[Cyborg] 200 laser diodes

Eric Boyd mrericboyd at yahoo.com
Sun Jun 6 21:45:31 UTC 2010

Yeah, that's a great idea.  If we monitor both electrical and optical power we can determine if the efficiency is always the same, which would then mean that electrical power translates directly to optical power.   It's also possible that we will discover that they don't vary much.


--- On Sun, 6/6/10, Christie Dudley <longobord at gmail.com> wrote:

From: Christie Dudley <longobord at gmail.com>
Subject: Re: [Cyborg] 200 laser diodes
To: "Mitch Altman" <maltman23 at hotmail.com>
Cc: "Eric Boyd" <mrericboyd at yahoo.com>, "Noisebridge-Cyborg" <cyborg at lists.noisebridge.net>, "Andy Isaacson" <adi at hexapodia.org>
Date: Sunday, June 6, 2010, 2:37 PM

I was curious... with the anticipated variation in strength... would you be able to estimate the power of the laser by the current it consumed?  I realize power in is not exactly equal to power out, but you'd have a pretty good gauge once you had a good benchmark, wouldn't you?  If that worked, it could be a fast, easy and consistent test of all those lasers you picked up.

"Great spirits have always found violent opposition from mediocrities. The latter cannot understand it when a man does not thoughtlessly submit to hereditary prejudices but honestly and courageously uses his intelligence." -- Albert Einstein

On Sat, Jun 5, 2010 at 12:25 PM, Mitch Altman <maltman23 at hotmail.com> wrote:

> Date: Sat, 5 Jun 2010 11:21:51 -0700
> From: mrericboyd at yahoo.com
> To: maltman23 at hotmail.com

> CC: adi at hexapodia.org; cyborg at lists.noisebridge.net
> Subject: Re: [Cyborg] 200 laser diodes

> Mitch Altman wrote:
> > > I have an interesting safety question: do you think that PWM controlling
> > > the lasers would actually make them eye safe? For instance, let's say

> > > we discover that the true optical power of the lasers is something like
> > > 10mW. Would it actually make them any eye safer to PWM control a laser
> > > to 50% duty cycle? Theoretically that reduces the "power" to 5mW, but I

> > > expect that in practice it's the peak intensity on your fovea that
> > > causes the damage, and PWM will not reduce the peak intensity. Thoughts?
> >
> > PWM definitely can reduce the effective light output. But, will these

> > laser diodes pulse at a high enough frequency to allow for PWM? We'll
> > just have to try and see.
> Actually, it's precisely the fast response of the lasers that I am 
> worried about. PWM can definitely control the average 

> electrical/optical power, but my understanding it that is isn't 
> necessarily the average that is dangerous. If you had a 1W laser, but 
> PWMed it to 5mW (so 0.5% duty cycle), I still wouldn't want to shine 

> that in my eye, I think it would be hella dangerous, much more dangerous 
> than a constant-strength 5mW laser. It's the difference between a bed 
> of nails and a nice mattress. It gets more dangerous the slower the PWM 

> is, of course. So maybe the trick is that we need to PWM as fast as 
> possible? Arduino PWM is only like 500 Hz, which isn't very fast.

Yeah, exactly.  Look at the extremes.  If the PWM is at 0.5Hz, that certainly wouldn't be OK, since 1/2 second of laser light focused on your retina would make most people very unhappy.  But if the PWM were at 1MHz, then it would be fine, as no amount of laser light we'll be obtaining can cause any damage in 1usec.  Of course, our PWM will be somewhere within those extremes.  Conceivably, one could do the math to determine the minimum amount of time for PWM period for a given amount of laser light that is safe (i.e., the amount of time it takes for the given amount of laser light to heat up your eye too much, and the amount of time it takes for you eye to cool down enough once exposed to that amount of laser light).  If this were PWM for an IR diode rather than an eyeball, the math is pretty easy (I over-drive the "safe" limit for IR emitters in my TV-B-Gone and have never had an IR emitter fail me yet).  But I don't know how to do the math for
 safety for eyeballs.  And the consequences are a bit more upsetting with eyeballs than a $0.14 IR emitter.  Anyone know how to do the math for eyeballs?  Or, are there studies that show the safety limits for given amounts of laser intensity?





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