10 µJ 150 fs All-Fiber Yb Laser Amplifier System
¨Onder Akc¸aalan1, Hamit Kalaycıo˘glu1, Denizhan Koray Kesim2, F. ¨Omer Ilday1,2
1Department of Physics, Bilkent University, Ankara, 06800, Turkey
2Department of Electrical and Electronics Engineering, Bilkent University, Ankara, 06800, Turkey
Femtosecond laser pulse sources have become increasingly popular in the last decade as a result of their prac-tical features, such as insensitivity to environmental variations, versatile designs, high-power outputs. However, much of the progress is with non-integrated specialty fibers, which involve some compromise on these practical features. Monolithic fiber chirped pulse amplification (CPA) systems are very attractive for industrial and scientific applications due to the features such as compactness, reliability and robustness [1].
Here, we present a monolithic fiber optic CPA system built by commercially available components and
demon-strate 10 µJ pulses compressible to 150 fs duration for the first time, to our knowledge. Experimental setup is
shown in Fig. 1(a). The system seed source is a 60-MHz all-normal-dispersion modelocked fiber oscillator. The oscillator has a 10-nm (FWHM) spectrum, shown in Fig. 1(c). Oscillator output power is 50 mW. After the oscillator, rest of the system is built of polarization maintaining (PM) components. A single-mode preamplifier after the oscillator is employed to control both dispersion and nonlinearity in the amplifier system. The pulses are stretched with a 100 m-long fiber after the first pre-amplifier. The signal is amplified again by a second single-mode pre-amplifier before repetition rate is reduced via an acousto-optic modulator (AOM) to 220 kHz. Finally, a forward-pumped double-clad power amplifier, built of PM 20/125 Yb 1200 DC (nLight) fiber and pumped by a 18-W wavelength stabilized diode, boosts the optical power up to 2.2 W. To compress the pulses, a pair of 900 line/mm transmission gratings are preferred to denser gratings to limit third order dispersion (TOD). Further, fiber lengths are shortened as much as possible to minimize nonlinear effects and thus the power conversion efficiency is relatively low, around 30% for the power amplifier. The autocorrelation measurement for the compressed pulses indicate a width of ∼150 fs (Fig. 1(b)). The amplified output spectrum of FWHM of 14 nm is shown in Fig. 1(d).
Hence, a record compressed pulse duration is obtained for all-fiber amplifiers for amplified pulses of 10µJ.
PM Isolator PM WDM 80 cm. PM Yb fiber PM 95/5 Coupler 100 m. PM Stretch Fiber 5% Monitor Port SM Pump Diode 80 cm. PM Yb fiber PM WDM PM AOM PM 99/1 Coupler High Power PM Isolator 1% Monitor Port High Power Pump Diode SM Pump Diode 60 MHz ANDi Oscillator DC PM Yb Gain Fiber 80 cm. Angle Cleaved Fiber Tip PM Pump Combiner 10x Coated Lens High Power Free Space Isolator Movable Stage Mirror Mirror 900 line/mm transmission gratings Mirror Output
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Delay (ps)Intensity (a.u.)
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Fig. 1 (a) The monolithic fiber optic CPA system setup. (b) Compressed output pulse from gratings. (c) The oscillator spectrum. (d) The amplified output spectrum.
References
[1] D. J. Richardson, J. Nilsson, and W. A. Clarkson, “High power fiber lasers: current status and future perspectives,” J. Opt. Soc. Am. B 27, B63 (2010).
