177,208 research outputs found
Cooperative luminescence and absorption in Ytterbium-doped silica fiber and the fiber nonlinear transmission coefficient lambda=980 nm with a regard to the Ytterbium ion-pairs' effect: comment
No full textRecently, significant power losses in ytterbium-doped fibers have been interpreted as resulting from the formation of ytterbium ion pairs [A. V. Kir’yanov et al., Opt. Express 14, 3981 (2006)]. However, there appears to be strong evidence against this model
Sub-40-fs pulses with 18-W average power from a passively mode-locked thin disk Yb:YAG laser with nonlinear fiber compression
No full textBy combining a passively mode-locked high-power laser with a large mode area holey fiber for nonlinear compression, we generated 33-fs pulses with 18-W average power. The output beam is linearly polarized and close to diffraction-limited. ©2002 Optical Society of America.F. Brunner, T. Siidmeyer, E. Innerhofer, R Paschotta, U. Keller, K. Furusawa, J. C. Baggett, T. M. Monro, and D. J. Richardso
80 fs pulses from a stretched-pulse Yb<sup>3+</sup>:silica fibre laser
No full textWe report the first demonstration of ultrashort pulse generation in a Ytterbium:silica fibre laser. The self-starting, stretched-pulse laser system produces 100 pJ, transform-limited, 80 fs pulses and represents a key step in the development of an all-solid-state, Yb3+-based, high power amplified system
Infrared-induced photodarkening in Tm-doped fluoride fibres
No full textWe have observed a new type of infrared-induced photodarkening in high-numerical-aperture fluoride fibers doped with 3000 and 10,000 parts in 106 by weight of Tm. The loss induced in the visible region by 1140-nm radiation is very strong (as high as 25 dB in a 50-cm piece) and broadband it can be removed by irradiation with the same pump wavelength at lower powers
Thulium-doped upconversion fibre-laser with 230mW of 480nm blue output
No full textBlue laser sources are required for a number of applications such as colour displays, printing and data recording. Three main approaches are currently pursued. Blue emitting laser diodes have recently been demonstrated, albeit with a number of limitations at present regarding power lifetime and operating temperature. Another approach is frequency doubling of an infrared source; for example 49mW of 473nm light have recently been obtained by frequency doubling the output of a diode-pumped 946nm Nd:YAG laser in a single pass through a periodically poled LiNbO3 crystal. The third approach is upconversion lasing, for which the highest reported power to date, at blue wavelengths, was 106mW from a diode-pumped Tm:ZBLAN upconversion fibre laser. In this paper we report a blue output of up to 230mW, achieved by using a more powerful pump laser and a Tm:ZBLAN fibre with a modified composition, which has allowed higher power operation. Long term operation at the highest power is not yet possible however due to an optically induced loss in the fibre as observed in earlier work. The pump laser was a Nd:YAG laser operating at 1123nm and pumped by a 7W diode-bar. This laser produced 1.6W in a circular Gaussian-beam of M2 < 1.1. The high beam quality allowed overall launch efficiencies into the fibre of between 50 and 60%. The Tm-doped fibre used, produced by Le Verre Fluoré, had a Tm concentration of 1000ppm (by weight), a NA of 0.2, a core diameter of 3µm and length of 2.2m. To form the cavity, dielectric mirrors were dry butted against both ends of the fibre. The input mirror had high reflectivity for blue light, and a transmission of 90% for the 1123nm pump, which was launched through this mirror using an aspheric lens. The output coupler had a transmission of 37% for the blue. This laser had a threshold of 100mW of incident pump power, and a slope efficiency of 18.5%, again with respect to incident power. For high pump powers the slope efficiency rolled off, and the maximum output obtained was 230mW for 1.6W of incident power. It was noted that this output power could not be sustained. Instead, at a constant pump power, the output would gradually decrease to some sustainable level. Around 140mW was the highest sustainable power achieved. The underlying cause of this effect was an induced loss in the fibre at blue wavelengths, thus increasing the threshold and decreasing the slope efficiency. Further tests revealed that this loss is not permanent and it can be entirely removed by operation of the fibre laser at low powers for a time of the order of an hour. It is hoped that an understanding of the loss mechanism and its relation to material composition could lead to upconversion lasers with even higher sustainable powers
Characterization and modelling of thulium:ZBLAN blue upconversion fibre lasers
No full textWe have investigated the performance of blue upconversion fibre lasers based on thulium-doped ZBLAN fiber, operating at 480 nm with a 1140-nm pump. Extensive fluorescence measurements have provided the necessary spectroscopic data to present a computer model that he performance of such lasers with good accuracy despite the complicated three-step upconversion mechanism and the influence of ion-ion energy transfer processes. We have identified the mechanisms that populate the levels above the 1G4 level and are able to specify the corresponding spectroscopic parameters. We discuss the relevance of these processes to the 480nm laser performance. Furthermore, we have calculated optimized parameters for such lasers
Resonant loop mirror with narrow-band reflections and its applications in single-frequency fibre lasers
No full textWe present a new form of loop mirror (to be realized with all-fiber or integrated optics technology) that can produce narrow-band reflections and could find an application in single-frequency fiber lasers, allowing for a standing-wave design with a long doped section and eliminating the need for a Faraday isolator or a fiber grating. We discuss the main features of such a loop mirror and present experimental results that agree well with the theory
Improved blue laser results and photochromic effects in Tm:ZBLAN fibre
No full textUpconversion lasing in Thulium-doped fluoride fibre has proved to be an efficient method of upconverting infrared light into blue laser emission and has been identified as a promising method of producing a compact short wavelength laser. There remains considerable scope for optimisation of performance, and we have been able to improve on previously reported results. However, attempts at optimisation by going to higher dopant concentrations have revealed interesting and unexpected photochromic effects. Optimisation of the output coupling has produced a slope efficiency for blue lasing output with respect to absorbed infrared power of 34% in 1000ppm Tm-doped fibre. Further, a diffraction grating has been used as an external tuning element and tuning of the blue output over a wavelength range of 475 to 486 nm has been achieved. To date the best results have all been achieved with fibres of very similar parameters; 1000ppm Tm-doped, NA = 0.2, single mode cutoff at 800 nm. We have recently investigated the effect of increasing the Tm concentration and have encountered a number of unexpected results. In more heavily doped fibres, pumping the Tm absorption at 1.14 µm, the optimum wavelength for upconversion pumping, results in an induced fibre loss across the visible spectrum. While this loss appears stable at room temperature it can be reversed by pumping with a significantly lower power at the same wavelength. The spectrum of the induced loss has been measured from 0.4 to 1 µm and the peak loss is dependant on the inducing power but has been measured as high as 20 dB/m. Such a loss has serious implications for lasing performance. Continuing work is aimed at discovering the source of this photochromic loss
Ytterbium-doped fibre amplifiers
No full textThe ytterbium-doped fiber amplifier offers a number of attractive features, including a broad-gain bandwidth and a high efficiency, due in large part to its freedom from various competing processes seen in other rare-earth dopants. Here we discuss the main features that influence design and possible applications of ytterbium-doped fiber amplifiers
Characterization and computer modelling of thulium doped upconversion fibre lasers
No full textThe Thulium ion in a ZBLAN host is a promising candidate for the implementation of fibre lasers utilizing several different upconversion schemes. Very efficient 480 nm lasing at room temperature has already been demonstrated with 1120/1140 nm pumping at Amoco [1] and in our group [2] where some new fibres are currently under investigation. Optimization of the performance requires a quantitative understanding of the system, including degrading effects especially at higher dopant concentrations of up to 10,000 ppm. We have measured not only the laser performance but also the steady-state fluorescence and the fluorescence decay of Tm doped ZBLAN fibres for various pump wavelengths. A detailed computer model, including the three-step excitation scheme as well various energy transfer processes between excited ions, has been developed and brought into good agreement with the experimental data. In this way we have clearly identified several new energy transfer processes. They were found to limit the performance of the 480 nm transition from the 1G4 level, but at the same time they should provide enough population in the 1D2 level for lasing at 455 nm and perhaps even 365 nm with a single 1140 nm pump. Unfortunately, we have also found a broad-band absorption induced by the infrared pump light; this effect seems to depend strongly on the Tm3+ concentration. It prohibited lasing at the mentioned wavelengths so far, but it could well be absent in new fibres which may be available soon. In this paper we will provide details of the computer model, and highlight those processes which play an important role in the various upconversion laser schemes. Other groups have achieved efficient lasing at 1.47µm and 810nm by pumping similar fibres with 1064nm [3, 4] although the ground-state absorption is very weak at this pump wavelength. To understand this is another goal of our work which is still in progress
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