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Old 08-04-2007, 12:15 AM #1
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Default physics experiment

hey guys ive just conducted a physics experiment dealing with converting laser energy back into electrical energy. ive only just done the testing but i can tell you its not very efficient but it does produce some results. We used two lasers, a green and my homemade dvd burner red firing across my house onto a solar panel. it will be some weeks but ill post my experimental write up here with all details and pics and such. tho i will note now that the red laser was more efficient than the green, i suppose this will all come back to the wavelength and the photoelectric effect after all .


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Old 08-04-2007, 01:00 AM #2
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Default Re: physics experiment

well the red is a direct diode, where the green is going from a diode to a crystal, to another crystal and then through a filter, so you loose at least 60% ( and more likely 80%+ ) of the energy just converting the light from one wavelength to another.

Most green 5mw pointers use a 250-300mw pump. the reds are 5mw right from the diode, no waste at all. they are incredibly efficient.
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Old 08-04-2007, 01:39 AM #3
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Default Re: physics experiment

sorry i probably did not give a good description, both lasers were 50mw lab lasers so there was near 50 mw hitting the panel of both colors .. also white light has a higher red component than green so i assume a solar panel is made of a material that is more efficient for red wavelengths than the green and thus a red wavelength will cause a larger current/voltage to flow.... im not sure i suppose ill have to investigate.... it might be that the red wavelength is less affected by airborne particles or something.... any help on the physics of a solar panel would be AWESOME
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Old 08-04-2007, 02:05 AM #4
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Default Re: physics experiment

Why does "white" light have a higher red component ?? "White" light from most flourscent tubes has a strong green spike -- That's why old film pictures looked sorta green. Light from the sun carries a lot of red and IR -- maybe that's what you are summing up.

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Old 08-04-2007, 02:10 AM #5
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Default Re: physics experiment

thanks mike yes i did mean light from the sun . also i have found that typical silicon solar panels are far more sensitive to the red and infra red (would it be better to call those the red spectra? or am i just getting to fancy )
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Old 08-04-2007, 02:45 AM #6
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Default Re: physics experiment

Well you cleared that up !! The silicon cell is sensitive beyond visible range. So the red and near IR is its peak. That's why my Sper Scientific power meter has peak sensitivity at 900 nM and drops to about 66% at 532 nM. You need to get the specs on your sensor.
Also, a sharp point on the sensor may not hit a "sweet spot" so covering a larger part of the sensor with a more diffuse beam may help. Reflection from the surface may also limit efficiency - Look for a reflected spot and measure lost power.

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Old 08-04-2007, 03:08 AM #7
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Default Re: physics experiment

my panels are old but i should be able to get some fairly in depth specs i hope... also in the experiment i used a small beam (5mm) and a beam that covered all the material on the solar panel (took ages to aim and focus right) for both red and green.... the wider beam was way less efficient, i assume it looses a great deal of energy due to the greater number of particles it would encounter in the larger volume of air that the wider beam would have traveled through (looong sentence there lol) also glad u mentioned the "sweet spot" for a focused beam, i tested on several different areas on the solar panel and found that it was the same as long as it hit in the center of one of the panels (solar panel had 6 individual panels on it). as for reflections, the surface of the panel i used has an anti reflective coating on it which almost totally avoided this problem and i found that the reflected amount of energy was very small and even when directed back with tinfoil it didn't seem to make a difference on the multimeter.
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Old 08-08-2007, 01:24 AM #8
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Default Re: physics experiment

I'm just saying that even with lab lasers, the power going in on one side is never going to come out the other, not even the aperture.

the energy to create 50mw of green via dpss is much higher than a direct injected red. also just the air and humidity can seriously affect the results. try using a plexiglass tube filled with nitrogen or argon, or some other inert gas.

you might also try comparing a light bulb either cfl or incandescent with a reflector setup and figure that in as well.

silicon isn't a good way to measure lasers, it's good for a cheap rough estimate but you really need a calorimeter. that way it absorbs almost everything and gives very accurate results not matter what is hitting it.
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Old 08-08-2007, 06:11 AM #9
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Default Re: physics experiment

the lasers were outputting almost exactly 50mw its not the input that was being measured. lol if i had all this fancy equipment it would almost remove the need for my experiment, as im looking at factors that are effecting the ability to transmit the energy and convert it and not trying to optimize this procedure. as this unit in physics addresses complex reasoning it means that i have to attempt to explain unknowns using physics theory so if i optimized this experiment while being a good way to try to invent something it probably would not show the analysis skills that the teachers expect. just looking at humidity i mean if i removed it from the procedure (firing through an inert or evacuated enclosure) then i would not be able to address how this effects the results. I could do one through an ideal space like an inert gas but i don't have the access to materials that i would need.

though looking at this it can be a very fine line between physicist and inventor however i believe a physicist finds out the "why" and the factors that effect it and the inventor tries to maximize results using the theory's to create a product.

If i had the materials and the time i would probably fire many many wavelengths through varying conditions onto many different surfaces and Analise the practical vs ideal. however as i don't have either time or the materials, i have aimed for more specific conditions and aiming to Analise these and theorize about the conditions and their effects.

I do like the idea about the alternate (would the opposite of mono chromic be polychromic?) light sources however as I'm going on a ski trip next week i do not have the time to widen my results any further.

ps please excuse the horrific grammar im not much of an English student .
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Old 08-08-2007, 07:13 AM #10
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Default Re: physics experiment

Sorry to say it, but this experiment seems to be fundamentally flawed to me. First off, if you haven't measured both lasers and determined they both put out a constant, unchanging output of 50mW independent of time, the whole thing is invalid from the start.

Also, I disagree with the conclusion that the diverging beam is more susceptible to losses in air. In either case, those losses should be nearly negligible. However, unless the glass on the solar panel is coated to be nearly 0% reflective at both wavelengths, the increased angle may be increasing the quantity of light reflected.

And of course, as was said above, those numbers are specific to that one type of material only. A different material may find much higher efficiency at 532nm than red.

Those criticisms said, I guess its still an interesting thing to be testing. It would be interesting to see what the effects on output are as you begin to oversaturate the cell (IE focus the beam and move the panel closer and closer to the focus.
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Old 08-08-2007, 08:23 AM #11
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Default Re: physics experiment

:P i suppose reading my posts the experiment does seem flawed however i just haven't bothered to do full procedure on what i have been doing. the lasers were measured by a laser power meter that i was able to borrow from my teachers old uni and were very consistent , also as for the lens system to diverge/focus the beam both focused and unfocused were fired through it (naturally) and i did brief checks to look at the efficiency of the lenses and the losses were very marginal and relitivly (i really cant spell) equal for both parts of this experiment. i am aware however that these are FAR from ideal circumstances, however for a school project, it seems a perfect experiment is not the way to go sadly. mainly because they seem to value overcoming errors in an experimental write up more than removing them from the experiment. also this is meant to be a small scale practical investigation where im analyzing efficiencies of easily obtainable items and merely have to comment on more advanced issues and how they would effect the experiment.

though you raise a good point with the losses in air.... well u raised many good points, but more worrying with the losses in air point.....though outside of school when i can get into the uni my experiment should be allot more valid scientifically though admittedly less valuable in a school project sense.

gee im really bad at conveying things in writing.... lol i read my posts and half the time i think ....what.....
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Old 08-10-2007, 03:32 AM #12
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Default Re: physics experiment

Quote:
Originally Posted by Thories
:P i suppose reading my posts the experiment does seem flawed however i just haven't bothered to do full procedure on what i have been doing. the lasers were measured by a laser power meter that i was able to borrow from my teachers old uni and were very consistent , also as for the lens system to diverge/focus the beam both focused and unfocused were fired through it (naturally) and i did brief checks to look at the efficiency of the lenses and the losses were very marginal and relitivly (i really cant spell) equal for both parts of this experiment. i am aware however that these are FAR from ideal circumstances, however for a school project, it seems a perfect experiment is not the way to go sadly. mainly because they seem to value overcoming errors in an experimental write up more than removing them from the experiment. also this is meant to be a small scale practical investigation where im analyzing efficiencies of easily obtainable items and merely have to comment on more advanced issues and how they would effect the experiment.

though you raise a good point with the losses in air.... well u raised many good points, but more worrying with the losses in air point.....though outside of school when i can get into the uni my experiment should be allot more valid scientifically though admittedly less valuable in a school project sense.

gee im really bad at conveying things in writing.... lol i read my posts and half the time i think ....what.....
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lol sorry im drunk, but i read every word of this and still dont know which one did better!!!! the red or green?

P.S. I did however understand the way the test was performed, equal lasers and all that.
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Old 08-10-2007, 05:58 AM #13
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Default Re: physics experiment

lol frosty, seems like ya having fun ay? the red was better in this experiment mainly because the solar cell was more sensitive to the red-infra red frequencies. sooooo ahhhh... keep on ninja-ising it up dude.
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