Femtosecond graphene mode-locked Fe:ZnSe laser at 4.4  µm

Area of Science:

• Laser physics
• Materials science
• Optoelectronics

Background:

• Iron-doped zinc selenide (Fe:ZnSe) lasers are known for their mid-infrared (mid-IR) emission capabilities.
• Achieving ultrafast pulsed operation in Fe:ZnSe lasers has been a significant challenge, limiting their application in advanced scientific fields.

Purpose of the Study:

• To demonstrate the first femtosecond mode-locked operation of an Fe:ZnSe laser.
• To investigate the use of graphene as a saturable absorber for passive mode-locking in this system.
• To characterize the performance of the ultrafast mid-IR laser.

Main Methods:

• Passive mode-locking was achieved using a graphene saturable absorber.
• The laser was pumped using a 7 W Er:ZBLAN fiber laser.
• Output characteristics, including wavelength, repetition frequency, output power, and pulse duration, were measured.

Main Results:

• The Fe:ZnSe laser successfully operated in a femtosecond mode-locked regime at 4.4 µm.
• A repetition frequency of 100 MHz and an average output power of 415 mW were achieved.
• A pulse duration of approximately 732 fs was determined from the autocorrelation function.
• Pulsed nanosecond oscillation and amplitude modulation due to Kerr self-focusing were also observed.

Conclusions:

• This work reports the first femtosecond mode-locked Fe:ZnSe laser, filling a critical gap in laser operating regimes.
• The use of graphene as a saturable absorber proved effective for achieving ultrafast pulsed operation.
• The developed laser represents a significant advancement towards powerful, high-repetition-rate ultrafast mid-IR sources for scientific applications.