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Report

Teaser, summary, work performed and final results

Periodic Reporting for period 1 - NeoLaS (Novel High-Power Single-Frequency Neodymium-Doped Fibre Lasers)

Teaser

Summary

Single-frequency lasers are crucial tools for a variety of applications such as atom cooling, metrology and sensing, among others. However, to date there are still uncovered wavelength domains due to technological challenges, especially in the 900-940 nm and 455-470 nm windows for applications demanding robust systems. This project mainly focuses on the investigation of novel high-power single-frequency lasers at these wavelengths. The outstanding features of fibre laser technology make it the best option to surpass the power limitations of other technologies. Before the beginning of this project, multi-Watt neodymium-doped fibre lasers were only demonstrated in a longitudinal multimode operation using resonant cavity configurations. The development of multi-Watt-level single-frequency lasers at 910-940 nm remains a challenge addressed in this project. NeoLaS has proposed a radical new approach which is based on novel exotic fibres doped with neodymium in a master-oscillator power amplifier configuration. Using this new approach, a single-frequency fibre laser tunable in the 915-937nm window and with more than 2 Watts output power has been demonstrated. Tests with especial large-mode area fibres for power scalability have been carried out achieving output power higher than 5W. Also, by second harmonic generation more than 400 mW of blue radiation was achieved. This project has pave the way for developing new laser systems for both, advanced atomic physics and dermatological applications, based on fibre technology.

Work performed

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 75ÂºC 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 Ã“ptica group from the Consejo Superior de Investigaciones CientÃficas (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.

Final results

In this project we contributed beyond the state of the art with the development of the first Single-frequency MOPA fibre laser with more than 2 Watts output power, and tunable in the 915-937nm window. Also, by second harmonic generation more than 400 mW of blue radiation was achieved. Along the last period of the project, tests for power scalability of the laser were carried out, achieving single-frequency operation up to 5 Watts. NeoLaS has also generated excellent results beyond the state of the art at other exotic wavelengths. For instance, we developed two high-power low-noise SF MOPA fibre lasers at 1013 nm and 1120 nm, with record output powers of 50W and 25W respectively. Also, we demonstrated a 1Watt all-fibered laser source at 852nm for focused ion beam (FIB) experiment based on cold Cesium atoms.
The international collaborations stablished within the framework of NeoLaS have led to the generation also of high impact results in the field of random distributed fibre lasers. We contributed to the understanding of noise processes by combining experimental and numerical simulations. We developed the first Watt-level random fibre and we delivered a prototype for testing in high resolution microscopy.
To summarize, the developments carried out in this project paved the way for new fibre continuous as well as pulsed sources that could be used in different applications such as atom cooling, metrology, sensing and medic applications among others. The collaboration in this project with industry leaves the door open for a future development of a commercial product.