InAs/GaSb superlattice SESAM mode-locked fluoride fiber laser at 2.8 µm.

Area of Science:

• Optics and Photonics
• Materials Science
• Laser Physics

Background:

• Mid-infrared (MIR) lasers are crucial for spectroscopy and sensing.
• Fluoride fiber lasers offer advantages for MIR generation.
• Developing reliable mode-locking mechanisms for MIR fiber lasers remains a challenge.

Purpose of the Study:

• To demonstrate a mode-locked fluoride fiber laser operating at 2.8 µm.
• To utilize an Indium Arsenide/Gallium Antimonide (InAs/GaSb) superlattice (SL) semiconductor saturable absorber mirror (SESAM) for mode-locking.
• To characterize the nonlinear optical properties and reliability of the InAs/GaSb SL SESAM.

Main Methods:

• Fabrication and characterization of an InAs/GaSb SL SESAM.
• Z-scan measurements to determine nonlinear optical properties (saturation fluence, modulation depth, damage threshold).
• Integration of the SESAM into an Erbium-doped ZBLAN fiber laser cavity for mode-locking.

Main Results:

• The InAs/GaSb SL SESAM exhibited off-bandgap nonlinearity at 2.8 µm with a saturation fluence of 15.9 µJ/cm², modulation depth of 2.4%, and damage threshold of 10.4 mJ/cm².
• A maximum average output power of 1.16 W was achieved from the 2.8 µm mode-locked laser with a pulse duration of 28.1 ps.
• Continuous mode-locking was sustained for 36 hours at 224 mW average power, confirming SESAM reliability.

Conclusions:

• The InAs/GaSb SL SESAM is a viable and reliable saturable absorber for 2.8 µm mode-locked fluoride fiber lasers.
• This work paves the way for developing robust MIR fiber laser sources.
• The demonstrated laser system shows potential for applications requiring stable MIR ultrashort pulses.