1.6-W self-referenced frequency comb at 2.06 μm using a Ho:YLF multipass amplifier

Area of Science:

• Laser Physics
• Quantum Optics
• Nonlinear Optics

Background:

• Optical frequency combs are crucial for precision measurements.
• Generating high-power combs in the mid-infrared (mid-IR) is challenging.
• Erbium (Er)-doped fiber lasers offer broad supercontinuum generation but limited mid-IR power.

Purpose of the Study:

• To generate a high-power optical frequency comb at 2.06 μm.
• To utilize a Ho:YLF multipass amplifier for comb generation.
• To achieve precise control over the comb's spectral properties.

Main Methods:

• Seeding a Ho:YLF multipass amplifier with the long-wavelength supercontinuum tail of an octave-spanning Er:fiber comb source.
• Characterizing the amplifier's gain spectrum and output comb properties.
• Employing a self-referencing f-2f interferometer and phase-locking loop for spectral narrowing.

Main Results:

• Generation of a 20 nm bandwidth optical frequency comb centered at 2.06 μm.
• Achieved net gain >30 dB in the Ho:YLF amplifier (2048–2068 nm).
• Output comb exhibited 100 MHz mode spacing, 20–370 μW power per mode, 1.6 W total power, and 508 fs transform-limited pulse duration.
• Spectral narrowing of the offset frequency to <17 Hz was demonstrated.

Conclusions:

• The Ho:YLF multipass amplifier successfully generated a high-power, narrow-linewidth optical frequency comb in the 2 μm spectral region.
• This work demonstrates a viable method for extending optical frequency comb technology to longer wavelengths.
• The achieved performance opens possibilities for applications requiring high-power mid-IR frequency combs.