Gigahertz repetition rate, sub-femtosecond timing jitter optical pulse train directly generated from a mode-locked Yb:KYW laser.

We show that a 1.13 GHz repetition rate optical pulse train with 0.70 fs high-frequency timing jitter (integration bandwidth of 17.5 kHz-10 MHz, where the measurement instrument-limited noise floor contributes 0.41 fs in 10 MHz bandwidth) can be directly generated from a free-running, single-mode diode-pumped Yb:KYW laser mode-locked by single-wall carbon nanotube-coated mirrors. To our knowledge, this is the lowest-timing-jitter optical pulse train with gigahertz repetition rate ever measured. If this pulse train is used for direct sampling of 565 MHz signals (Nyquist frequency of the pulse train), the jitter level demonstrated would correspond to the projected effective-number-of-bit of 17.8, which is much higher than the thermal noise limit of 50 Ω load resistance (~14 bits).