During the first part of the project, we developed a single-frequency (SF) tunable MOPA laser at 910m-940nm, with more than 2 W output power based on a non-polarization maintaining Nd-doped fibre. We studied the relative intensity noise (RIN) of the laser, and we compared with a numerical model previously used and validated in Ytterbium doped fibre MOPA lasers. The scalability of the system was limited by the presence of power instabilities. We tested different configurations, with 1 and 2 stages in order to reduce this effect. Also, fibres with different concentration of dopant were tested.
In the next phase of the project, a new developed PM version of the Nd fibre was used for upgrading the system. However, the instabilities effect observed in the non PM fibre was increased. After different tests we conclude that the problem could came from the fibre properties, in terms of Nd concentration and polarization dependence gain. As contingence plan, different approaches were exploded such as the use of taper amplifiers or even the opening of a new collaboration with the Lawrence Livermore National Laboratory, in order to use an experimental micro-structured Nd doped fibre. A laser version was developed with this last fibre in order to continue in parallel with the second harmonic generation. We reached more than 400 mW of blue radiation at 461 nm. In the last period of the project, the LMA developed from Ixblue was delivered. However just preliminary tests were carried out for lack of time, but showing promising results.
The knowledge and skills synergies generated along this project, contributed to the development of SF MOPA fibre lasers based on others rare earths doped fibres. In this regard, a 25 Watts single-frequency MOPA fibre laser emitting at 1120 nm was developed by heating up to 75ºC the Yb-doped fibre, in order to reduce the ASE at 1060 nm. Also, a 50 Watts low-noise SF laser operating at 1013 nm was developed. This system was designed to remove wavelengths between 1020-1060 nm by using an in-fibre filter. Also, a 1Watt all-fibered laser source at 852nm for focused ion beam (FIB) experiment based on cold Cesium atoms was developed. The system is based on the sum-frequency generation of 1540 and 1908 nm lasers. These lasers are based on doped fibre MOPA technology, with Erbium in the case of 1540nm and Thulium for the 1908nm one.
A collaboration with the Public University of Navarra (UPNA) and Instituto de Óptica group from the Consejo Superior de Investigaciones Científicas (CSIC), mainly focused on the study of relative intensity noise in random distributed fibre lasers (RDFL). This collaboration showed interesting and promising results which can contribute to the understanding of RIN behaviour in this kind of lasers. In this research line, we also developed the first random fibre laser at 532 nm with an output power up to 1.5W. The system combines a random fibre laser at 1064 nm based on Yb-gain as seed, an Yb-doped fibre MOPA for boosting the signal and a period poled lithium niobate (PPLN) crystal for the second harmonic generation. A first elegant prototype has been developed for testing in high resolution microscopy (work in progress).
Along the full project we generated 5 publications in international high-impact journals such as Optics Express, Optics Letters and Laser Physics Letters (open access version available for all of them), has been published. Currently, two papers are in generation progress to be submitted to high-impact journals. Also the work has been disseminated by participating in the most important conferences in lasers.
