A monolithic thulium doped single mode fiber laser with 1.5ns pulsewidth and 8kW peak power

Abstract

Here we report a compact monolithic 2000nm pulsed laser with a single spatial mode output, ~1.5ns pulse duration, 8kW peak power and >200mW average power at 20 kHz repetition rate. The gain-switched laser, consisting of a pair of fiber Bragg gratings and 0.5m of thulium-doped single cladding fiber, was core pumped by a high peak power pulsed 1.5μm laser. When the input pulse energy of the 20 kHz pump pulses was sufficient enough to saturate the Thulium doped fiber, a stable 20 kHz pulse train was observed with measured linewidth of 0.05nm which corresponds to the limit of resolution for the Optical Spectrum Analyzer. This compact, pulsed 2000 nm laser, to the authors' limited knowledge, represents the first Tm-doped fiber laser with 8kW peak power and several ns pulse duration; which is less than the previously reported tens of ns pulsewidth previously reported from gain-switched Tm-doped fiber lasers.

Temporal characteristics of in-band-pumped gain-switched thulium-doped fiber lasers

“…This phenomenon can be related to the different experimental observations mentioned in Section 1. Jiang and Tayebati [1] observed the trailing spike phenomenon, but Ding et al [11] did not. This was because the former study used a 100-ns pump source, while the latter employed a pump source with a pulse width of only 2-3 ns.…”

“…This means there are other mechanisms related to this phenomenon. Besides, in the experiment of Ding et al [11], from which a record 1.5-ns pulse width of the in-band-pumped GSTDFLs was achieved, the authors did not detect the trailing spike phenomenon even when the laser pulse stopped growing as the pump power increased. Since the main difference between the two experiments mentioned above was that they used pump sources with different pulse widths and peak power, the relation between the pump source and the trailing spike phenomenon seems obvious.…”

Temporal characteristics of gain-switched thulium-doped fiber laser near threshold

“…However, when these gain-switched TDFLs are pumped around 790 nm or 1 μm, the output pulses consist of a series of unstable chaotic relaxation spikes as the result of the long relaxation time (>10 μs) from the pump energy level to the laser emission 2 μm band [12,13]. Consequently, in order to eliminate the cross-relaxation processes and obtain stable output pulses, a resonantly pumped scheme by pumping these TDFLs in the 1.5 μm band has been put forward [15,16]. In this scheme, the population of the upper energy level can be built up instantaneously following the pump pulse, which is critical for single stable pulse generation.…”

Gain-switched all-fiber laser with narrow bandwidth

“…One downside of gain-switching is that the full capacity of the pump lasers is not utilized due to the pulsed pumping. Gain-switching is studied the most in Tmdoped lasers [9,10,13] but it has also been demonstrated in Nd-doped [14], Ho-doped [15], and Yb-doped fiber lasers [11,[16][17][18].…”

“…In terms of optical components a gain-switched fiber laser only requires the same components as an all-fiber CW laser, which makes it simple and cost-effective. Output pulse energies are typically in the tens to hundreds of microjoule range and with nanosecond pulse duration [9][10][11]. An example of an application is within supercontinuum generation [11], where the increased peak power reduces the dependence on the zero dispersion wavelength [12].…”