Abstract
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.
Highlights
Μ s- or ns-wide pulses display enormous potential in some areas such as plastic and polymer processing, laser scalpels, non-invasive medical diagnosis, infrared countermeasures, and pumping optical parametric oscillator (OPO) and others
In this paper, using a designed semiconductor saturable absorber mirror (SESAM) optimized for ~3 μ m, we report the first investigation of a dual wavelength, passively switched, cascade pulsed Ho3+-doped fluoride fiber laser
The oscillator experienced different regimes: continuous wave (CW), stable ~3 μ m Q-switching, stable ~3 μ m Q-switching and stable ~2 μ m gain switching with a half repetition rate as ~3 μ m, stable ~3 μ m Q-switching and unstable ~2 μ m gain switching with jumping repetition rate, and stable ~3 μ m Q-switching and stable ~2 μ m gain switching with the same repetition rate as ~3 μ m
Summary
Μ s- or ns-wide pulses display enormous potential in some areas such as plastic and polymer processing, laser scalpels, non-invasive medical diagnosis, infrared countermeasures, and pumping OPOs and others. SESAM, as a mature SA, is constantly improving through innovations It has a remarkably excellent performance as well as the ability of customize some of its parameters, i.e., modulation depth, non-saturable loss, recovery time, etc., mainly attributing to well-developed semiconductor technologies such as bandgap and defect engineering and growth. SESAM has been widely applied into ~2 μ m Q-switching[22,33,34] and recently into ~3 μ m Q-switching where a structured SESAM whose InAs absorber layer was sandwiched between an Au-coated mirror and a GaAs wafer[23] This new structure was designed to reduce the fabrication time and material consumption while improving the damage threshold and feedback band providing the feasibility of broadband Q-switching. The employment of external driving AOM undoubtedly removes the intrinsic compactness and simplicity of fiber lasers
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