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Thread: ~500nm laser wavelength material capabilitiies over CO2?

  1. #1

    ~500nm laser wavelength material capabilitiies over CO2?

    (Let me start by saying I'm not trying to cheap out and buy one of the scary ultra low cost lasers- I already have two CO2 lasers but run into material incompatibilities sometimes. I run my lasers partly for an engineering company that needs very unique materials cut frequently )

    Assuming I use the proper safety precautions for these lower wavelength, lower power lasers (in the 200mW-1000mW range) do they offer any particular material capabilities that CO2 lasers don't? As an example, I've needed to cut Kapton film for circuit masking in the past, and CO2 lasers just do a terrible job of it. There's tons of charring and heat damage.

    As I understand it the lower frequency lasers cut using a different physical interaction than the CO2 lasers, and I'm wondering if I can accomplish more things if I add a "cheap" visible light laser to my arsenal. There are dozens of 400-500nm laser modules available on eBay. With an actual safe enclosure, what additional materials could I expect to cut or mark with one of those lasers? I'm mainly interested in engineering plastics. PTFE cuts wonderfully with CO2, but PEEK and Kapton elude me.

  2. #2
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    Well I don't know anything about those, but as I had a roll of generic eBay Kapton tape I sacrificed a couple of inches to see if the fiber would cut it.
    200mm/s at 20kHz and minimum of 10 passes cut a circle out. Slight burn on edges, didn't distort the tape. I would think totally usable. Anything faster or higher frequency didn't cut.
    That's at 1061.2nm wavelength on the fiber.
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  3. #3
    You may have already seen this, but Universal has a resource article for Kapton:

    https://www.ulsinc.com/resources/adv...-center/kapton

  4. #4
    Interesting- it looks like the ULS lasers use a combo of 10.6 µm, 9.3 µm, and 1.06 µm beams to do their combo cutting. Apparently the 9.3 µm is good for Kapton (according to this thread- https://sawmillcreek.org/showthread....9-3-micron-CO2)

    According to this paper: http://www.spectralfringe.org/EDI/My...yImide1988.pdf the absorption just gets lower with lower frequencies. Extrapolating a bit makes it look like it's about 10% transmissive at ~1000 nm and about 1% transmissive at ~450 nm, and it gets less transmissive at lower frequencies still (so finding a 350 nm laser might be even best).

    Unfortunately that only shows part of the story, as I don't think absorptivity is the right measurement for this. As I understand it some of the low-frequency lasers cut material using a different physical phenomenon than thermal ablation.

  5. #5
    errruuugghhhh umm It's rather complex and there is no specific answer as a LOT of factors affect it

    Wavelength, Photon Energy, Material Absorption Coefficient, Pulse Energy, Emitted Power, Material Band Gap Energy are just a few of them. It's not even possible to make a direct comparison between two different wavelengths unless you use the rather abstract figure of Watt/Seconds and that's hit and miss at best (and only tells about 5% of the story)

    The effect you are thinking of PhotoThermal Vs PhotoChemical is a product of material band gap energy and photon energy, to get a photochemical effect in a CO2 cut you would need the material bandgap to be under 0.117eV (the photon energy of a normal CO2 laser beam) above that the effect is PhotoThermal and you cannot avoid carbonisation.

    If you drop to say a 445nm laser that has a Photon Energy of 2.788eV so any material with a bandgap under that figure will undergo a PhotoChemical process (assuming no material defects exist) and not suffer from carbonisation.

    NDFF (Neodymium-Doped Fluoride Fibre) will emit in the 380nm range but are both expensive and pretty much low power, if you want to get into the 157 - 351 range you would be looking at Excimer lasers to get anything like higher power (up to a few hundred watts) or Krypton - Ion or Argon - Ion if you want bench level test lasers. But before getting into all of that be advised you are looking at some pretty serious $$$$'s (quality labby lasers cost a LOT of money, figure on high end machine kinds of money just for the quality sources)

    UV lasers are typically used for manufacturing Fiber Bragg Gratings and refractive laser eye surgery.

    Also please be aware once you start hitting the UV wavelength the risks of skin cancer have been demonstrably proven over many years get down into the 10 - 121 nm range and you are playing with really nasty toys, Photon Energies in the 10 eV up to 124 eV photon energies (although absorbed by air quite well) and you are in the entirely ionising radiation range so about as dangerous as lasers get.

    As I understand it some of the low-frequency lasers cut material using a different physical phenomenon than thermal ablation.
    Just the opposite, frequency/wavelength follows the inverse proportionality law, high frequency = shorter wavelength hence the reason to get a 532nm laser you frequency double (second harmonic generation) a 1,064 nm such as an Nd-YAG

    Overall it's a really complex and exact science but with a LOT of possible variables that can change almost from second to second depending on so many factors

    ------------------------------

    Short version:

    Find out the BandGap energy of what you want to cut, find an affordable laser with a Photon Energy above the figure you have for the material
    You did what !

  6. #6
    Quote Originally Posted by Dave Sheldrake View Post
    errruuugghhhh umm It's rather complex and there is no specific answer as a LOT of factors affect it

    Wavelength, Photon Energy, Material Absorption Coefficient, Pulse Energy, Emitted Power, Material Band Gap Energy are just a few of them. It's not even possible to make a direct comparison between two different wavelengths unless you use the rather abstract figure of Watt/Seconds and that's hit and miss at best (and only tells about 5% of the story)

    The effect you are thinking of PhotoThermal Vs PhotoChemical is a product of material band gap energy and photon energy, to get a photochemical effect in a CO2 cut you would need the material bandgap to be under 0.117eV (the photon energy of a normal CO2 laser beam) above that the effect is PhotoThermal and you cannot avoid carbonisation.

    If you drop to say a 445nm laser that has a Photon Energy of 2.788eV so any material with a bandgap under that figure will undergo a PhotoChemical process (assuming no material defects exist) and not suffer from carbonisation.

    NDFF (Neodymium-Doped Fluoride Fibre) will emit in the 380nm range but are both expensive and pretty much low power, if you want to get into the 157 - 351 range you would be looking at Excimer lasers to get anything like higher power (up to a few hundred watts) or Krypton - Ion or Argon - Ion if you want bench level test lasers. But before getting into all of that be advised you are looking at some pretty serious $$$$'s (quality labby lasers cost a LOT of money, figure on high end machine kinds of money just for the quality sources)

    UV lasers are typically used for manufacturing Fiber Bragg Gratings and refractive laser eye surgery.

    Also please be aware once you start hitting the UV wavelength the risks of skin cancer have been demonstrably proven over many years get down into the 10 - 121 nm range and you are playing with really nasty toys, Photon Energies in the 10 eV up to 124 eV photon energies (although absorbed by air quite well) and you are in the entirely ionising radiation range so about as dangerous as lasers get.



    Just the opposite, frequency/wavelength follows the inverse proportionality law, high frequency = shorter wavelength hence the reason to get a 532nm laser you frequency double (second harmonic generation) a 1,064 nm such as an Nd-YAG

    Overall it's a really complex and exact science but with a LOT of possible variables that can change almost from second to second depending on so many factors

    ------------------------------

    Short version:

    Find out the BandGap energy of what you want to cut, find an affordable laser with a Photon Energy above the figure you have for the material
    Great post!

  7. #7
    Quote Originally Posted by Matt McCoy View Post
    Great post!
    Cheers Matt, it's really difficult to explain in reasonable terms without assuming a reader understands things that contribute to it. I try my best but sometimes it still comes out as incomprehensible babble
    You did what !

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