Re: converting visible light to IR

"Bluespace Technologies" <bluespace@xxxxxxxxxx> writes:

"Sam Goldwasser" <sam@xxxxxxxxxxxxxxxxxx> wrote in message
news:6wk67jijdn.fsf@xxxxxxxxxxxxxxxxxxxxx
Phil Hobbs <pcdh@xxxxxxxxxxxxxxxxxxxxxxxxxxxx> writes:

Bluespace Technologies wrote:
"Sam Goldwasser" <sam@xxxxxxxxxxxxxxxxxx> wrote in message
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"Bluespace Technologies" <bluespace@xxxxxxxxxx> writes:


"Salmon Egg" <salmonegg@xxxxxxxxxxxxx> wrote in message
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On 6/12/06 9:01 PM, in article
sZSdnZoIx7NspRPZnZ2dnUVZ_tGdnZ2d@xxxxxxxxxxxx, "Bluespace
Technologies"
<bluespace@xxxxxxxxxx> wrote:


Ideally I would like to compress to a particular IR frequency like
950
nm,
or a single wavelength. Is that achievable using the Nd:YAG
crystals, or
otherwise?

Again, the grammatical construction of the question prevents it
from being
a
good question. My best guess of the questions meaning is that it is a
request convert broadband radiation into narrow band
radiation. If that is
the case, an optically pumped laser is called for. Broad band
light gets
converted into a much narrower band of lower frequency radiation. Who
knows
what is really being asked?

Bill
-- Ferme le Bush



Thanks for your responses, but unfortunately I'm not skilled
enough in the
area to pose the question as an optical scientist would.
I'm investigating an application that uses a device that collects
white
light from the surface of an LCD screen (typically a computer monitor,
or
other) and downconverts this light to something in the IR band to be
re-emitted. A narrow downconversion is preferred (ideally
somewhere between
850 to 1100nm) because that is the detectable range of the IR
photodiodes.
This downconverted signal is re-emitted to be detected by an array of
IR
photodiodes ultimately to calculate the position the white light
collector.
At this point I only care that white light can be converted to IR to
be
detected by the sensor array. Thanks for any help.

I may be misunderstanding what you are trying to do but would suggest
you search for "four quadrant position sensor" or something like that
to rule out that very simple solution to position sensing.

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We cannot find a PSD for the size required. Right now we use a
6-inch square screen with IR sensors on all edges. We can position a
knob device very linearly to 1mm accuracy using a battery powered IR
emitter tucked in the device. Even the knob's rotation can be
traced. The goal here is to get rid of the battery and use the LCD
screen as a light source to convert and emit IR. It may not work,
but if IR can be converted from LCD light and is bright enough, then
we likely don't need a battery.
-Andrew

What you need is a lens to image the screen down on your PSD. My
seaside holiday pictures use film frames that are considerably smaller
than the ocean!

I think he wants sense the position of his "knob device".

But then the lens has to be large enough to capture enough light to
generate
enough electricity to power the IR LED. There is no direct
optical-optical
process that will be efficient enough.

This sounds like you want to use a $1,000 solution to save on a $1
battery.
With auto-off, the batteries in wireless mice and such last a long time.

--- sam | Sci.Electronics.Repair FAQ: http://www.repairfaq.org/

Alright, optical-to-optical now we are talking about what i want to know.
Why is it not efficient? What degree or precent of efficiency will the light
convert? Any idea what crystal does this best?

The physics is against you. Materials absorb at very specific wavelengths
determined by their atomic structure and such. LCDs produces broadband
light. So, you lose a couple of orders of magnitude right there. You
absorb at a band 2 nm wide but your LCD produces light over 200 nm or more.

Second, you don't want to have a large absorbing surface or a large lens,
so the amount of light you can capture is extremely limited. The light
from the LCD goes out in all directions. What you can intercept with
a your device is a small fraction of the light produced.

Next, any photons that are absorbed and the reradiated at a longer wavelength
will be omnidirectional except under specific conditions that can't be met
here (phase matching in non-linear optics if you want to research it)
so you'd need some way of redirecting them to produce a beam you could use.

Any one of these things makes the thing impractical, if not impossible.
And there are other factors further reducing the efficiency.

Think of it this way: Try to run a solar calculator from the LCD light.
If it works at all, cover up all the solar cells by some fraction
representing how much area you can accept for your device. Report back. :)

--- sam | Sci.Electronics.Repair FAQ: http://www.repairfaq.org/
Repair | Main Table of Contents: http://www.repairfaq.org/REPAIR/
+Lasers | Sam's Laser FAQ: http://www.repairfaq.org/sam/lasersam.htm
| Mirror Sites: http://www.repairfaq.org/REPAIR/F_mirror.html

Important: Anything sent to the email address in the message header above is
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.

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