100-attosecond synchronization of two-color mode-locked lasers by use of optical phase locking

Abstract

Growing interest in ultrafast electronic processes in atoms, molecules, or condensed matters has driven shortening of the duration of ultrashort pulse lasers. Recent demonstration of attosecond pulse generation by high-order harmonics has opened a new frontier to so-called attosecond science [1],[2]. Fourier synthesis of optically phase-locked multicolor pulses [3]-[5] is also an attractive method of attosecond pulse generation because of its scalability of repetition rate or pulse energy. It would be possible to synthesize arbitrary electric-field waveform including attosecond pulse shape by superimposing several phase-locked ultrashort pulses with separate spectral components which range far beyond an octave. In recent years, the optical phase locking among multicolor pulses has been realized by a femtosecond optical parametric oscillator [6],[7] and two-color synchronized mode-locked lasers [8]-[10]. Obviously, stable phase locking and reproducible waveform synthesis require tight synchronization of pulses with a very low timing jitter. Until now, several groups have reported synchronization of two mode-locked lasers by active [11]-[14] and passive [15]-[18] schemes. In active scheme, the laser cavity is actively controlled with the electronic feedback circuits to minimize the relative timing jitter. Schibli et al. demonstrated active synchronization of Ti:sapphire and Cr:forsterite mode-locked lasers with a timing jitter as low as 300 as [14]. © 2007 Springer-Verlag New York.