Holmium-doped fiber amplifier for pumping a ZnGeP₂ optical parametric oscillator

Area of Science:

• Laser Physics
• Nonlinear Optics
• Materials Science

Background:

• Developing high-power fiber lasers at longer wavelengths is crucial for various applications, including optical frequency conversion.
• Holmium-doped gain media offer potential for generating laser light in the 2-micron spectral region.

Purpose of the Study:

• To develop and characterize a holmium-doped all-fiber master oscillator power amplifier (MOPA) system operating at 2108 nm.
• To investigate the performance limitations and efficiency of the MOPA system.
• To demonstrate the utility of the MOPA for optical frequency conversion applications.

Main Methods:

• Construction of a three-stage holmium-doped all-fiber MOPA.
• Characterization of pulse energy, duration, beam quality, and polarization.
• Investigation of gain and efficiency limitations, including measurements of non-saturable absorption.
• Demonstration of mid-IR optical parametric oscillation (OPO) using the MOPA as a pump source.

Main Results:

• The MOPA system delivered pulses with 0.52 mJ energy at a 10 kHz repetition rate.
• Output pulses exhibited a near-square temporal profile of 50 ns duration, diffraction-limited beam quality, and linear polarization.
• Quenching effects, inferred from non-saturable absorption measurements, were identified as a limiting factor for gain and efficiency in the final amplification stage.
• A mid-IR conversion efficiency of 59% was achieved by directly pumping a ZnGeP2 optical parametric oscillator.

Conclusions:

• The developed holmium-doped all-fiber MOPA system is a viable source for high-energy 2108 nm laser pulses.
• Quenching effects in holmium fibers present challenges for maximizing amplifier efficiency.
• The MOPA system effectively serves as a pump source for efficient mid-IR optical frequency conversion.