Optical and Quantum Electronics 28 (1996) 1773-1780 Bandwidth-limited time-synchronized frequency tunable double pulse generation in a branched picosecond Nd :glass laser O. STEINKELLNER, J. FURTHNER, A. PENZKOFER Naturwissenschaftliche Fakultdt II- Physik, Universitdt Regensburg, D-93040 Regensburg, Germany Received 29 April; revised and accepted 24 June 1996 Nearly bandwidth-limited, time-synchronized, frequency tunable picosecond pulses are generated in an active and passive mode-locked laser consisting of an Nd: silicate glass and an Nd : phosphate glass branch and a common antiresonant ring. An electro-optic Q-switch, an acousto-optic modulator and a saturable absorber in the antiresonant ring are responsible for mode locking and time synchronization. Three-plate birefringent filters in the gain branches are used for spectral narrowing (pulse duration broadening) and wavelength tuning. Pulses of 40 ps duration with a synchronization jitter of 10 ps are generated. A frequency tuning range from 0 to 350 cm -1 is achieved. 1. Introduction Time-synchronized frequency tunable powerful ultrashort laser pulses are needed for short- pulse non-linear optical frequency mixing (sum and difference frequency generation) [1-3] and coherent material excitation (coherent anti-Stokes Raman scattering [4, 5], coherent Stokes Raman amplification [6]). Picosecond and femtosecond parametric amplifier systems are widely used for the generation of powerful frequency tunable pulses that are time synchronized to the pump pulses [7-9]. Previously we reported on the generation of intense time-synchronized frequency tunable picosecond pulses in a mode-locked Nd: glass double laser system (pulse duration, 15 • 3 ps; synchronization jitter, cr t ~ 5ps; tuning region, 0-200cm-1; repetition rate, _<0.1Hz) [10]. A theoretical analysis of the laser system was given in [11]. The spectral width of the pulse trains was broadened (Ag E ~ 20cm -1) because of self-phase modulation [1] inside the laser. In this paper the Nd : glass double laser system is modified to generate intense nearly band- width-limited pulses of about 40 ps duration. The detrimental effect of self-phase modulation is reduced by elongation of the pulse duration and concomitant peak pulse intensity reduction. 2. Experimental procedure The experimental set-up of the laser oscillator is shown in Fig. 1. It consists of an Nd : silicate glass (Schott type LG680) gain branch, an Nd:phosphate glass (Schott type LG760) gain branch, and an antiresonant ring [12]. Two identical three-plate quartz crystal birefringent fil- ters are inserted in the gain branches. They are tilted towards the Brewster angle. The quartz- plate thicknesses are 1.25, 5 and 20mm. The optic axes are in the surfaces of the plates. 0306-8919 9 1996 Chapman & Hall 1773