Y'all are a bunch of wankers!

Can solar cells make use of a photonic cascade?

Supposedly this how lazers get primed. I was wondering if it would be a way for solar sells to extract more energy from the spectrum.
Permalink son of parnas 
March 27th, 2007 12:27am
photonic cascade?

LASER is an acronym, Light Amplification by Stimulated Emission of Radiation (not stricly accurate, a laser isn't really an amplifier, but the acronym was made to be parallel to MASER).

The Stimulated Emission part is that once one electron drops down in energy and gives off a photon, that stimulates another one, and so on and so on.  And the electrons are in a high-energy state because they've been pumped up there.

So yeah, there's a cascade, but first you put a bunch of energy in so that there's something to cascade.

In a solar cell, you don't have the same energy conditions, you're just sticking some Si out there, waiting for photons to hit it and bump some electrons up to higher energy levels, where they can be collected and then used.
Permalink Send private email Ward 
March 27th, 2007 1:15am
Lasers are so Bohring.
Permalink Send private email strawberry snowflake 
March 27th, 2007 1:43am
The early lasers worked with a flash tube in order to overload the atoms in a rod of synthetic ruby.  Solar cells don't have that burst of energy -- it's more constant.  So I'm not sure it could work.
Permalink Send private email xampl 
March 27th, 2007 6:38am
The description I read made it seem like a relatively small amount of energy in the right medium could cause the cascade. But I wasn't sure what small meant.
Permalink son of parnas 
March 27th, 2007 11:27am
Yes, a relatively small amount of energy in the "right medium" can cause a cascade.

And the "right medium" is a fog of Argon, or the right crystal, which has had the energy in its electrons already increased. 

In other words, energy has already been put INTO the medium, ready to be triggered by a relatively small amount of ADDITIONAL energy, to produce a Laser 'pulse'.

This scenario wouldn't really work for a solar cell, because I'm sure that original "energy pumping" entailed loss of efficiency.
Permalink SaveTheHubble 
March 27th, 2007 12:43pm
> because I'm sure that original "energy pumping"

The energy from the sun is there. Isn't that enough if collected over time?
Permalink son of parnas 
March 27th, 2007 1:50pm
What about "loss of efficiency" did you not get?

The point being, we want/need solar cells which are really efficient.  'wasting' some of that energy in order to reproduce a 'laser' 'photonic cascade' effect doesn't make sense.

Here's the December 2005 winner so far -- 40.7 percent.

http://www.energy.gov/news/4503.htm
Permalink SaveTheHubble 
March 27th, 2007 2:29pm
Also note that the 40.7% efficiency represents the conversion of light energy to electricity through the photoelectric effect. It neglects the energy inputs from the cooling system used in the demonstration that were needed to get that efficiency. So it's kind of like the state of fusion reactors nowadays - we can maintain a fusion reaction, but there is a cost to be had regarding the energy needed for the containment field.
Permalink Practical Economist 
March 27th, 2007 2:50pm
> What about "loss of efficiency" did you not get?

Charming.
Permalink son of parnas 
March 27th, 2007 3:03pm
Sorry about that, I get cranky in the afternoons.
Permalink SaveTheHubble 
March 27th, 2007 3:37pm
> wasting' some of that energy in order to reproduce a 'laser'

My understanding is most of the EM spectrum is wasted. Perhaps that energy can be used some other way.
Permalink son of parnas 
March 27th, 2007 3:42pm

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