Compact femtosecond Cr:YAG laser

Research project P 14704 Compact femtosecond Cr:YAG laser Irina T. SOROKINA 09.10.2000 This project is aimed at extending the highly successful ultrashort pulse laser technology based on mirror- dispersion -controlled (MDC) Ti:Sapphire, Cr:LiSAF and Cr:LiSGaF oscillators into 1.5 m region. This challenging task is to be accomplished by combining the accumulated substantial knowledge of novel laser materials, diode-pumping, and mode-locking techniques, based on the implementation of dispersive dielectric mirrors and novel saturable-absorber material systems using semiconductor-doped-silica films. The research will be focused on development and investigation of compact femtosecond MDC Ci4+:YAG laser at 1.5 microns. In particular, it is intended to realize a directly diode-pumped Cr4+:YAG laser, delivering more than 300 mW in cw- and about 100 mW in modelocked regimes. By optimization of the mirror dispersion and using the newly developed mirrors with exceptionally low losses, shortening of the pulse-duration down to 20 fs is envisaged. A high-power Yb-fiber laser pumped version of the Cr:YAG ferntosecond oscillator should deliver 0.5- 1 W of output power. In close relation with the work on ferntosecond oscillator an extensive spectroscopical investigation of Cr 4+: YAG and related Cr4+-doped materials will beperformed in close collaboration with crystal growth laboratories, aimed at solving the problem of "slow bleaching" and increasing the working Cr4` concentration. In the framework of this project it is planned to prepare two PhD dissertations in laser engineering and spectroscopy.

In frames of the project the first directly diode-pumped mirror-dispersion-controlled (MDC) femtosecond laser has been developed that operates around the 1.5 m wavelength. The laser is based on the Cr4+:YAG crystal. Besides the laser technology, working on the project also bolstered advances in fundamental research areas like material science and physics of ultrashort optical pulses. For the first time a compact source of extremely short infrared light pulses consisting of only few optical cycles in the very interesting for many applications wavelength region could be demonstrated. The shortest pulses are only 25 femtoseconds (2510 -15 s) long, corresponding to just 5 optical cycles. As a directly diode pumped source of few-cycle pulses, this laser is the second device of this kind ever realized, and the first one in the eye-safe wavelength region. As a demonstration of the new possibilities, opening with the invention of such source, optical continuum generation has been performed using a short piece of optical fiber. The optical continuum, generated this way can be used for optical coherence tomography in medicine and for ultra precise frequency measurements. The Cr4+:YAG laser is one of the few coherent sources that are broadly tunable around 1.5 m and is therefore attractive for a number of applications in telecommunications (e.g. for pumping Raman amplifiers, or as a tester for fibers, and in WDM applications) as well as for remote sensing and trace gas monitoring. Moreover, the spectrally broadened pulses from these lasers can be readily applied to high resolution optical coherence tomography as well as state-of-the-art metrology.