Cascade transitions of rare earth ions involved in infrared host fiber provide the potential to generate dual or multiple wavelength lasing at mid-infrared region. In addition, the fast development of saturable absorber (SA) towards the long wavelengths motivates the realization of passively switched mid-infrared pulsed lasers. In this work, by combing the above two techniques, a new phenomenon of passively Q-switched ~3 μm and gain-switched ~2 μm pulses in a shared cavity was demonstrated with a Ho3+-doped fluoride fiber and a specifically designed semiconductor saturable absorber (SESAM) as the SA. The repetition rate of ~2 μm pulses can be tuned between half and same as that of ~3 μm pulses by changing the pump power. The proposed method here will add new capabilities and more flexibility for generating mid-infrared multiple wavelength pulses simultaneously that has important potential applications for laser surgery, material processing, laser radar, and free-space communications, and other areas.
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Funding: National Nature Science Foundation of China (Grant No. 61435003,
61377042 and 61327004), European Commission’s Marie Curie International Incoming Fellowship (Grant No. 911333), Open Fund of State Key Laboratory of Modern Optical Instruments of Zhejiang University, Open Fund of Medical Optical Key Laboratory of Jiangsu Province (Grant No. JKLMO201403), Fundamental Research Funds for the Central Universities (Grant No. ZYGX2013J058) Open Fund of High Energy Laser Science and Technology Key Laboratory of China Academy of Engineering Physics (Grant No. 2013005580)