Fig. 4: Self-starting high-harmonic emission. | Light: Science & Applications

Fig. 4: Self-starting high-harmonic emission.

From: Ultrafast response of harmonic modelocked THz lasers

Fig. 4: Self-starting high-harmonic emission.

a Free-running QCL spectrum showing several frequency bands separated by 100GHz corresponding to the 15th harmonic of the round-trip frequency. Each frequency band has a mode spacing corresponding to the second harmonic of the round-trip frequency. b Time-resolved electric field profiles with multiple pulses per round trip and an ‘over-modulation’ at half the round-trip time

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