Modes and Pulses

Standing waves and mode-locking

An interactive lesson with 6 steps, about 5 minutes: you predict, drag and solve, with instant feedback on every answer. It runs in your browser and needs JavaScript.

What you’ll learn

• Cavity modes are spaced by $c/2L$.
• Locking N modes in phase gives pulses about 1/N of the round-trip time long.
• Frequency combs turn mode-locked lasers into rulers for light.

Steps

1. Waves between mirrors
2. Mode spacing
3. Locking the modes
4. Light in a femtosecond
5. Shortest pulses
6. A ruler made of colours