Attosecond timing jitter pulse trains from semiconductor saturable absorber mode-locked Cr:LiSAF lasers

Duo Li,James G. Fujimoto,Alphan Sennaroglu,Andrew Benedick,Franz X. Kärtner,Umit Demirbas

doi:10.1364/oe.20.023422

Abstract

The timing jitter of optical pulse trains from diode-pumped, semiconductor saturable absorber mode-locked femtosecond Cr:LiSAF lasers is characterized by a single-crystal balanced optical cross-correlator with an equivalent sensitivity in phase noise of -235 dBc/Hz. The RMS timing jitter is 30 attoseconds integrated from 10 kHz to 50 MHz, the Nyquist frequency of the 100 MHz repetition rate oscillator. The AM-to-PM conversion induced excess phase noise is calculated and compared with experiment. The self-steepening effect is proven to be the dominant AM-to-PM coupling mechanism, whereas the semiconductor saturable absorber operation does not adversely affect timing jitter. The results show that ultrafast Cr:LiSAF lasers are promising compact and efficient ultralow-jitter sources.

Highlights

Femtosecond mode-locked lasers have excellent noise properties
We report on timing jitter measurements of semiconductor saturable absorber mode-locked femtosecond Cr:LiSAF lasers and discuss the impact of relative intensity noise (RIN) and operating point of the saturable absorber on timing jitter
The rest of the dashed curve closely tracks the measured phase noise power spectral density (PSD). This suggests that the timing jitter of the Cr:LiSAF laser is currently affected by the intensity noise of the diode pump source, in that the pump RIN is transferred to that of the mode-locked laser, which is further converted into timing jitter

Summary

Introduction

Femtosecond mode-locked lasers have excellent noise properties. In particular, the extremely low timing jitter of optical pulse trains enables ultrafast lasers as ultralow jitter sources in numerous applications [1], including high precision synchronization of large-scale facilities [2], low phase noise microwave generation [3,4,5], high-speed, high-resolution optical sampling and analog-to-digital conversion [6]. Balanced optical cross-correlation (BOC) measurement techniques [10] provide a direct optical domain method to measure timing jitter with high sensitivity and sufficient temporal detection range This method has been utilized to completely characterize timing jitter up to the Nyquist frequency in passively mode-locked fiber lasers [11, 12] and solid-state lasers [13, 14]. It is important to investigate the AM-to-PM mechanisms and to understand the impact of the mode-locking regimes on noise properties of pulse trains from ultrafast solid-state lasers It is unclear whether temporal shifts of the pulses due to asymmetric pulse shaping by a slow saturable absorber significantly contribute to timing jitter.

Quantum-limited timing jitter of ultrafast Cr:LiSAF lasers

Characterization of timing jitter in the optical domain

Intensity noise and timing jitter

Findings

Conclusion