# Inside a laser apparatus, the stimulation and relaxation of electrons in atoms causes many photons with the same what to be continuously emitted?

Jun 6, 2017

Wavelength.

We find that this is a word bank problem...

Of course, if we were to guess at it, we might have said wavelength or frequency, since we are talking about light here, but the question in the link gives wavelength as one of the words.

This is the case because energy levels are quantized (fixed at energies corresponding to integers), so if you have relaxation of electrons from their so-called virtual states, we expect to see light of the same wavelength many times, whether they are:

• the same wavelength $A$ each time,
• the same wavelength $B$ each time,
• $\vdots \text{ "" "" "" "" "" "" "vdots" "" } \vdots$
• the same wavelength $Z$ each time.

corresponding to each difference in energy going from each energy level to the ground state, $\Delta {E}_{A \to \text{grd}}$, $\Delta {E}_{B \to \text{grd}}$$, . . . \Delta {E}_{Z \to \text{grd}}$.

This is demonstrated by, well, firing the laser and seeing that it has a very focused beam, generally of a single color, i.e. wavelength. The best lasers fire light of a single color.

For example, here's a green laser, $\text{532 nm}$ light:

The reason why it's green is because few photons of different wavelengths are emitted in comparison to the green photons, and thus the light distribution is dominated by photons of green wavelengths.

You even see this in laser pointers. Here's a red one, around $\text{600 nm}$ light: