Tm:YAG (Thulium-Doped Yttrium Aluminum Garnet) Single Crystal

Advantages

• Eye-safe 2 μm laser emission: Tm:YAG operates on the ³F₄ → ³H₆ transition with a tunable range of 1.87–2.16 μm, falling within the eye-safe spectral region and encompassing strong water vapor and CO₂ absorption bands for remote sensing and medical applications.
• High quantum efficiency via cross-relaxation: At sufficient Tm³⁺ doping concentrations, a beneficial “two-for-one” cross-relaxation process enables quantum efficiencies approaching 2, allowing efficient excitation with commercially available AlGaAs laser diodes at 785 nm.
• Long upper-state lifetime for energy storage: Fluorescence lifetime of approximately 11 ms, enabling efficient Q-switched and pulsed operation.
• High damage threshold: Tm:YAG exhibits a higher damage threshold than Tm:YAP, enabling short-pulse-width, high-peak-power operation (minimum pulse width of 41 ns at 1 kHz, corresponding to 165.7 kW peak power).
• Excellent thermo-mechanical properties: Inherits the robust thermal and mechanical characteristics of the YAG host, including high thermal conductivity (14 W/(m·K) at 20°C), Mohs hardness of 8.5, and good chemical stability.

Typical Specifications

• Chemical formula: Tm³⁺:Y₃Al₅O₁₂
• Crystal structure: Cubic garnet, space group Ia3d
• Lattice constant: a = 12.01 Å
• Tm doping concentration: 0.5-5 at.%
• Laser transition: ³F₄ → ³H₆
• Laser wavelength: 1.87–2.16 μm (primary: ~2.01 μm)
• Diode pump bands: 680 nm, 785 nm
• Absorption cross-section: 7.5 × 10⁻²¹ cm²
• Emission cross-section: 2.9 × 10⁻²⁰ cm² @ 2013 nm
• Fluorescence lifetime: 11 ms
• Refractive index: 1.83 @ 632 nm
• Thermo-optic coefficient: 7.3 × 10⁻⁶/K
• Density: 4.56 ± 0.04 g/cm³
• Melting point: 1970 °C
• Mohs hardness: 8.5
• Thermal conductivity: 14 W/(m·K) @ 20°C; 10.5 W/(m·K) @ 100°C
• Thermal expansion coefficient: <100>: 8.2 × 10⁻⁶/K; <110>: 7.7 × 10⁻⁶/K; <111>: 7.8 × 10⁻⁶/K
• Poisson’s ratio: 0.25

Standard Fabrication Specifications

• Orientation: <111> ± 5°
• Size: Diameter 2–10 mm; length 3–150 mm (customizable)
• Dimension tolerance: Φ: +0/−0.1 mm; L: +0.5/−0 mm
• Parallelism: ≤10 arc sec
• Perpendicularity: ≤5 arc min
• Surface quality: 10/5 Scratch/Dig
• Surface flatness: ≤λ/8 @ 632.8 nm
• Wavefront distortion: ≤λ/8 per 25 mm @ 632.8 nm
• Clear aperture: >95%
• Chamfer: 0.15 ± 0.05 mm
• AR coating: R ≤ 0.25% @ 2 μm

Main Applications

• Medical laser surgery: The 2 μm output is strongly absorbed by water (penetration depth ~0.2 mm), enabling precise tissue ablation with minimal thermal damage. Tm:YAG lasers are used in urology (lithotripsy, prostate vaporization), soft-tissue surgery, and endoscopic procedures.
• LIDAR and remote sensing: Eye-safe 2 μm radiation enables coherent Doppler LIDAR for wind sensing and atmospheric monitoring, with high pulse energies achievable in Q-switched operation.
• Optical parametric oscillator (OPO) pumping: The 2 μm output serves as a pump source for OPOs to generate longer mid-infrared wavelengths (~6.45 μm) for minimally invasive surgery and spectroscopy.
• Material processing: Pulsed Tm:YAG lasers have been applied to marking and welding of transparent thermoplastics (PMMA), demonstrating higher cutting precision than Ho lasers.
• Military and countermeasures: 2 μm eye-safe lasers are used in laser rangefinders, target designation, and photoelectric countermeasures.
• High-power pulsed lasers: Acousto-optic Q-switched Tm:YAG has achieved output powers exceeding 170 W at 10 kHz and pulse energies up to 16.4 mJ at 1 kHz, suitable for high-energy applications.