How Lasers Work Pt. 3

PART III: LASERS

See magic.

Now let's get back to business.

for the record

when we say lava, we mean the molten rock (like aa) and not such things as:
Laser Assisted Voice Adjustment (though this still falls in the category of lasers so I can see where the confusion comes from)
lamps (though the are sweet...so maybe they do count)
soap (Mike Huckabee supports it) or I guess soup (?) (I guess?)

Sorry to Interrupt

...but this helps show the importance of lasers:

http://overcompensating.com/posts/20041201.html

How Lasers Work Pt. 2

PART II: PHOSPHORESCENCE

We now move on to the slightly more interesting phosphorescence. In some cases, an intermediate energy state may be located between our two energy levels we've been discussing. So let's label our three states S0, S1, and S2 with energy gaps equal to E01, E02, and E12. Now if we use light of energy E02, we will excite ground state (S0) atoms to the second excited state (S2). These atoms may make a very fast transition to the first excited state (S1) without emitting a photon (a so-called radiationless transition, with the energy, E12, released in another form, perhaps heat). Now, if the transition from S1 to S0 is really unfavorable (a so called forbidden transition, usually implying a violation of spin conservation), then the relaxation from S1 to S0 will take a long time. Thus, we pump atoms up to a really excited state, they quickly come down to an intermediate state, and then slowly relax back down to the ground state, emitting light in the process - note: the energy of the light given off, E01, will not be the same as the energy we put in, E02, and in this way we can get cool colors of light from our atom. This describes phosphorescence: we shine light on our stuff, it starts giving off light of a different color, and even after we turn off our light, it continues giving off light for some time (because atoms are still in the intermediate excited state S1, and are taking a long time to come back down).

This is how some glow-in-the-dark materials work, namely those which have to be sitting in light for a while. The light 'charges' the material, getting atoms into excited (but forbidden) states, and then when you take the light away, all these atoms slowly relax back to the ground state, releasing light in the process. This process is especially useful for making really sweet stickers to put in your stickerbook.

How Lasers Work Pt. 1

This post begins what will probably be a three to four-part endeavor to explain the basics of how lasers work. Comments and questions welcome, I'll try to explain this all as simply I can. Additional details will be parenthesized and are only supplemental material not necessary for the understanding of each article, aka feel free to skip them.

PART I: FLUORESCENCE

To develop the background necessary for later parts, I will avoid lasers here and discuss the basics of energy levels and emission. Atoms and molecules have a discrete set of electronic energy levels (which may be obtained by the solution of Schrodinger's eigenvalue equation for the electronic degrees of freedom - if we do the same for the nuclear degrees of freedom we can obtain rovibrational energy levels, but from here on out, we'll ignore them). These energy levels can be ordered, with the lowest one being called the 'ground state.'

When left alone (i.e. thermal equilibrium), a majority of the particles will be in the ground state (with the ratio of particles in each state equal to the Boltzmann factor for the energy difference between the two states). If we add energy to the system, perhaps in the form of light, we can excite the ground state atoms into an 'excited state.' But the energy we add has to be exactly equal to the energy gap between the two states. Once our atom is in an excited state, it can very quickly relax back down to the ground state via the emission of a photon with an energy equal to the energy gap. In principle, this describes fluorescence: we shine light on something and it immediately starts giving off light. As soon as we turn off our light, fluorescence will stop because all of the excited state atoms will immediately return to the ground state.

This is basically how glowsticks work. Although rather than using light for the excitation, a chemical reaction occurs (when you snap the glow-stick, letting the chemicals mix) which releases energy, exciting a dye molecule. When the dye molecule relaxes back down to its ground state, it releases energy in the form of light. Once the glowstick runs out of chemicals, the reaction stops, and the glow-stick stops glowing. This is also when you cry and snap another glowstick to make yourself happy again.

Please ask questions, all 3 people who probably read this, and I'll do my best to answer them.

Next time - PART II: PHOSPHORESCENCE

The Master's Apprentice

As a student of science, I am, of course, very interested in lasers and lava. As such, I am quite fortunate to be attending New York University, home to one of the world's foremost experts in the field of lasers: Dr. Henry Brenner. He has revolutionized the field with in depth theoretical work and incredible applied usages. The military has sought him out on several occasions, and though he always serves his country when needed, he cannot be contained by their restrictions. His research will not be stifled. Through my classes with Dr. Brenner, I have learned that one must understand that lasers are not only the single greatest scientific achievement of man, but also the single most important art. There is a certain beauty and elegance that cannot be denied.
Dr. Brenner's laser research began at a young age and, in fact, he still has the first laser he designed while still in high school. A breakthrough in the field, I believe it is still more powerful than anything commercially or industrially available today.
Unfortunately, at this time Dr. Brenner is unavailable for interview. He is busy perfecting his latest endeavor and training for the next crisis.
Here are 5 interesting facts about lasers:
5. Lasers can be used to heat a Hot Pocket to incredible heats (sidenote: similar, in this regard, to lava; except lava adds much more flavor).
4. Because lasers can easily sever bone and destroy grey matter, they are excellent anti-zombie weapons, if properly used.
3. A MacGyver episode (season 5, episode 2) where he builds a makeshift laser is based on Dr. Henry Brenner's life.
2. The Vernier LabPro is compatible with several lasers and can easily complete even the most complex of experiments. Dr. Henry Brenner officially approves this device to initiate the beginner in the world of lasers.
1. Lasers make great stocking stuffers. Just keep the safety on.

Introduction (the Hypothesis)

Fact: all of science can be boiled down to one of two phenomena, lasers and lava. In addition to just being generally awesome, these two feats of physics comprise 98% of all useful science in effect today [citation needed]. This blog seeks to get the general public up to speed on modern laser- and lava-related science and technology. Expect explanations, applications, and more than anything, sweet pics courtesy of Google image. As a mere example of the ubiquity/badassness of lasers and lava, I include here, in this maiden-voyage post, the first hit from Google image for 'laser' and 'lava,' respectively. Enjoy.