MAP PHYSICS LAB · LASERS · MAP 19

From one photon to a laser beam

Can you turn a quiet active medium into a working laser? Adjust the pump and mirrors, watch the light build, then investigate what makes it possible.

Can you make it lase?

Increase the pumping and find a mirror setting that produces a sustained output beam. Keep it running for three seconds.

Start with the pump. Watch the excited atoms build up.

One atomic event

Photon energy hν = E₂ − E₁.

Photon balance

Absorption

Energy levels on the left; a schematic photon interaction on the right. On small screens the views stack.

Pump and mirrors

Relative pump setting, not watts.

0%: fully reflecting. 100%: feedback removed.

Teal atoms are excited; grey atoms are in the ground state. Try changing one control at a time.

Your laser cavity

1 · Pumping2 · Inversion3 · Laser output
Metastable stateGround stateLaser light
Explore the physics

Compare populations, inspect the output graph, or load an example.

Estimated pump threshold

Gain must overcome the cavity losses. Presets use 20% mirror transmission.

Population inversionCompare the metastable and ground-state populations.
Metastable population
Ground population
Relative output

PREDICT → TEST → EXPLAIN · 1 / 3

Choose a prediction, then test it in the cavity.

Try this:

Show explanation

Teaching model: ideal discrete atomic transitions and a simplified three-level laser with rapid relaxation from the pump level to a metastable level. The upper pump level has negligible stored population in the rate model. The laser transition returns to the ground state; other laser designs use different level schemes. Equal statistical weights and absorption/emission coupling are assumed. Time, rates and output are rescaled model units. Dots and wave packets are illustrative, not literal particle counts or measured field patterns. A small spontaneous-emission term seeds cavity light. The plotted output can include weak spontaneous light below threshold. The model does not resolve cavity modes, phase noise or beam divergence. Laser components and level schemes.