Highly efficient continuous-wave Tm³⁺:YLF cascade laser operating at telecommunication wavelengths

Area of Science:

• Materials Science
• Laser Physics
• Spectroscopy

Background:

• Continuous-wave (CW) laser operation around 1.5 µm is crucial for various applications, including telecommunications and medical treatments.
• Thulium (Tm³⁺)-doped materials are promising candidates for generating laser light in this wavelength range.
• Self-termination due to long-lived lower laser levels can hinder efficient CW laser performance.

Purpose of the Study:

• To investigate Tm³⁺-doped YLF crystals for CW laser operation at 1.5 µm.
• To analyze spectroscopic properties and optimize doping concentrations.
• To circumvent laser self-termination using a cascade laser scheme.

Main Methods:

• Growth of Tm³⁺-doped YLF crystals with varying doping concentrations.
• Spectroscopic investigations including emission, absorption, and gain cross-section measurements.
• Characterization of concentration-dependent lifetime of energy levels.
• Implementation of a cascade laser scheme (³H₄→³F₄→³H₆) to depopulate the lower laser level.
• Ti:sapphire laser pumping at 781 nm.

Main Results:

• Spectroscopic data (emission, absorption, gain cross sections, lifetimes) were obtained.
• The cascade laser scheme effectively depopulated the lower laser level (³F₄).
• Simultaneous CW laser operation was achieved at 1509 nm and 1923 nm.
• Slope efficiencies of 44% (1509 nm) and 35% (1923 nm) were recorded.
• Maximum output powers reached 590 mW (1509 nm) and 670 mW (1923 nm).

Conclusions:

• Tm³⁺-doped YLF crystals are suitable for efficient CW laser operation around 1.5 µm.
• The cascade laser scheme is an effective strategy to overcome self-termination in Tm³⁺ lasers.
• Optimized Tm³⁺-doped YLF crystals offer promising performance for 1.5 µm laser applications.