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Research Group Using Blue Diode Lasers to Fight COVID-19

Kyote

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I thought I would share these two press releases on the research I am currently working on. We are frequency doubling high-power blue laser diodes to create UV-C light that has been shown to inactivate viruses while being harmless to people. If you see the picture and the video you will clearly see the common diode package most here are familiar with, shout out to Jordan at DTR's Laser Shop for helping make this happen!

news.uci.edu/2020/05/19/uci-physicists-exploring-use-of-blu-ray-disc-lasers-to-kill-covid-19-other-viruses/

abc7.com/health/physicists-blu-ray-lasers-could-help-sterilize-covid-19/6200040/

(I tried to embed the link but sadly my post count is too low)
 



hoo7h

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Aha. The president was only a few wavelengths off I see ;)
Just kidding y'all! Let's not politicize this lol

Very interesting read, thank you for sharing
 

Kyote

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Haha, ya we aren't inserting this into bodies.

So basically UV-A and UV-B are harmful to us and are the components that cause sunburns, skin cancer, etc. However, once you get down to the UV-C band (which is approx around 220 nm) your dead skin cells or water in your eye absorb the light so efficiently that it is not harmful to you. We envision using this as a surface disinfectant or possibly to clean air passages in buildings or masks if it is portable enough.
 

Philipnzw

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How is the frequency doubling process achieved? Is the light still coherent laser light after the FD process? Would be sick to have a UV laser for us hobbyists.
 

Kyote

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What you need is a nonlinear crystal, basically think of the atoms of the crystal as masses attached by springs. The laser light can make those springs oscillate at the same frequency as the input light, but in certain crystals if the light has enough intensity you can have the mass-spring system oscillate at double or triple the input light frequency giving off light at the "second harmonic" or "third harmonic".

There are a variety of different nonlinear crystals. In fact the most common green laser pointer starts off in the infrared regime and is then frequency doubled into the green, it's a Nd:YVO4 laser that is frequency doubled using a KTP crystal. For UV you are probably going to want a crystal called BBO as it doesn't readily absorb in the UV. It is very hard to detect UV light so I caution anyone trying this out, but if your want to explore nonlinear optics just open up a green laser pointer!

Also, yes if things are managed properly the light is still coherent at the output.
 

Cyparagon

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My knee-jerk reaction is to lash out at you for suggesting that UVC is harmless to humans, but you get a break since you might be a researcher.

Your article states "everybody has to leave because in addition to UV-C, they make a lot of UV-A and UV-B, which can cause harm to humans." Tell me, why has no one thought of simply installing a UVC pass filter?

Your article also states "The issue is not whether you can make UV-C light. It’s whether you can fundamentally reduce the dollar-per-watt output of a device to a place that it becomes compelling to use UV-C light. " I'm having a bit of trouble finding specs on this, but one source says standard germicidal lamps are already ~40% efficient at producing UV. Maybe only half of that UV is germicidal, but you need to remember that a blu-ray diode is only ~20-25% efficient at best to begin with. Non-linear optics are not known for high conversion efficiency, but even if you get 100% conversion from your frequency doubling (which is an automatic nobel prize I think :) ), you BARELY beat a mercury germicidal tube in efficiency. But you forget the part where a germicidal tube is $10 or less. You think you can get a blu-ray diode, housing, optics, and SHG system for under $10? I don't see how this is even possible, my d00d.

It gets worse. If you're frequency-doubling 405nm, you're obviously down at 202.5nm. That's quite a bit from the peak effective wavelength for germicidal action. This means you're even more at a disadvantage because you're going to need a lot more 202nm light than 254nm light for equal effect.



Admittedly, there are very few native sources of light that produce UVC without UVB, but how do you explain the erythermal (sunburn) action spectrum? The standard erythema action spectrum provides an internationally accepted representation of the erythema-inducing effectiveness of wavelengths in the UV part of the spectrum.



This was developed by the CIE - the international commission on illumination - decades ago.

And since Sunburn is an inflammatory response in the tissue triggered by direct DNA damage by UV radiation, your claim that UVC is harmless goes against quite a mountain of data. If you've got good reason to believe the CIE is lying to all of us, you'd do the world more good by disproving this, instead of tinkering with lasers to create an inefficient light source.
 
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Gianakakis

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My knee-jerk reaction is to lash out at you for suggesting that UVC is harmless to humans, but you get a break since you might be a researcher.

Your article states "everybody has to leave because in addition to UV-C, they make a lot of UV-A and UV-B, which can cause harm to humans." Tell me, why has no one thought of simply installing a UVC pass filter?

Your article also states "The issue is not whether you can make UV-C light. It’s whether you can fundamentally reduce the dollar-per-watt output of a device to a place that it becomes compelling to use UV-C light. " I'm having a bit of trouble finding specs on this, but one source says standard germicidal lamps are already ~40% efficient at producing UV. Maybe only half of that UV is germicidal, but you need to remember that a blu-ray diode is only ~20-25% efficient at best to begin with. Non-linear optics are not known for high conversion efficiency, but even if you get 100% conversion from your frequency doubling (which is an automatic nobel prize I think :) ), you BARELY beat a mercury germicidal tube in efficiency. But you forget the part where a germicidal tube is $10 or less. You think you can get a blu-ray diode, housing, optics, and SHG system for under $10? I don't see how this is even possible, my d00d.

It gets worse. If you're frequency-doubling 405nm, you're obviously down at 202.5nm. That's quite a bit from the peak effective wavelength for germicidal action. This means you're even more at a disadvantage because you're going to need a lot more 202nm light than 254nm light for equal effect.



Admittedly, there are very few native sources of light that produce UVC without UVB, but how do you explain the erythermal (sunburn) action spectrum? The standard erythema action spectrum provides an internationally accepted representation of the erythema-inducing effectiveness of wavelengths in the UV part of the spectrum.



This was developed by the CIE - the international commission on illumination - decades ago.

And since Sunburn is an inflammatory response in the tissue triggered by direct DNA damage by UV radiation, your claim that UVC is harmless goes against quite a mountain of data. If you've got good reason to believe the CIE is lying to all of us, you'd do the world more good by disproving this, instead of tinkering with lasers to create an inefficient light source.
Well said. Also I would like to see the aforementioned crystal that can directly double blue into UVC for under 1k.
 

Kyote

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Cyparagon you raise some good points, and too be honest I am not super optimistic in the outcome of this project. We are mainly taking this on because there has been a university wide hold on any "non-essential" research, and by doing this we at least get to get into the lab and characterize some diodes that we wanted to do anyhow. The main reason for posting this was more to show people here how a common diode package is being used in research and got some media attention.

First, if this ends up being something worthwhile we almost certainly won't be using the BDR-209 due to conversion efficiency reasons, but hey the media likes the talking point of using Blu Ray players to disinfect and it is one of the easier ways to explain the concept to people. The power costs to run either of these are pretty minimal so it really comes down to the cost of the assembly, and you are right there is absolutely no way you're getting this package down to the price point of $10 and it will even be difficult to hit the price point of a germicidal lamp assembly.

However, it's really less about the total wattage emitted but rather the delivered spot intensity in W/area. Here a laser based UV source can shine since it can be tightly focused making its power output more effective at the target. We have a couple schemes in mind on how to do this but it is not something that I can discuss at this time.

On the point about UV damage to skin and eyes, the CIE website states "The problem of dosimetry in skin photobiology lies in the fact that the ability of ultraviolet (UV) radiation to elicit erythema in human skin depends strongly on wavelength, encompassing a range of four orders of magnitude between 250 nm and 400 nm" while the Wikipedia article mentions that "The skin and eyes are most sensitive to damage by UV at 265–275 nm wavelength"

There are a few studies looking at the UV-C band effect on skin that find it to be less damaging to synthetic skin than 254 nm UV-B light
Screen Shot 2020-05-23 at 12.51.38 PM.png
Screen Shot 2020-05-23 at 12.53.09 PM.png

Regarding the germicidal effectiveness of UV-C light compared to the standard 254 nm, I'm pretty sure that the chart posted extrapolates the germicidal effectiveness into the UV-C. Here is a chart from a study it may be based off of,
Screen Shot 2020-05-23 at 1.00.16 PM.png

Since the germicidal process from UV light is primarily from DNA/RNA destruction, the absorption spectrum of the different amino acids suggests that this trend could reverse around 230 nm,
Screen Shot 2020-05-23 at 1.07.15 PM.png

and could explain these following studies looking at killing MRSA with UV light. A surface is considered 'disinfected' if you can kill Log 2 of the virus/bacteria,
Screen Shot 2020-05-23 at 1.09.14 PM.png
Screen Shot 2020-05-23 at 1.10.30 PM.png
 

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Shmackitup

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Have you considered trying the Sharp GH04W10A2GC diodes? They can reach output powers upwards of 2 watts.
 

Snecho

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I really like this kind of stuff because way back when, I won best idea in this youth robotics/inventing thing where the theme was farming and keeping food safe.

My idea was a 360° UV rotating refrigerator/chamber/trailer for keeping food fresh.
 

jors

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Why not 450nm for SHG? But I can't imagine how you could get SHG phase matching from a M2>5 MM blue TO Can diode. Moreover peak WL is going to change depending of current and temp, but also, from one diode to another.
 

Cyparagon

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SHG is often a lot easier (especially with experimental/theoretical crystal options) with a single mode pump. Violet single mode limit is a lot higher in practice than blue.

If wavelength variation is a problem, that's what thermal regulation is for.
 

jors

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SHG is often a lot easier (especially with experimental/theoretical crystal options) with a single mode pump. Violet single mode limit is a lot higher in practice than blue.

If wavelength variation is a problem, that's what thermal regulation is for.
Yes, ok, but these bluray diodes are multimode. Even if you get stable WL this is not a narrow band so I don't expect any coherent emission with SHG. Maybe 1-2mW of UV if lucky for a 1,5W 405nm? So if you need cooling control for just couple mW UV (or maybe nothing) I can't see the benefits for SHG on blueray diodes... I've only seen acceptable conversion from Single Mode external cavity tapered diodes..
 




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