[Cyborg] 200 laser diodes

Christie Dudley longobord at gmail.com
Sun Jun 6 20:37:41 UTC 2010

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?
> Mitch.
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