sure thanks for this info. I dunno why it bothered me so much that I couldn't fully understand this. Lol.

paul1598419 said:

I rather doubt you would say that if you were hit up close with my 1+ watt 635nm laser. It will burn you quite easily I assure you.

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:crackup: very true Paul, ugh! Must be nice having a 1+ watt 635. I have thought about building one with that output but I'm so scared to push a Non c mount that high, I guess it wouldn't be too crazy since everyone has done it. I assume 1.2amp max and a G2 would get me there if not than really close

You can push diodes that hard with some lifetime remaining on them.

The question is mostly why you would want to do so. On paper the difference between 800 mW and 1200 mW is a 50% increase in output power, and a meter will confirm this. The question is why you would actually want to do this. Obviously the 1200 mW would be brighter, probably notably so when used next to the 800 mW version.

But if you have either one of them they are both bloody bright. There is nothing magical about pusing a certain limit like '1 watt'. I usually run diodes quite a bit under their discoverd maximum power output to extend their lifetime.

In experimental setups i can understand the desire to get the maximum power for a diode, but if you are putting it into a practical product like a portable laser you could be a bit conservative on that: it's better to have a 800 mW pointer that lasts years of practical use compared to one that will fail in hours but provides 1200 mW.