Ytterbium-doped glass regenerative chirped-pulse amplifier

doi:10.1016/S0030-4018(98)00626-9

Optics Communications

Volume 160, Issues 1–3, 1 February 1999, Pages 92-97

https://doi.org/10.1016/S0030-4018(98)00626-9 Get rights and content

Abstract

Chirped-pulse amplification in a Yb³⁺-doped phosphate glass regenerative amplifier pumped by a free-running Ti:sapphire laser is demonstrated. Amplified chirped pulse energies up to 20 mJ were obtained. Amplified bandwidths of 20 nm at reduced energies were obtained using regenerative spectral shaping. Spectroscopic measurements are presented which are necessary to model amplification in a quasi-three-level laser.

Introduction

Currently, Ti:sapphire is the material of choice for ultrashort-pulse (<50 fs), high-average-power applications due to its large gain bandwidth and excellent thermal properties. Ti:sapphire would be the optimal material for the generation of high-intensity pulses, except for its short lifetime (3 μs) and location of absorption band (400–600 nm) which result in difficulties in producing simple pump sources. For high energy (>5 J) applications, Nd:glass chirped-pulse-amplification (CPA) 1, 2laser systems are utilized. The ability to flashlamp pump and fabricate large size Nd:glass, makes it easy to store high energies. However, the bandwidth of Nd:glass limits the final compressed pulse to 300 fs at best [3]and poor thermal properties limit the average power to 1 W [4].

Largely due to its ability to be directly diode pumped and its small quantum defect, ytterbium-doped materials have recently generated a heightened interest (for example, Refs. 5, 6). Yb:glass is a promising ultrashort-pulse material with numerous attractive properties which can reduce the complexity and size of high-peak-power CPA systems [7]. The broad fluorescence spectrum provides sufficient bandwidth to generate and amplify ultrashort pulses, with a 60-fs pulse duration thus far obtained from a modelocked Yb:glass laser [8]. The millisecond upper-state lifetime permits simple pump sources such as free-running lasers and laser diodes. The simple electronic energy level structure (shown in Fig. 1) results in a small quantum defect (<9%) and high-doping concentrations (>10²¹/cm³) due to the absence of quenching, excited-state, and up-conversion processes. The small quantum defect reduces the heat load in the Yb:glass. The high doping concentration allows for thin disk geometries for the gain medium which are advantageous for cooling and reduction of the B-integral. The location of the absorption band (900–1000 nm) is suited for pumping with InGaAs laser diodes. The relatively high saturation fluence (40–80 J/cm²) of Yb:phosphate glass combined with the high doping density and long upper-state lifetime, results in a gain medium which can easily store an extremely high energy density. While the high saturation fluence is an advantage for storing energy, it presents a challenge for extracting the energy, as a consequence of the relatively low emission cross-section. The problem is addressed by using a low-gain low-loss regenerative amplifier to efficiently extract the stored energy [9]. The inversion in such an amplifier is gradually depleted in many round trips without reaching the saturation fluence, thus allowing for efficient energy extraction while avoiding damage.

In this paper, spectroscopic measurements are first presented and challenges of making such measurements in the quasi-three-level system of the Yb³⁺ are discussed. Experimental results are presented of a Yb³⁺-doped glass regenerative amplifier producing amplified bandwidths ranging from 7 to 20 nm, and amplified pulse energies ranging from 20 to 7 mJ.

Section snippets

Spectroscopy

The emission cross-section spectrum, σ_e(λ), the absorption cross-section spectrum, σ_a(λ), and the upper-state lifetime, τ, are fundamental properties of amplifier medium which need to be determined in order to model and design the amplifier. In particular for quasi-three-level CPA, knowledge of the gain spectrum is essential to maximize the pulse energy and amplified bandwidth. Ytterbium-doped phosphate glass (Kigre QX/Yb) with a doping concentration of 15 wt.% of Yb₂O₃ was used for this

Laser experiments

The pump source for these experiments was a tunable flashlamp-pumped Ti:sapphire laser (Elight) which could produce 200 mJ at 10 Hz in the range of 900–950 nm. The pump laser cavity simply consisted of an end mirror, output coupler, tuning prism, and the Ti:sapphire rod. The temporal profile of the pump pulse consisted of six relaxation oscillations with an entire duration of approximately 5 μs. First, a gain-switched Yb:glass laser was constructed in order to determine possible efficiencies. A

Conclusions and future directions

The regenerative amplifier provides a means of efficient CPA in a gain material with a saturation fluence greater than the damage threshold. Further optimization of the efficiency is possible by reducing the intracavity losses and improving the mode-matching between the pump and amplified pulse. From the simulation, if the losses are reduced to 5% in a single pass, an extraction efficiency of 20% is obtainable. The emission and absorption cross-section spectra represent the starting point for

Acknowledgements

The authors are grateful to Kigre, Inc. for providing Yb:glass samples, Elight Laser Systems for supplying the Ti:sapphire pump laser, and to Marcel Bouvier of Medox for adapting the Pockels cell driver for our regenerative amplifier. Subrat Biswal thanks Kim Winick of the University of Michigan and Falgun Patel of Lawrence Livermore National Laboratory for useful discussions regarding the spectroscopic measurements.

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Optical properties of Yb3+-doped phosphate laser glasses
2011, Journal of Alloys and Compounds
Citation Excerpt :
Since the τ0 of the Yb3+ donor ions in the absence of acceptors is around 1037 μs, then the decay of the luminescence from any excited level can be described by a single exponential, i.e., τexp = τR. The multiphonon relaxation probability WMPR can be neglected as it needs 9 phonons to bridge the large energy gap of around 10770 cm−1 between the 2F5/2 and the 2F7/2 levels [46] in phosphate glasses [47]. As there is no intermediate level for the Yb3+ ion, the energy transfer between Yb3+ ions due to cross-relaxation process do not exist.
Ytterbium-doped phosphate glasses have been prepared and studied their spectroscopic properties through absorption, emission and Fourier transform infrared (FTIR) spectral studies and time-resolved luminescence decay curves. The absorption cross-section has been found to vary with the variation of Yb₂O₃ concentration. The results of the FTIR spectra show that the OH⁻ content is increasing with increase of the Yb₂O₃ concentration in these glasses. The decay curves of the ²F_5/2 level of Yb³⁺ ions exhibit a single exponential nature for all the concentrations. The lifetimes of the ²F_5/2 level of Yb³⁺ ions decreases from 1.04 to 0.27 ms when the Yb₂O₃ concentration is increased from 0.1 to 6.0 mol%. The quenching of lifetimes has been found to vary directly with the inter-ionic distance between the Yb³⁺ ions. The concentration quenching of the lifetime has been analyzed using different energy transfer processes and no evidence of cooperative luminescence of Yb³⁺ ions has been found in these glasses, which reveals that the present glasses are useful for photonic device applications. The laser performance properties have also been evaluated for these glasses and compared with those of other reported Yb³⁺-doped glass systems.
Optical properties of glasses (TeO<inf>2</inf>-GeO<inf>2</inf>-K<inf>2</inf>O) thin films co-doped with rare earth oxides Sm<inf>2</inf>O<inf>3</inf>/Yb<inf>2</inf>O<inf>3</inf>
2009, Journal of Alloys and Compounds
Glassy thin films of [TeO₂–GeO₂–K₂O] co-doped with rare earth oxides Sm₂O₃/Yb₂O₃ were prepared by electron beam evaporation technique on polished fused silica glass substrate. The effect of Sm₂O₃/Yb₂O₃ rare earth sub-oxides co-doping on optical properties of glasses 80TeO₂–10GeO₂–8K₂O thin films has been investigated using optical spectrophotometry measurements in the wavelength range 200–2500 nm. The structural characteristics studied by X-ray diffraction (XRD) showed that all the films are amorphous. The fundamental optical parameters like band gap and absorption coefficient are calculated in the strong absorption region of transmittance and reflectance spectrum. The possible optical transition in these films is found to be allowed indirect transition with energy gap $E_{g}^{opt}$ decreases from 1.27 to 1.06 eV with increasing Yb₂O₃ at expense of Sm₂O₃. The decreasing in $E_{g}^{opt}$ can be interpreted in terms of the non-stoichiometry of the films. The refractive indices have been evaluated in term of envelope method suggested by Swanepoel in the transparent region. The refractive index, n, can be extrapolated by Cauchy dispersion relationship over the whole spectra range. It is observed that the refractive index, n increases with increasing Yb₂O₃ at expense of Sm₂O₃ which might be related to the changes in the compositions of TeO₂ and GeO₂ sub-oxides in the films.
Influences of Yb3+ ion concentration on the spectroscopic properties of silica glass
2008, Journal of Non-Crystalline Solids
We investigated optical spectroscopic properties of silica glass doped with ytterbium (Yb³⁺) ions to assess their lasing performance in diode-laser pumped systems. The Yb-doped silica glass preforms were fabricated by solution doping technique using the MCVD process. The stimulated emission cross-section and laser performance parameters were determined from the measured absorption spectra using the method of reciprocity. Fluorescence decay characteristics were observed to be deviated from exponential behavior as the Yb³⁺ ions doping level increases and there exists a lifetime quenching behavior related to the cluster effect of Yb³⁺ ions into silica glass. Nevertheless, lasing parameters indicated that clustering of Yb³⁺ ions does not significantly affect the spectral properties relevant to the predicted lasing performance when concentration is low, but becomes predominant at higher concentration.
Effect of F- ions on emission cross-section and fluorescence lifetime of Yb3+-doped tellurite glasses
2005, Journal of Non-Crystalline Solids
The effects of F⁻ ions in Yb³⁺-doped tellurite glass systems on the emission cross-section and measured fluorescence lifetime are investigated. The results show that both the emission cross-section and the fluorescence lifetime of Yb³⁺ ions increase from 1.32 to 1.39 pm² and from 0.93 to 1.12 ms respectively with the increase of F⁻ ions from 0 to 10 mol% and that such oxyfluoride tellurite glass system is a promising laser host matrix for high power generation. FT-IR spectra were used to analyze the effect of F⁻ ions on the structure of tellurite glasses and the change of OH⁻ groups in this glass system. Analysis demonstrates that the addition of fluoride decreases the symmetry of the structure of tellurite glasses resulting in increasing of the emission cross-section and removes the OH⁻ groups resulting in increasing of the measured fluorescence lifetime of Yb³⁺ ions.
Thermal analyses, spectral characterization and structural interpretation of Yb3+ doped TeO<inf>2</inf>-ZnO-ZnCl<inf>2</inf> glasses
2005, Physics Letters, Section A: General, Atomic and Solid State Physics
Citation Excerpt :
The Yb3+ ion is of interest in lasers for the next generation nuclear fusion and as a sensitizer of energy transfer for infrared to visible upconversion and infrared lasers [1].
Bulk glasses have been prepared in the TeO₂–ZnO–ZnCl₂ systems. Their characteristic temperatures were determined and analyzed. Raman and FT–IR spectra were used to analyze the effect of ZnCl₂ on the structure and spectral properties of tellurite glasses and OH⁻ groups in this glass system. The spectroscopic properties including absorption spectra, emission cross-sections and fluorescence lifetimes of Yb³⁺ in TeO₂–ZnO–ZnCl₂ were measured and calculated. It is demonstrated that the progressive replacement less than 20 mol% of TeO₂ by ZnCl₂ improves the thermal stability, removes the OH⁻ groups, turns TeO₄ bi-pyramidal arrangement into TeO₃ (and/or TeO₃₊₁) trigonal pyramids structures and results in the decrease of the symmetry of the structure, which increases the emission cross-sections and lifetimes. But when the content of ZnCl₂ up to 30 mol%, the glass system becomes more hygroscopic and introduces more OH⁻ groups, which decrease the emission cross-sections and shorten the lifetimes. The results show that the glass system with 69TeO₂–10ZnO–20ZnCl₂–1Yb₂O₃ is a desirable component for active laser media for high power generation.
Effect of F- ions on spectroscopic properties of Yb 3+-doped zinc-tellurite glasses
2005, Journal of Physics and Chemistry of Solids
This article has been retracted at the request of the Editors, after a reader brought the following to their attention.
Reason: The article substantially reproduces parts of articles published by the same authors in the Journal of Luminescence (“Effect of F⁻ ions on physical and spectroscopic properties of Yb³⁺-doped TeO₂ glasses”, Volume 113, Issues 1–2, Pages 27–32) and the Journal of Alloys and Compounds (“Fluorescence lifetime increase by introduction of F⁻ ions in ytterbium-doped TeO₂-based glasses”, Volume 393, Issues 1–2, Pages 279–282). There was also a failure to cite either of these articles. These other articles have also been retracted.
This action has been agreed by the Editors of the three journals.

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Optics Communications

Abstract

Introduction

Section snippets

Spectroscopy

Laser experiments

Conclusions and future directions

Acknowledgements

References (18)

Opt. Commun.

IEEE J. Quantum Electron.

J. Opt. Soc. Am. B

IEEE J. Quantum Electron.

IEEE J. Sel. Top. Quantum Electron.

IEEE J. Sel. Top. Quantum Electron.

IEEE J. Sel. Top. Quantum Electron.

Opt. Lett.

IEEE J. Sel. Top. Quantum Electron.

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Optical properties of Yb<sup>3+</sup>-doped phosphate laser glasses

Optical properties of glasses (TeO<inf>2</inf>-GeO<inf>2</inf>-K<inf>2</inf>O) thin films co-doped with rare earth oxides Sm<inf>2</inf>O<inf>3</inf>/Yb<inf>2</inf>O<inf>3</inf>

Influences of Yb<sup>3+</sup> ion concentration on the spectroscopic properties of silica glass

Effect of F<sup>-</sup> ions on emission cross-section and fluorescence lifetime of Yb<sup>3+</sup>-doped tellurite glasses

Thermal analyses, spectral characterization and structural interpretation of Yb<sup>3+</sup> doped TeO<inf>2</inf>-ZnO-ZnCl<inf>2</inf> glasses

Effect of F<sup>-</sup> ions on spectroscopic properties of Yb <sup>3+</sup>-doped zinc-tellurite glasses