Efficient extraction of high pulse energy from partly quenched highly Er3+-doped fiber amplifiers

We demonstrate efficient pulse-energy extraction from a partly quenched erbium-doped aluminosilicate fiber amplifier. This has a high erbium concentration that allows for short devices with reduced nonlinear distortions but also results in partial quenching and thus significant unsaturable absorption, even though the fiber is still able to amplify. Although the quenching degrades the average-power efficiency, the pulse energy remains high, and our results point to an increasingly promising outcome for short pulses. Furthermore, unlike unquenched fibers, the conversion efficiency improves at low repetition rates, which we attribute to smaller relative energy loss to quenched ions at higher pulse energy. A short (2.6 m) cladding-pumped partly quenched Er-doped fiber with 95-dB/m 1530-nm peak absorption and saturation energy estimated to 85 µJ reached 0.8 mJ of output energy when seeded by 0.2-µs, 23-µJ pulses. Thus, according to our results, pulses can be amplified to high energy in short highly Er-doped fibers designed to reduce nonlinear distortions at the expense of average-power efficiency

Estimation and Management of Performance Limiting Factors in the Development of 1 kW Peak Power Pulsed Fiber MOPA at 1550 nm

An all-fiber three-stage master oscillator power amplifier (MOPA), based on Erbium and Erbium-Ytterbium co-doped fibers, has been designed and developed. The performance of such a laser is primarily limited by amplified spontaneous emission (ASE), Yb bottlenecking, and non-linear effects. Other important factors, that need to be considered towards performance improvement, are fiber bend diameter and heat generated in the fiber. This paper describes the methodology for the estimation and management of these limiting factors for each amplifier stage. The work presented here is limited to the fibers which are commercially easily available, unlike customised Yb- free large mode area (LMA) Erbium-doped fibers, where very high peak and average powers are being reported due to the absence of Yb ASE. Presented experimental results and discussion shall be beneficial for the fiber laser amplifier designers. With suitable management, 1 kW peak power pulses of 30 ns duration at 200 kHz repetition rate have been achieved with 30 % optical efficiency. The collimated output of 6 W average power (limited by Yb ASE) with high beam quality (M2 ≈ 1.6) at 1550 nm can be employed for a variety of applications. By adding additional amplifier stages, power can be scaled further

Compact and efficient sub-10 ps pump sources at 2 µm for the generation of coherent mid-infrared radiation

Ultrashort pulse laser systems in the 2 µm wavelength region featuring high pulse energies are powerful tools for driving a multitude of different applications in industry, medicine, and fundamental science. The implementation of such laser sources remains challenging and usually relies on the chirped-pulse amplification (CPA) in regenerative amplifiers. Here, a much more simplified concept based on a CPA-free multipass amplification scheme operating at room temperature has been investigated. I show that optical pulses with moderate sub-10 ps duration can be amplified up to the millijoule energy level without the onset of nonlinear effects in holmium-doped crystals. The laser system consists of an ultrafast all-fiber mode-locked oscillator and power amplifier based on holmium-doped silica fiber. It has been spectrally tailored to efficiently seed subsequent amplifiers based on holmium-doped YLiF4 crystals. A multipass amplification concept was used to amplify the nJ-level seed pulses from the fiber front-end up to 100 µJ of pulse energy at a pulse repetition frequency of 50 kHz. The maximum pulse energy was limited only by the laser-induced damage threshold of the amplifier crystals. Further pulse energy scaling has been achieved in a final single-pass booster amplifier generating 1.2 mJ at 1 kHz. The overall gain in the Ho:YLF crystals amounts to > 51 dB. Taking into account a measured pulse duration of 8.3 ps, this yields a pulse peak power of 136 MW. These results have been supported by numerical simulations based on a modified Frantz-Nodvik formalism, which is capable of modeling chromatic effects as well as a detailed description of the energy built-up in such amplifiers. Up to 50 µJ at 100 kHz from the multipass amplifier have been used to pump an optical parametric generator/amplifier tandem configuration based on the highly nonlinear non-oxide crystal ZnGeP2. The phase-matching condition has been set to achieve a signal and idler center wavelength of 3 µm and 6.5 µm, respectively. The maximum signal and idler pulse energy was 7.7 µJ and 2.5 µJ. Considering a measured pulse duration of 4 ps for both wavelengths, a peak intensity of about 2 MW (signal) and 0.5 MW (idler) was reached. The mid-IR coherent source is wavelength tunable covering the spectral range from 2.5 to 8 µm under appropriate phase-matching conditions and has shown long-term stability of less than 1.25%rms low-frequency power noise

Research and development of thulium-doped fibre lasers

A dissertation submitted to the Faculty of Science, University of the Witwatersrand, in fulfilment of the requirements for the degree Master of Science, 2017Three thulium-doped fibre lasers (TDFLs) were developed: a large mode area (LMA) 25/400 “test” TDFL, a high power cw TDFL, and a Q-switched TDFL. For the test TDFL, the relationship between self-pulsing in TDFLs and laser reabsorption effects were explored by way of spectral and temporal measurements. Laser design aspects and technical procedures were also investigated. The highly efficient, high power cw TDFL produced a pump limited output power of 63 W with a slope efficiency of ~56 %. Thermal management schemes including splicing and fibre cooling were discussed and implemented. A polarisation maintaining thulium-doped fibre (TDF) was implemented for the Q-switched TDFL which produced pulse lengths of ~207 ns and peak powers of 1.17 kW at ~23 W of average laser output power. Gain switching of the Q-switched TDFL pump diodes further reduced the output pulse length to ~163 ns with peak powers of 1.35 kW.XL201

Effect of processing on the structure and properties of glasses and glass-ceramics for photonic applications

Tesis Doctoral inédita leída en la Universidad Autónoma de Madrid, Facultad de Ciencias, Departamento de Física de Materiales. Fecha de lectura: 29-04-2019Esta tesis doctoral ha sido realizada en el Departamento de Vidrios del Instituto de Cerámica y Vidrio (ICV-CSIC) y desarrollada en el marco de los proyectos MAT2013- 48246-C2-1-P/2-P y MAT2017-87035-C2-1-P/-2-P(AEI/FEDER,UE). La estancia en el “Laboratory of Optical Fibre Technology” de la Universidad de Bialystok (Polonia) ha sido financiada por el COST Action: MP140

Synthèse, caractérisation et modélisation de matériaux en couches minces pour l’optique en vue d’applications

Les travaux réalisés ces dernières années m’ont amené à combiner ces trois aspects : synthèse de matériaux, caractérisations et modélisation. A propos de la synthèse de matériau, j’ai utilisé la synthèse par voie chimique pendant ma thèse (film mince de PZT) et mon postdoc (film mince polymère). A Caen, les méthodes de synthèse utilisées sont des méthodes physiques comme la pulvérisation cathodique magnétron. Mes activités directes sont actuellement plus centrées sur la caractérisation et la modélisation des matériaux optiques, réalisés au sein de l’équipe NIMPH ou étudiés par l’intermédiaire de collaborations. Dans la suite du manuscrit, je vais détailler les travaux post-doctoraux expérimentaux et théoriques réalisés en Suède, à Caen et en collaboration avec des laboratoires partenaires. Certains sujets ayant fait l’objet de publications détaillées seront brièvement abordés d’autres sujets ayant fait l’objet de moins de publications seront plus densément développés

Advanced Photonic Sciences

The new emerging field of photonics has significantly attracted the interest of many societies, professionals and researchers around the world. The great importance of this field is due to its applicability and possible utilization in almost all scientific and industrial areas. This book presents some advanced research topics in photonics. It consists of 16 chapters organized into three sections: Integrated Photonics, Photonic Materials and Photonic Applications. It can be said that this book is a good contribution for paving the way for further innovations in photonic technology. The chapters have been written and reviewed by well-experienced researchers in their fields. In their contributions they demonstrated the most profound knowledge and expertise for interested individuals in this expanding field. The book will be a good reference for experienced professionals, academics and researchers as well as young researchers only starting their carrier in this field

Rate equation analysis of nanocrystal-enhanced upconversion in neodymium-doped glasses

Das Wachsen von hexagonalen BaCl2-Nanokristallen in Fluorozirkonatbasierten Gläsern führt zu einer drastischen Steigerung der Photolumineszenz des darin eingebetteten Neodyms. Ein Ratengleichungssystem wird entwickelt, um die Anregungs- und Relaxationsdynamik auf ein Modell abzubilden. Die durch die Nanokristalle bedingten Verstärkungsmechanismen werden hinsichtlich ihres Einflusses auf die Hochkonversion von nahinfraroten Photonen in den sichtbaren Spektralbereich analysiert. Nachdem die korrekte Beschreibung der Stokes- und Anti-Stokes-Prozesse mittels verschiedener selektiver Experimente nachgewiesen ist, wird das Modell dazu genutzt, um eine Vorhersage für die Nutzbarkeit einer hochkonvertierenden Schicht unter einer bifazialen Solarzelle zu machen. Ein solches System kann genutzt werden, um den nahinfraroten Anteil des Sonnenlichts, der gewöhnlich durch eine Solarzelle durchgelassen wird, zu Wellenlängen zu konvertieren, die zur photoelektrischen Konversion beitragen können. Es stellt sich heraus, dass insbesondere neodym-dotierte Gläser und Glaskeramiken als hochkonvertierende Schichten interessant sein könnten, da die elektronische Struktur von Neodymium eine breitbandige Absorption des nahinfraroten Sonnenlichts ermöglicht.A remarkable increase of photoluminescence from neodymium arises from the growth of hexagonal BaCl2 nanocrystals in fluorozirconate-based glasses. A rate equation model is introduced to describe the excitation and relaxation dynamics in this material system comprehensively. The enhancement mechanisms due to the nanocrystals are analysed with a focus on their impact on the upconversion of near-infrared photons to the visible spectral range. After validating the description of Stokes and Anti-Stokes processes with a range of selective experiments considering the time-, power- and concentration dependence, the model is used to make a prediction on the feasibility of an upconverting bottom-layer below a bifacial solar cell. Such device may be used to convert the near-infrared fraction of the solar spectrum transmitted by a silicon solar cell to wavelengths that can contribute to the photoelectric conversion. Neodymium-doped glasses and glass ceramics turn out to be particularly interesting upconverting layers because of neodymium’s electronic structure that allows for a broadband absorption of the solar near-infrared.von Ulrich Skrzypcza