Efficient double-clad thulium-doped fiber laser with a ring cavity

Intensity-noise suppression in 1950-nm single-frequency fiber laser by bidirectional amplifier configuration

In this Letter, a bidirectional amplifier configuration suppressing the relative intensity noise in a 1950-nm linearly polarized single-frequency fiber laser (SFFL) is proposed. The scheme to amplify the signal in a nonlinear saturated amplification regime with low gain distribution for suppressing the RIN is theoretically analyzed. By optimizing the input power level and reflectivity of the bidirectional power-amplifier, the RIN is decreased maximally by >24dB within the frequency range of 200 kHz. A stable output power of over 5.16 W with a polarization extinction ratio of 21.2 dB is obtained. Additionally, the amplified signal maintains a linewidth of 7.1 kHz nearly identical with that of the seed, both with a signal-to-noise ratio of more than 60 dB. This all-optical technique on noise suppression applied to the fiber amplifier paves the way to realize low-noise SFFL with power improvement.

Developing high-power hybrid resonant gain-switched thulium fiber lasers

In this paper, we propose hybrid-pumped resonant gain-switched thulium fiber lasers to realize high-average-power and high-pulse-energy 2-μm laser emissions. Based on numerical simulation, laser dynamics (pulse peak power, pulse energy, pulse duration, etc.) of this kind of laser system are investigated in detail. By taking advantages of the 793 nm continuous wave pump and the 1900 nm pulsed pump, performance of the laser emission can be significantly improved, with the highest average power of 28 W, peak power of 3.5 kW, pulse energy of 281 μJ, and narrowest pulse duration of 92 ns, all of which can be further optimized through designing the cavity parameters and the pumping circumstance. Compared with the pump pulses, two times improvement in pulse energy and average power has been achieved. This hybrid resonant gain-switched system has an all-fiber configuration and high efficiency (low heat load), and can be steadily extended into the cladding pump scheme, thus paving a new way to realize high power (>100 W average power) and high pulse energy (>1 mJ) 2 μm thulium fiber lasers.

1590-nm-pumped passively Q-switched thulium all-fiber laser at 1900 nm

We propose and demonstrate a passively Q-switched 1900-nm thulium all-fiber laser using the mode-field-area mismatch method. A thulium fiber laser was core-pumped at 1590 nm and saturable-absorber Q-switched at 1900 nm through the use of a thulium saturable absorber fiber that had a relatively smaller mode field area than the gain medium. Sequential pulsing with a pulse energy of 12 μJ and a pulse duration of 160 ns was obtained. The pulse repetition rate was increased linearly with the applied pump power. With a pump power of 4.5 W, an average output power of 0.61 W and a pulse repetition rate of 50.7 kHz were achieved.

3.7 W fluoride glass Raman fiber laser operating at 2231 nm

The first demonstration of a multi-watt continuous wave fluoride glass Raman fiber laser operating beyond 2.2 μm is reported. A maximum output power of 3.7 W was obtained from a nested cavity setup with a laser slope efficiency of 15% with respect to the launched pump power.

High-power gain-switched Tm(3+)-doped fiber laser

Gain-switched by a 1.914-µm Tm:YLF crystal laser, a two-stage Tm(3+) fiber laser has been achieved 100-W level ~2-µm pulsed laser output with a slope efficiency of ~52%. With the 6-m length of Tm fiber, the laser wavelength was centered at 2020 nm with a bandwidth of ~25 nm. Based on an acousto-optic switch, the pulse repetition rate can be modulated from 500 Hz to 50 kHz, and the laser pulse width can be tuned between 75 ns and ~1 µs. The maximum pulse energy was over 10 mJ, and the maximum pulse peak power was 138 kW. By using the fiber-coiling-induced mode-filtering effect, laser beam quality of M2 = 1.01 was obtained. Further scaling the pulse energy and average power from such kind of gain-switched fiber lasers was also discussed.

Efficiency dependence on the Tm3+ and Al3+ concentrations for Tm3+-doped silica double-clad fiber lasers

We present measurements of the slope efficiency and the pump power at threshold for a number of Tm3+-doped silica double-clad fiber lasers that incorporate fibers that have a range of Tm3+ concentrations. We obtain a slope efficiency for the approximately 2-microm 3H4 --> 3H6 laser transition that is greater than the Stokes efficiency limit for a Tm3+ concentration as low as 1.3 wt. %. These results indicate that the cross relaxation process, 3F4, 3H6 --> 3H4, 3H4, has a significant effect on the efficiency of the laser despite the relatively short lifetime of the 3F4 energy level. Energy migration of the excitation at the 3F4 level through the process 3F4, 3H6 --> 3H6, 3F4 may be enhancing the cross-relaxation mechanism. We also show the importance of reducing the level of clustering of the Tm3+ ion when it is doped into silica by use of appropriate amounts of Al3+ codopant. For Tm3+ concentrations of >1 wt. %, Al3+/Tm3+ concentration ratios of > 10 are recommended forreducing scattering losses, quenching the lifetime, or both.