Short-pulse tunable color-center lasers

Abstract

We review our recent results in the development of broadly tunable picosecond and femtosecond color center lasers operating in the near IR wavelength region. As active materials we use color centers with high optical gain in NaCl, KCl, and KBr hosts. All systems can be efficiently pumped with Nd:YAG laser lines. Using synchronous mode- locking, pulses with typically 5-10 picosecond duration and nanoJoule energy levels are obtained. The combined tuning range of these actively mode-locked lasers extends from approximately 1.4-2.4 micrometers without gap. In all cases the pulses are nearly bandwidth limited, with the notable exception of the NaCl laser. We show that coherent photon seeding can be used in this case to drastically improve the pulse quality by reducing high-frequency noise and spectral bandwidth. Pulses with femtosecond time duration, operating in the 1.5-1.6 micrometers range, are realized using passive mode- locking with semiconductor saturable absorbers. Using the absorbers in single- and coupled-cavity configurations, these lasers are particularly simple in that they require only a continuous-wave pump. Finally we demonstrate that the laser active color center systems can be used also as high- gain amplifiers. Employing a single two-pass amplification scheme, femtosecond pulses from a 1.5 micrometers oscillator are amplified to microJoule energy levels and used to generate femtosecond IR spectral continua.