Ultrafast Dy³⁺:fluoride fiber laser beyond 3 μm

Area of Science:

• Laser Physics and Photonics
• Materials Science
• Spectroscopy

Background:

• Mid-infrared (MIR) lasers are crucial for molecular spectroscopy due to the "molecular fingerprint region."
• Fiber lasers offer advantages in robustness and compactness compared to bulk lasers.
• Directly generating ultrashort pulses beyond 3 μm from fiber lasers remains a significant challenge.

Purpose of the Study:

• To demonstrate a passively mode-locked fiber laser operating beyond 3 μm.
• To achieve ultrashort pulse generation in the 3.1 μm wavelength range.
• To explore the potential for frequency comb generation in the MIR region.

Main Methods:

• Utilized a Dysprosium (Dy3+)-doped fluoride fiber.
• Employed a ring cavity configuration for stable laser operation.
• Implemented nonlinear polarization evolution (NPE) for passive mode-locking.
• Used in-band pumping at 2.8 μm for efficient energy transfer.

Main Results:

• Achieved self-starting, transform-limited mode-locked pulses with durations as short as 828 fs.
• Observed stable laser emission centered around 3.1 μm.
• Attained a maximum average output power of 204 mW, with 4.8 nJ pulse energy and 4.2 kW peak power.
• Demonstrated repetition rates up to 60 MHz.

Conclusions:

• This work presents the first femtosecond mode-locked fiber laser directly emitting beyond 3 μm.
• The developed laser system is a promising platform for generating frequency combs in the molecular fingerprint region.
• This advancement has significant implications for high-resolution molecular spectroscopy and sensing applications.