State-switchable and wavelength-tunable gain-switched mid-infrared fiber laser in the wavelength region around 2.94 µm.

We demonstrate a gain-switched singly Ho3+-doped ZBLAN fiber laser for the first time in the wavelength region around 2.94 µm which circumvents the strong water vapor lines. Four switchable gain-switched temporal states with 1/n (n = 4,3,2,1) pump repetition rates are first observed. The influences of pump power (pulse energy), repetition rate, duty cycle (pulse duration), and laser wavelength on their characteristics are studied, respectively. The results indicate that high pump repetition rate, large pump duty cycle, and short laser wavelength are beneficial for obtaining more gain-switched temporal states. For the case (n = 1), the increased pump repetition rate contributes to the increased pulse duration while decreased pulse energy and peak power. While µs-level pump pulse duration variation has an almost negligible effect on them. By introducing a plane ruled grating, the wavelength tuning was performed yielding a tuning range of 105 nm from 2895.5 nm to 3000.5 nm which just overlays the peak region of liquid water absorption. Finally, further optimizing of laser performances is discussed as well. This demonstration is helpful for preliminarily designing, prior to constructing a mid-infrared gain-switched laser which can find direct applications in laser surgery.

Cascaded gain-switching in the mid-infrared region.

In this report, we demonstrate mid-infrared dual-waveband (i.e., ~3 µm and ~2 µm) pulses from a cascaded gain-switched Ho3+-doped ZBLAN fiber laser by the use of hybrid pumping of 1150 nm CW and pulse LDs for the first time. Stable ~3 µm gain-switched pulses with the maximum output power 262.14 mW and shortest pulse duration of 0.824 µs were first gained at the repetition rate of 80 kHz and wavelength of 2928.5 nm. Then stable ~2 µm gain-switched pulses at 2068 nm were achieved at a switchable repetition rate between 40 kHz and 80 kHz. The maximum output power and shortest pulse duration were 75.23 mW and 0.787 µs, respectively (not simultaneously). Between them, there is a power-dependent µs-order time delay. This dual-waveband laser source has great potential in laser surgery, material processing.