Frequency stabilization and control of a mode-locked dye laser

Abstract

The mode comb of a synchronously pumped mode-locked dye laser is stabilized in frequency by locking one of its modes to a transmission maximum of a reference Fabry–Perot interferometer. The frequency error signal, obtained by a conventional modulation–demodulation technique, is fed back to permanently readjust the cavity length of the laser via an integrating servo amplifier and a piezo-positioned end mirror. Insertion of an appropriate loop filter prevents loop oscillations on the dominant mechanical resonance of the transducer–mirror combination. A special ramp automatic reset function is introduced to avoid saturation of the servo amplifier. To verify the improvement in laser stability the emission spectrum was scanned with a high-resolution optical spectrum analyzer. A laser linewidth of 3 MHz has been achieved. Extended linear sweeps of the stabilized mode comb for spectroscopic measurements were realized by simultaneously tuning the reference cavity and tilting the intracavity etalon.