# Saturated absorption: decrease size of material rather than intensity of light?

1. Feb 2, 2012

### franco1991

In saturated absorption, the decrease in absorption (and corresponding increase in wave transmission) is dependent on the intensity of the incoming wave. But why can't we decrease the size of saturable material, rather than the intensity of light?

According to my understanding, saturable absorption happens because there are more photons than atoms, thus the atoms cannot absorb all the impinging photons, and thus some photons will be transmitted. Is this the case? If it is, then couldn't we just decrease the size of material and thus decrease the number of atoms available to absorb the photons, rather than increasing the number of photons (by increasing the intensity of light)?

The only reason I could see this not working is if saturable absorption is some special phenomena, for example if at high energies the atoms are energized for longer than they normally are, and thus take longer to go back to ground state (which would mean that it does rely on actual intensity rather than the ratio of atoms to photons).

So, which one is it? Is it that the atoms take longer to get back to ground at high energies (in which case decreasing the # of atoms won;t do anything), or is it simply the ratio of atoms to photons, and there being more photons than atoms? (in which case, decreasing the number of atoms should have the same effect as increasing the intensity and thus number of photons in the impinging wave).