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Poor Man's Night Vision. You guess it. A flippin IR Laser, lmfao.

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MinnesotaStateUniversity

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I am in the process of building a night vision device. IIT's are quite expensive, so I was hoping to build an IR illuminator. However, instead of using IR throw LED's, I was hoping to use a single IR laser diode. The IR beam would then be sent through some type of lens (like a biconcave), & would be dispersed into a larger area. I've done a bit of research, but I'm still unsure on how to accurately calculate watts being diverted.

Below, is a "theory" on how to "accurately represent" watts being diverted. I believe this was linked from lucidscience off hackaday. I'm a bit skeptical & was hoping to clear some things up. Anyways, here it is:


"Assume I have a laser diode optical output of 1w, & a pupil size of .25" in my eye (@ Night). If I shined that 1W Laser directly into my eye, I will be blind instantly. However, what If I put that 1w through a lens & disperse it out into a circular area. I should only need to have a large enough circle so that the fraction that would go into my eyes is a safe amount, correct? Area of a Circle = Pi * (R)^2, So I can just figure the fraction of the pupil's area to the larger circle's area. I only need an "Eye-Safe Level," which I'll call 1mW. So I have (Diode Power) x (Pi * (.25")^2) / (Pi x r^2) which equals 1mW. Hence, 1000 x (1/16) / (r^2) = 1. Radius = about 8" or 16" in diameter. This means that If I have 1 watt of light, going through a lense , & spreading out into a 16" circle of light, and that shines directly into my Eye, my eye will see 1 milliwatt correct?"


^Math's correct, but isn't there a flaw behind the logic. From my understanding, when you use use a lens to disperse a laser, it is not the size of the lens, but rather the index (material), lenticular power (diopters), and the focal distance that gives you the dispersion equivalent. Therefore, in order to to calculate the dispersion factor, one would use a downstream vergence equation. However, this leads me to another question. It will not calculate watts being diverted. It calculates the dioptric equivalent. Instead of using Diopter, could I substitute with watts? So lets say I have 1W hitting a diverging lens, couldn't I determine that 16mW is at a point "x"mm behind the lens?

One last thing. Pupil aperture. A pupil is X distance from your retina. When a laser of 1W hits your retina, that's when one would go blind. I understand if I am going to disperse a beam, this aperture will come into play. This will block the already previously determined X factor depending on how fast the lens disperses the laser (dioptric power of the lens).



The character who wrote the theory used a diode out of a cd burner. I don't have the specs off hand, but I believe IR diodes out of burners rate around 250mW @ 900nm. Most high powered (150mW+) IR diodes have a fairly significant fast axiz, so the ouput will square. It looks like "area of a cirlce" is even more irrelevant.

One quick note: Assume I were to use a diode exceeding 150mW (multimode). How difficult would it be to utilize a diffusing filter, & eliminate all hot spots present throughout the nature of the beam profile? I know this is far from practical, but one way to get very even power distribution across the beam profile while at the same time circularizing the beam is to couple the output into a short piece of single-mode fiber and then use a lens to expand the fiber output. It took the guy 3 months to set up. Of course, he was dealing with a class 4a 1W laser, but is there an easier way, perhaps w/ a diode ranging from 150-250mW?
 

betwixt

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Personally, I would forget the idea and use standard IR LEDs.

The trouble with a laser is it needs very accurate current control, just a bit too much causes permanent failure. They also get quite hot and at 1W you would need a heat sink to keep it cool. Most laser diodes have a built-in sensor to monitor the light output and it has to be conected to a feedback loop to control the laser current, just passing current through it *might* work but any change, even a few degrees in temperature could kill it.

The other thing you should check is the IR wavelength, obviously our eyes can't see it directly so I'm assuming you are using a camera of some sort. Most CCD cameras have a built-in IR filter which prevents them seeing that part of the spectrum. You can buy ones wthout filters and in some cases you can remove the filter yourself but before getting too deeply involved, check the camera can actually see the laser at all.

I'm puzzled by your statement "a fairly significant fast axiz, so the ouput will square", (axiz = axis?) this sounds more like a statement about the optical pulse response rather than beam shape.

Brian.
 

keith1200rs

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I have to agree with Brian. Forget lasers. Your plan will probably result in eye damage/blindness. I do a fair bit of work with lasers and the work necessary to ensure they are eye safe is not trivial. Even with LEDs you need to spread the light about to avoid eye damage when they are infra red - hence the rings of LEDs you see rather than a single LED. The safe laser level for infra-red lasers is considerably less than 1mW - that only applies to visible lasers where the blink reflex is supposed to protect you.

Keith
 

MinnesotaStateUniversity

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Meh, anything exceeding 5mW can damaged your eyes. I'm very familiar w/ the dangers of class 4 lasers. Of course, this instrument will be used in a very secluded, private area & safetey glasses are a must.

I'm here to figure the mathematical equation to figure watts diverted. There has to be a way to calculate this.

I have a few wireless security cams laying around I'll be utilizing.



EDIT: Info found here: https://lucidscience.com/pro-laser night vision-1.aspx

^250mW & enough intensity to shoot out 200+ yrds. Not bad. However, his theory on diverted watts ...sucks, & that could result in an eye ball casualty lol
 
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tpetar

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MinnesotaStateUniversity

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I don't understand the link. Why hack a webcam only to remove it's IR filter when I can just use one of my security cam's on hand that already can pick up IR
 

tpetar

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Of course you can use one of your CCTV and solve problem.

You can get one very sensitive CCTV camera 0lux without IR LE diodes (very sensitive no need for illuminators, camera have just objective lens) and solve problem too.

Night-useful spectral range techniques can sense radiation that is invisible to a human observer. Standard web cam and video cameras are made for that human eye visible range, not infrared range. Lots of CCTV cameras, specially BW have capability to see good par of infrared range.

Infrared_spectrum.gif


https://www.hownightvisionworks.com/

https://en.wikipedia.org/wiki/Night_vision



Web camera can be modified to see and visualize radioactive Apha particles, but I dont want to bother you with that.
 
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