Once one of them spontaneously emits a photon, it'll stimulate some of the others to do so, and you get a nice cascade of illumination.

讓它們激發而足夠產生光。當其中一個原子自發地放產生一個光子,它會刺激其他原子一起產生,然後你就會得到一層好的光

But instead of letting all the light escape, it's more powerful to trap it between two mirrors and let it to bounce back and forth through the atoms.

但是比讓所有的光逸散有用的是,用兩面鏡子把光子困住

All that passing light will stimulate them to emit even more light, and as long as you keep on re-exciting the atoms, they're happy to go on emitting light forever.

且讓它在原子裡來回彈跳。所有通過原子的光會刺激它們產生更多的光,而且只要你持續刺激原子,它們會持續發光直到永遠。

But why do the atoms emit light just because another photon passes by?

但是為什麼原子放出光僅僅只因為有光子通過? 這其實相當

It's actually pretty simple.

Imagine flipping two coins: they can either be in the same state,or in different states., but photons aren't like coins - no matter how hard you try, you can't tell one apart from another.

想像一下擲兩個硬幣:它們可以在同一面(同一狀態), 或是不同面(不同狀態)。但是光子不像硬幣,不論你怎麼試,你都不能分辨這兩個光子。

So in a "photon-flipping" experiment, that means there's only one way for them to be in different states but two ways for them to be in the same state.

所以"擲光子"的實驗代表只有一種情況讓它們處於

So they're more likely to be in the same state, and in general, this implies that photons always want to be like other photons - to have the same phase, polarization, and go in the same direction.

不同的狀態;兩種情況在同一狀態。所以光子比較有可能處於同一狀態之下,一般來說,這表示光子總是希望成為其他的光子 來擁有相同的相位,極化方向,以及相同的行進方向。

And what's more amazing is that if a solitary photon passes by an excited atom that could emit another photon, there's a good chance it will emit one because the two photons want be together - even before the second one exists.

更驚人的是,如果一個單獨的光子穿過一個可能會產生光子的激發態原子,這樣很有可能會使它真的產生光子,因為光子傾向於在一起,即使第二個光子還沒存在。

So once you have all these friendly photons bouncing around between the mirrors, you can just open up a little hole at the end and let out a blinding stream of coherent light - a laser beam.

所以只要你有這些在鏡子之間彈跳的光子,最後你就可以只開一個小洞,一束同調光就會出來:雷射光

To see lasers in action, check out this sweet episode of "Smarter Every Day" showing a laser you can stick your hand inside!

要實際看雷射光的話,看看"Smarter Every Day"的其中一集,

They also have a bunch of other cool science videos.

你可以把手固定在雷射裡面!這個節目還有很多其他很酷的科學影片。