Yb:YAG single crystal fiber power amplifier for femtosecond sources

Abstract : We demonstrate a versatile femtosecond power amplifier using a Yb:YAG single crystal fiber operating from 10 kHz to 10 MHz. For a total pump power of 75 W, up to 30 W is generated from the double-pass power amplifier. At a repetition rate of 10 kHz, an output energy of 1 mJ is obtained after recompression. In this configuration, the pulse duration is 380 fs, corresponding to a peak power of 2.2 GW. The M 2 beam quality factor is better than 1.1 for investigated parameters. Ultrafast lasers are now a common tool for scientific and industrial applications. Over the past decade, many technological developments of diode-pumped solid-state laser systems have allowed tremendous improvements of their performance, reliability, and cost. In order to achieve high energy per pulse in the femtosecond regime, master oscillator power amplifier systems are commonly used. Regenerative amplifiers based on bulk or thin disk Yb-doped crystals can amplify ultrashort pulses to several tens of millijoules [1,2]. They can provide high gain and high output energy at a low repetition rate, but they are limited in terms of repetition rate to a few hundreds of kilohertz due to the high-voltage-driven switch speed. Ytterbium-doped optical fibers can also be used to amplify ultrashort pulses. Their high surface-to-volume ratio provides good thermal management and allows attainment of high average powers of several hundreds of watts [3]. However, the signal confinement in small-cross-section cores induces nonlinear effects, such as self-phase modulation and self-focusing, which limit the peak power and the pulse energy. Femtosecond pulses with an energy of 2.2 mJ were obtained using the well-known chirped pulse amplification technique together with large-core-diameter photonic crystal fibers [4]. Another approach consists in amplifying femtose-cond pulses directly in Yb-doped crystals using multipass amplifiers without active elements. Although it requires quite complex systems, the slab geometry has proven to be a very successful approach. Up to 1.1 kW [5] average power and 20 mJ [6] energy were obtained with an Yb:YAG Innoslab amplifier. Significant improvement of the emission cross section and the thermal conductivity can be observed at cryogenic temperatures in most Yb-doped crystals. 40 mJ output energy was obtained using a cryogenic Yb:YAG double-pass amplifier [7]. However, stronger spectral narrowing at low temperatures induces longer optical pulses of several picoseconds. Finally, the single crystal fiber (SCF) concept lies between fibers and crystals and can contribute to original performance for femtosecond systems. SCFs are long, thin crystal rods with a diameter lower than 1 mm and a typical length of a few centimeters. SCFs are designed for free-space propagation of the laser signal, as in bulk lasers together with a guidance of the pump beam, which depends on the pump brightness. This concept has recently been successfully implemented in Yb:YAG lasers and demonstrated continuous emission of 250 W from an oscillator based on a 1% doped Yb:YAG SCF pumped by a 600 W laser diode [8]. This clearly shows the potential of this approach for high-power extraction. Furthermore, Yb:YAG SCF also demonstrated high single-pass gain with very simple amplifier geometries. In the context of ultrashort pulse amplification, SCF provides several advantages that clearly benefit the amplification of ultrashort and intense pulses. Among them, the mitigation of nonlinear effects thanks to the short length of interaction together with the large beam diameter is probably the most interesting. Also, the high gain per pass prevents the use of a regenerative amplifier and therefore significantly expands the range of operation at a high repetition rate. Consequently, Yb:YAG SCF has attracted attention as a potential simple, robust, and cost effective amplifier of ultrashort pulses. In a proof-of-principle experiment, femtosecond pulses were directly amplified from 400 mW to 12 W average power in a double-pass architecture while maintaining the duration of the 30 MHz repetition rate pulses below 400 fs [9]. In this Letter, we demonstrate a femtosecond power amplifier using a diode-pumped Yb:YAG SCF operating from 10 kHz to 10 MHz. For a total pump power of 75 W out of a fiber-coupled high-brightness laser diode, up to 30 W is generated from the double-pass power amplifier. At a repetition rate of 10 kHz, an output energy of 1 mJ is obtained after recompression. The experimental setup is shown in Fig. 1. The seed source provides a train of stretched and amplified pulses with a repetition rate ranging from 10 kHz to 10 MHz, a maximum energy per pulse of 150 μJ, and a maximum average power of 10 W. The optical spectrum is 4.3 nm at full width at half-maximum (FWHM) and is centered around 1030 nm to match the gain bandwidth of the Yb:YAG SCF booster placed downstream after optical isolation. A 500 mm focal length lens (L1) is used to focus
Type de document :
Article dans une revue
Optics Letters, Optical Society of America, 2013, 38 (2), pp.109-111. 〈10.1364/OL.38.000109〉
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Soumis le : lundi 18 avril 2016 - 11:34:01
Dernière modification le : jeudi 11 janvier 2018 - 06:26:34

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Xavier Delen, Yoann Zaouter, Igor Martial, Nicolas Aubry, Julien Didierjean, et al.. Yb:YAG single crystal fiber power amplifier for femtosecond sources. Optics Letters, Optical Society of America, 2013, 38 (2), pp.109-111. 〈10.1364/OL.38.000109〉. 〈hal-01303505〉

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