We all know that many lasers with special wavelengths are pumped out, so do you know how it works? Let's take a look at it together.

Pump laser is not a specific type of laser, but an excitation mode. The so-called "pumping" is actually to provide energy to "working substances" (such as solid crystals, optical fibers, semiconductor materials, etc.), so that the electrons in it "jump" from low energy level to high energy level. When these electrons accumulate to a certain amount and then fall together to release energy, stimulated radiation, that is, laser, can be generated.

Where does the pump light source come from?

Now the mainstream laser diode pumping (LD pumping), especially in solid-state and fiber lasers.

Because LD pump has high energy utilization rate, small volume, long life and is easier to control. For example, Nd:YAG laser usually uses 808nm laser diode as pump light source.

After the pump light shines on the working medium, the electrons inside the medium absorb photon energy and transition from the ground state to the excited state. This process is called stimulated absorption.

However, not all electrons can absorb suitable photons, and the pump wavelength must be matched with the absorption peak of the medium. For example, Nd:YAG crystal has the strongest absorption at 808nm, which is why LD pump uses 808nm.

When the electrons accumulate to the high energy level, some of them will naturally fall back to the low energy level to emit light (this is called spontaneous emission), but the key of the laser is to make these electrons "stimulated" by external photons and fall down at the same time to form stimulated radiation, and the photons released at this time have the same direction, phase and frequency, which makes it a laser.

What role does the resonant cavity play in it?

If light wants to become laser, it must be reflected and amplified back and forth in the resonant cavity.

Two mirrors will be plated on both ends of the working medium: one is highly reflective and the other is semi-transparent.

Light travels back and forth in it, and every time it passes, it will make the stimulated emission stronger, and finally it will be output from the semi-transparent surface.

It's like shouting in an echo room, and the sound is constantly reflected and amplified, and finally a "light beam" with direction and energy is formed.

The above is the working principle of pump laser. If you still don't understand, please feel free to contact us.