High average power (500W/50ps) and high peak power (3.2 MW/50ps) picosecond pulsed MOPA system with tapered double-clad ytterbium fiber

Abstract

In this study we demonstrate high power master oscillator power amplifier (MOPA) laser system delivering 50 ps pulses and capable to work in wide range of repetition rates. The gain-switched (GS) fiber coupled diode is used as a seed source to provide microwatt power level pulses at 1039.5 nm with FWHM 50 ps duration at a repetition rate in the range of 1 to 20 MHz. The maximum achieved amplified average power at 20 MHz repetition rate was measured to be 513 W corresponding to 481.9 kW of peak power and 25.7 µJ pulse energy. The gain of high-power amplifier reached over 44 dB with around 69% slope efficiency. Almost all optical power (<97%) was enclosed in the pulsed signal. In contrast, with repetition rate decreasing, the part of the optical power contained in the pulsed signal began to decrease, which directly follows from the spectra. The fraction of signal radiation decreased to about 50 % at maximum achieved power of 338.9 W at a repetition rate of 1 MHz. The peak power and the pulse energy in this case may be estimated as 3.2 MW and 169.5 µJ (in the limits of signal spectral bandwidth) respectively and corresponds to over 52 dB of gain with 60 % slope efficiency. The pulse duration changed insignificantly during amplification. Herewith advantages of polarization maintaining tapered double-clad optical fiber (PM-T-DCF) having near single mode input core diameters were allowed to maintain modal content during amplification and preserve near single mode output without significant deterioration