Night Vision Eye damage from reflection of 3B IR laser

[icedragonmx]

If I was lighting up steel plates and coke cans at distances from 25-500+yards, what worries do I have with regards to a reflection from a Class 3b 810nm IR beam, 90mW at 0.1 to 5 degrees zoom. Any worries about tall grass etc from the prone at 0 yards? Not going to be looking at the beam but how much care is required for some weekend fun in the dark?

 

[BOLTRIPPER]

Re: Eye damage from reflection of 3B IR laser

should'nt you be in hockey league

 

[Wardy]

Re: Eye damage from reflection of 3B IR laser

Huh?

 

[icedragonmx]

Re: Eye damage from reflection of 3B IR laser

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: BOLTRIPPER</div><div class="ubbcode-body">should'nt you be in hockey league </div></div>

To fat for that

Just worried about a strong reflection from a 3B laser- yes/no on that concern?

 

[Captain Moroni]

Re: Eye damage from reflection of 3B IR laser

So let me get this strait Canadians cant have more than a 5 round mag but you can have high powered lasers?

 

[shankster..]

Re: Eye damage from reflection of 3B IR laser

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: Captain Moroni</div><div class="ubbcode-body">So let me get this strait Canadians cant have more than a 5 round mag but you can have high powered lasers? </div></div>

 

[icedragonmx]

Re: Eye damage from reflection of 3B IR laser

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: Captain Moroni</div><div class="ubbcode-body">So let me get this strait Canadians cant have more than a 5 round mag but you can have high powered lasers? </div></div>

Don't worry, I don't have any sharks to strap it on. Would hope I could hit something with 5 tries too. The max I have is 500mw but no real limit here for lasers or NV. The US just won't export anything interesting that was made in the US. I can even let a pal from the US look through my NV

Was just wondering if 90mw is too strong if reflected back by the grass or steel etc.

Shankster- Thanks for the laugh!

 

[IR-V]

Re: Eye damage from reflection of 3B IR laser

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: icedragonmx</div><div class="ubbcode-body">If I was lighting up steel plates and coke cans at distances from 25-500+yards, what worries do I have with regards to a reflection from a Class 3b 810nm IR beam, 90mW at 0.1 to 5 degrees zoom. Any worries about tall grass etc from the prone at 0 yards? Not going to be looking at the beam but how much care is required for some weekend fun in the dark? </div></div>

What you are seeking to know is "Nominal Ocular Hazard Distance (NOHD)". NOHD is the distance from a laser emission source where eye damage will occur from even momentary exposure. The formula is as follows:

<span style="font-weight: bold">NOHD in feet = (32.8/mR)*SQRT(0.5*mW)</span>

mR = laser beam divergence in milliradians (1 deg = 17.45 mR)
mW = laser output in milliwatts

For your laser variables set to the narrowest beam, the NOHD is 126 feet (42 yards). Reflective surfaces such as mirrors and polished metal surfaces will reflect close to 100% of the laser radiation. That means highly reflective objects within half the NOHD distance (21 yards) from your laser emitter on narrow focus will reflect enough radiation to injure your eyes.

Live vegetation is highly reflective to infrared (IR) radiation. Laser radiation is much more focussed than light coming from a light bulb, therefore the attenuation formulas for 360 degree radiation sources, such as the Inverse Square Law, are not a best fit for understanding the proprerties of laser radiation. The more relevant Gaussian Beam calculations are much too complicated and time consuming for this thread. Therefore, for layman use, it is best to assume all objects within the laser's NOHD to be almost perfectly reflective, and to protect accordingly.

So, for your 90 mW IR laser set to .1 degree divergence, protect your eyes from anything reflecting laser radiation back toward you within the zone up to 21 yards away from your laser emitter.

IR-V

 

[cj7hawk]

Re: Eye damage from reflection of 3B IR laser

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: IR-V</div><div class="ubbcode-body"> What you are seeking to know is "Nominal Ocular Hazard Distance (NOHD)".
</div></div>

Excellent post !

Thankyou

David

 

[shankster..]

Re: Eye damage from reflection of 3B IR laser

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: IR-V</div><div class="ubbcode-body"><div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: icedragonmx</div><div class="ubbcode-body">If I was lighting up steel plates and coke cans at distances from 25-500+yards, what worries do I have with regards to a reflection from a Class 3b 810nm IR beam, 90mW at 0.1 to 5 degrees zoom. Any worries about tall grass etc from the prone at 0 yards? Not going to be looking at the beam but how much care is required for some weekend fun in the dark? </div></div>

What you are seeking to know is "Nominal Ocular Hazard Distance (NOHD)". NOHD is the distance from a laser emission source where eye damage will occur from even momentary exposure. The formula is as follows:

<span style="font-weight: bold">NOHD in feet = (32.8/mR)*SQRT(0.5*mW)</span>

mR = laser beam divergence in milliradians (1 deg = 17.45 mR)
mW = laser output in milliwatts

For your laser variables set to the narrowest beam, the NOHD is 126 feet (42 yards). Reflective surfaces such as mirrors and polished metal surfaces will reflect close to 100% of the laser radiation. That means highly reflective objects within half the NOHD distance (21 yards) from your laser emitter on narrow focus will reflect enough radiation to injure your eyes.

Live vegetation is highly reflective to infrared (IR) radiation. Laser radiation is much more focussed than light coming from a light bulb, therefore the attenuation formulas for 360 degree radiation sources, such as the Inverse Square Law, are not a best fit for understanding the proprerties of laser radiation. The more relevant Gaussian Beam calculations are much too complicated and time consuming for this thread. Therefore, for layman use, it is best to assume all objects within the laser's NOHD to be almost perfectly reflective, and to protect accordingly.

So, for your 90 mW IR laser set to .1 degree divergence, protect your eyes from anything reflecting laser radiation back toward you within the zone up to 21 yards away from your laser emitter.

IR-V
</div></div>

Wow IR-V, this is a great post. Thanks for the contribution.

 

[FCS]

Re: Eye damage from reflection of 3B IR laser

Using any kind of collective optics (rifle scope, binoculars, etc?) while lighting up targets? If so then you'll need to factor that in also.

I didn't see that in the nominal hazard calcualation.

NV will most probably have a PMT so no direct optical path to the eye, will burn your screen though with a specular reflection.

"Not looking at beam", how exactly do you know this? After 20+ years of working with high powered laser systems I'll tell you this, even in a laboratory setting you get stray reflections. Field use, pointing beam in an "uncontrolled" enviroment you'll have reflections you haven't even though of.

Catch a concave surface and get a focused reflection back....

90mW @ 810nm is more then enough to burn retina, get yourself some good laser safety glasses, min OD of 5 for 810nm. You get exactly one set of eyes and I'm not aware of any replacement parts for the retina yet.

 

[Chanonry]

Re: Eye damage from reflection of 3B IR laser

IR-V excellent post. I just learned not to mess with that shit...

 

[IR-V]

Re: Eye damage from reflection of 3B IR laser

<div class="ubbcode-block"><div class="ubbcode-header">Quote:</div><div class="ubbcode-body">

Wow IR-V, this is a great post. Thanks for the contribution. </div></div>

Thanks for appreciating, Shankster. Really glad to be able to share info with you, and help support eye safety for all the good brothers that visit here.

IR-V

 

[IR-V]

Re: Eye damage from reflection of 3B IR laser

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: Chanonry</div><div class="ubbcode-body">IR-V excellent post. I just learned not to mess with that shit... </div></div>

You're welcome, Chanonry -- thanks for appreciating. I hope you will not be discouraged from exploring the utility of Class 1 / eye-safe IR laser technologies.

IR-V

 

[IR-V]

Re: Eye damage from reflection of 3B IR laser

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: cj7hawk</div><div class="ubbcode-body"> Excellent post !

Thankyou

David </div></div>

You're welcome, David. I also enjoy and appreciate all the excellent knowledge you share here.

IR-V

 

[icedragonmx]

Re: Eye damage from reflection of 3B IR laser

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: IR-V</div><div class="ubbcode-body"><div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: icedragonmx</div><div class="ubbcode-body">If I was lighting up steel plates and coke cans at distances from 25-500+yards, what worries do I have with regards to a reflection from a Class 3b 810nm IR beam, 90mW at 0.1 to 5 degrees zoom. Any worries about tall grass etc from the prone at 0 yards? Not going to be looking at the beam but how much care is required for some weekend fun in the dark? </div></div>

What you are seeking to know is "Nominal Ocular Hazard Distance (NOHD)". NOHD is the distance from a laser emission source where eye damage will occur from even momentary exposure. The formula is as follows:

<span style="font-weight: bold">NOHD in feet = (32.8/mR)*SQRT(0.5*mW)</span>

mR = laser beam divergence in milliradians (1 deg = 17.45 mR)
mW = laser output in milliwatts

For your laser variables set to the narrowest beam, the NOHD is 126 feet (42 yards). Reflective surfaces such as mirrors and polished metal surfaces will reflect close to 100% of the laser radiation. That means highly reflective objects within half the NOHD distance (21 yards) from your laser emitter on narrow focus will reflect enough radiation to injure your eyes.

Live vegetation is highly reflective to infrared (IR) radiation. Laser radiation is much more focussed than light coming from a light bulb, therefore the attenuation formulas for 360 degree radiation sources, such as the Inverse Square Law, are not a best fit for understanding the proprerties of laser radiation. The more relevant Gaussian Beam calculations are much too complicated and time consuming for this thread. Therefore, for layman use, it is best to assume all objects within the laser's NOHD to be almost perfectly reflective, and to protect accordingly.

So, for your 90 mW IR laser set to .1 degree divergence, protect your eyes from anything reflecting laser radiation back toward you within the zone up to 21 yards away from your laser emitter.

IR-V
</div></div>

Thank you very much IR-V! I will be doing some research on this before I start. I do appreciate you taking the time to give such a well informed response to my questions. Thanks!

 

[icedragonmx]

Re: Eye damage from reflection of 3B IR laser

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: McCourt Munitions LLC</div><div class="ubbcode-body">Using any kind of collective optics (rifle scope, binoculars, etc?) while lighting up targets? If so then you'll need to factor that in also.

I didn't see that in the nominal hazard calcualation.

NV will most probably have a PMT so no direct optical path to the eye, will burn your screen though with a specular reflection.

"Not looking at beam", how exactly do you know this? After 20+ years of working with high powered laser systems I'll tell you this, even in a laboratory setting you get stray reflections. Field use, pointing beam in an "uncontrolled" enviroment you'll have reflections you haven't even though of.

Catch a concave surface and get a focused reflection back....

90mW @ 810nm is more then enough to burn retina, get yourself some good laser safety glasses, min OD of 5 for 810nm. You get exactly one set of eyes and I'm not aware of any replacement parts for the retina yet.

</div></div>

Thanks! Will be getting a pair of safety glasses prior to starting. Nevermind the grass etc the snow coming down right now would be a big concern too. "uncontrolled enviroment" is a given!

 

[george etter]

Re: Eye damage from reflection of 3B IR laser



CJ-7 hawk & IR-v many thanxs to the both of you ! McCourt munitions could you or for that matter all of you speak a bit about eye safety equipment.Would be quite a treat for my eager ears

atb george

 

[IR-V]

Re: Eye damage from reflection of 3B IR laser

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: stuhlschuter</div><div class="ubbcode-body">

CJ-7 hawk & IR-v many thanxs to the both of you ! McCourt munitions could you or for that matter all of you speak a bit about eye safety equipment.Would be quite a treat for my eager ears

atb george </div></div>

Sure can, Stuhlschuter!

Optical Density (OD) pertains to a filter's ability to attenuate the intensity of light at a certain wavelength or range of wavelengths. An OD rating of "1" would reduce the intensity by a factor of 10 (ten to the power of 1), while and OD rating of "5" would reduce the intensity by a factor of 100,000 (ten to the power of 5).

To give a margin of safety, it is best to use a filter (to protect your eyes) with an OD rating at least a couple factor levels beyond the output level of your laser emission device, and with a sustained OD for a range of wavelengths below and above the "target" wavelength for your device.

For example, with an IZLID 1000, which emits 990-1000 mW @ 860 nanometers wavelength, an OD 3 filter (-10^3, or -1000) is right at the threshhold of full attenuation. However, an OD 5 filter (-10^5, or -10000) gives extra, high assurance of full attenuation. When protecting your eyes while operating high powered lasers, there is no such thing as "too much protection." This is especially true because the published output levels and output wavelengths for laser devices is typically a *nominal* rating, and actual outputs, when measured with laboratory equipment, will commonly show variances to the published ratings within an "acceptable" range of deviation.

Some examples, from a wavelength perspective:

DBAL: 810-840 nm
ATPIAL: 830 nm
GCP-2B: 810-860 nm
IZLID 1000: 860 nm
MPLI: 820-845 nm

Thus, most IR laser devices emit within a wavelength range between 810 - 860 nm.

My preferred source for safety glasses for use with IR lasers is www.cascadelaser.com. Their "IRD5" filter provides OD 5 attenuation from 800 - 1790 nm, and provides OD 3 and 4 attenuation in the wavelengths above and below the wavelengths where the filtering is at its peak strength (or 'optical density').

Furthermore, the "IRD5" filter maintains pretty decent *visible* light transmission (VLT) with approx. 16% attenuation -- this means that you're not stumbling around like a blind man in visible light when you're wearing the protective filter; and it will not block out too much of the visible light from the viewing (ocular) end of your night vision device.

There's a variety of frame styles to pick from. While a wrap-around lens and translucent side lenses are available, I opt for the ones with temple pieces and which are shuttered on the sides with opaque (non-translucent) frame material. These are lighter weight than goggles but still seal around the face well; will fit well over prescription eyeglass lenses; and yet stay close enough to the face so as to not interfere with night vision goggles at the same time.

As with all protective equipment, always perform diagnostic tests to validate for proper function at routine intervals. You can do this by placing one of the filter lenses over the objective lens of a night vision monocular (e.g. PVS-14), and operating an IR laser at the same time. The OD 5 lens should filter out all IR radiation making the IR laser "dot" and "beam" completely "invisible" to your night vision. Pull the OD 5 lens away from the objective of your night vision device, operate the IR laser again, and you should see the IR laser dot and trace through your night vision device.

IR-V

 

[IR-V]

Re: Eye damage from reflection of 3B IR laser

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: icedragonmx</div><div class="ubbcode-body">Thank you very much IR-V! I will be doing some research on this before I start. I do appreciate you taking the time to give such a well informed response to my questions. Thanks! </div></div>

My pleasure to help with any info that will help keep your eyes safe, icedragonmx!

IR-V

 

[cj7hawk]

Re: Eye damage from reflection of 3B IR laser

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: McCourt Munitions LLC</div><div class="ubbcode-body">Using any kind of collective optics (rifle scope, binoculars, etc?) while lighting up targets? If so then you'll need to factor that in also.
</div></div>

Just to add to this briefly, since it didn't get addressed directly in the other posts; For a quick read that is worthwhile for anyone who is going to use lasers, read this.

http://www.operationalmedicine.org/TextbookFiles/batbooka.pdf

Section 6 - Laser Safety.

It also has a quick reference chart on the NOHD both with and without optics for most common military laser types.

Regards
David

 

[FCS]

Re: Eye damage from reflection of 3B IR laser

IR-V and CJ-7 have covered this in great detail. I don't know as that I can add all that much.

I will say that "eye-safe" military systems are a bit of a misnomer. I'm going off of memory but about 1350nm the light energy will be abosrbed by the aqueous vitreous (cornea), without proper eye protection your cornea can/will be burned. If burn is not sever, the cornea will recover. Higher powered system or lower power system with a longer exposure and it is very possible to blister the cornea.

I'll fully admit, most of the laser systems I worked on were class IV with power levels in the 10s of watts CW to mega watts peak power in modelocked, ultrafast pulsed systems. 3B laser system were the alignment/pointer beams for the larger systems I worked on. I'm probably a bit over the top the eye safety, have friends/coworkers with burns on their retina from one little screw up.

I apologize, just got a phone call and need to go. I'll try to get back to this a bit later.

 

[george etter]

Re: Eye damage from reflection of 3B IR laser

I have always believed forums can be be a source of both entertainment and very special hard to obtain knowledge . Thank you IR-V cj7 and McCourt for a very informative presentation .


Ernest Stuhlschuter