Date: Tue, 10 Aug 2010 11:17:44

Author: Adam Beehler

Subject: Re: IR Leak from Green Laser Pointers

Post:

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Brian,

Interesting! I just tried all of that out as the last thing I did
yesterday before I went home. I had just searched the web for the
upcoming Perseid meteor show August 12-13 and ran across the same
article you linked:
http://tinyurl.com/2fl6wr3
My results are that, yes, my cameras, including my cellphone, see near
IR (like from remote controls). (This is a great fast way to check the
batteries in a remote control, even though I already bought one of those
little cards that you can aim the remote at to see flashes of light.)
However, my two green laser pointers reveal no IR in their diffraction
patterns. The lasers are from two different companies and extremely
different powers. Of course, I did not expect to see any IR either.
One laser is <5mW and the high powered one does indeed have an IR filter
(I already learned that). I was kind of hoping that I would see some
IR just so I could see the experiment work, but I guess it is good that
I did not. I do intend to use this simple little experiment to test
others green lasers.

Adam Beehler



Cudnik,Brian wrote:
>
> I was catching up with my e-mails this morning and found the following
> with the links below. I immediately tried the exercise described in
> one of the articles (but using a 600 lines / mm transmission grating
> in a darkened room, shining the laser thru the grating and onto the
> wall, the setup described used a CCD) with my own green laser pointer
> and cellphone (a Sanyo Katana eclipse flip-phone) camera, but no IR
> spots showed up in the diffraction pattern. Please read on for more
> information ...Brian Cudnik
>
> Some green laser pointers may be leaking IR light that we can't see
> but can still do retinal damage. Laser pointers are not to play with
> in general but here is a new twist on the dangers of laser pointers
> and a cool way to detect IR light on the cheap.
>
> I learned from one of the scientists at the Lunar & Planetary
> Institute this summer about the sensitivity of CCD arrays to infrared
> light. I was there with some other astronomy teachers. The CCD setups
> of most cameras have a wider spectral range than that our eyes. This
> means that things like web cams and phone cameras already pick up some
> IR light. In fact expensive cameras often have IR filters to block out
> the invisible frequencies.
>
> This was something I didn't know and an experiment with my DirecTV
> remote and my iPhone 3GS showed how easy it can be to see IR light
> sources that are otherwise invisible to me.
>
> Well the Sky & Telescope observing blog has a post about how our
> favorite green laser pointers can actually emit retina-threatening
> levels of IR light. When I did a simple test with a my 2 green laser
> pointers I could indeed see the green light but there was also a lot
> of IR light which shows up as a purplish-blue hued light. These were
> not cheap laser pointers. One is from the guys at Land Sea and Sky and
> one is from a science teacher catalog. Not the sort of places I expect
> shoddy merchandise. The NIST article mentioned in the post says
> quality laser pointers should have the IR leak. Mine didn't seem as
> profound as the images in the post but there was some IR according the
> iPhone.
>
> What this means is you can get an eyeful of dangerous IR light that
> you can't detect visually. There would be no instinctive reaction like
> blinking or shielding your eyes like would happen with visible laser
> light. There are a lot of factors that can bounce IR light in an
> unpredictable way. The article mentioned energy-efficient windows as a
> bad place to shine your IR-leaking light since they can reflect back
> IR very well but really just about anything can send light every which
> way. I am going to be even more careful at star parties than before.
>
> I have some ideas on how to use this concept in astronomy class and to
> talk about laser-pointer safety. The article also has a cool DIY
> diffraction setup that uses a CD. The diffraction fringes do indeed
> show up with this setup. Give it a try.
>
> Check out the S&T post.
> http://www.skyandtelescope.com/community/skyblog/observingblog/99956999.html
>
> Check out my images of the DirecTV remote from my iPhone 3GS.
> http://www.jimmynewland.com/2010/07/13/unknown-moon-day-1-you-can-see-ir-with-a-camera-phone/
>
> J Newland
>
>
>
>
>
> ------------------------------------------------------------------------
>
>
>


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Brian,

Interesting! I just tried all of that out as the last thing I did
yesterday before I went home. I had just searched the web for the
upcoming Perseid meteor show August 12-13 and ran across the same
article you linked:
http://tinyurl.com/2fl6wr3
My results are that, yes, my cameras, including my cellphone, see near
IR (like from remote controls). (This is a great fast way to check the
batteries in a remote control, even though I already bought one of
those little cards that you can aim the remote at to see flashes of
light.) However, my two green laser pointers reveal no IR in their
diffraction patterns. The lasers are from two different companies and
extremely different powers. Of course, I did not expect to see any IR
either. One laser is <5mW and the high powered one does indeed have
an IR filter (I already learned that). I was kind of hoping that I
would see some IR just so I could see the experiment work, but I guess
it is good that I did not. I do intend to use this simple little
experiment to test others green lasers.

Adam Beehler



Cudnik,Brian wrote:













I was
catching up with my e-mails this
morning and found the following with the links below. I immediately
tried the
exercise described in one of the articles (but using a 600 lines / mm
transmission grating in a darkened room, shining the laser thru the
grating and
onto the wall, the setup described used a CCD) with my own green laser
pointer
and cellphone (a Sanyo Katana eclipse flip-phone) camera, but no IR
spots
showed up in the diffraction pattern. Please read on for more
information …Brian
Cudnik
Some green laser
pointers may be leaking IR light
that we can't see
but can still do retinal damage. Laser pointers are not to play with
in general but here is a new twist on the dangers of laser pointers
and a cool way to detect IR light on the cheap.

I learned from one of the scientists at the Lunar & Planetary
Institute this summer about the sensitivity of CCD arrays to infrared
light. I was there with some other astronomy teachers. The CCD setups
of most cameras have a wider spectral range than that our eyes. This
means that things like web cams
and phone cameras already pick up
some
IR light. In fact expensive cameras often have IR filters to block out
the invisible frequencies.

This was something I didn't know and an experiment with my DirecTV
remote and my iPhone
3GS
showed how easy it can be to see IR light
sources that are otherwise invisible to me.

Well the Sky &
Telescope
observing blog has a post about how our
favorite green laser pointers can actually emit retina-threatening
levels of IR light. When I did a simple test with a my 2 green laser
pointers I could indeed see
the green
light but there was also a lot
of IR light which shows up as a purplish-blue hued light. These were
not cheap
laser pointers. One is from the guys
at Land Sea and Sky and
one is from a science teacher catalog. Not the sort of places I expect
shoddy merchandise. The NIST article mentioned in the post says
quality laser
pointers
should have the IR leak. Mine didn't seem as
profound as the images in the post but there was some IR according the
iPhone.

What this means is you can get an eyeful of dangerous IR light that
you can't detect visually. There would be no instinctive reaction like
blinking or shielding your eyes like would happen with visible laser
light. There are a lot of factors that can bounce IR light in an
unpredictable way. The article mentioned energy-efficient windows as a
bad place to shine your IR-leaking light since they can reflect back
IR very well but really just about anything can send light every which
way. I am going to be even more careful at star parties than before.

I have some ideas on how to use this concept in astronomy class and to
talk about laser-pointer safety. The article also has a cool DIY
diffraction setup that uses a CD. The diffraction fringes do indeed
show up with this setup. Give it a try.

Check out the S&T post.
http://www.skyandtelescope.com/community/skyblog/observingblog/99956999.html

Check out my images of the DirecTV remote from my iPhone 3GS.
http://www.jimmynewland.com/2010/07/13/unknown-moon-day-1-you-can-see-ir-with-a-camera-phone/

J Newland

















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