Cr,Tm,Ho:YAG (CTH:YAG) Single Crystal

Advantages

• Broad flashlamp pump absorption: Cr³⁺ acts as a broad-band sensitizer, absorbing flashlamp radiation in the visible region (400-800 nm) and transferring energy to Tm³⁺, which then transfers to Ho³⁺. This triple-doping scheme enables efficient flashlamp-pumped 2 μm laser operation.
• Eye-safe 2.1 μm emission with high water absorption: The ⁵I₇ → ⁵I₈ transition of Ho³⁺ produces output at approximately 2.094 μm, which is strongly absorbed by water and biological tissue, and is safe for the eye.
• CTH:YAG operates at room temperature, eliminating the need for cryogenic cooling required by some other 2 μm laser systems.
• Ideal pump source for mid-IR OPOs: The 2.1 μm output serves as an excellent pump source for 3–5 μm mid-infrared optical parametric oscillators.
• High slope efficiency under laser pumping: Power slope efficiencies exceeding 40% have been achieved when pumping Cr:Tm:Ho:YAG at 647.1 nm.

Typical Specifications

• Chemical formula: Cr,Tm,Ho:Y₃Al₅O₁₂
• Crystal structure: Cubic garnet, space group Ia3d
• Lattice constant: 12.01 Å
• Doping concentrations: Ho: 0.3–0.4 at%; Cr: 0.3–1.2 at%; Tm: 5–6 at%
• Laser transition: ⁵I₇ → ⁵I₈
• Laser wavelength: 2.094 μm
• Photon energy: 9.55 × 10⁻²⁰ J
• Emission cross-section: 7 × 10⁻²¹ cm²
• Fluorescence lifetime: 8.5 ms
• Refractive index: 1.80 @ 2.08 μm
• Diode pump band: 781 nm
• Main pump band: 400–800 nm
• Absorption linewidth: 4 nm
• Melting point: 1970 °C
• Density: 4.56 g/cm³
• Mohs hardness: 8.5
• Thermal conductivity: 14 W/(m·K) @ 20°C; 10.5 W/(m·K) @ 100°C
• Thermal expansion coefficient: 7.8 × 10⁻⁶/K
• Dielectric constant: 11.7

Standard Fabrication Specifications

• Orientation: <111> or <100> within 5°
• Rod sizes: Diameter 3–6 mm; Length 50–120 mm
• Dimension tolerance: Diameter +0/−0.1 mm; Length ±0.5 mm
• Parallelism: ≤30 arc sec
• Perpendicularity: ≤5 arc min
• Surface flatness: λ/10 @ 633 nm
• Wavefront distortion: <λ/4 @ 632 nm
• Surface quality: 10/5 Scratch/Dig per MIL-O-1380A
• Clear aperture: >90%
• Chamfer: 0.2 mm at 45° ± 5°
• AR coating: R ≤ 0.25% @ 2094 nm

Main Applications

• Medical laser surgery: CTH:YAG lasers are used for tissue ablation, coagulation, and cutting in urology, orthopedics (synovectomy), and general surgery, benefiting from the strong water absorption of 2.1 μm radiation .
• LIDAR and remote sensing: The eye-safe 2.1 μm output is suitable for coherent Doppler wind LIDAR and atmospheric monitoring .
• Mid-infrared OPO pumping: The 2.1 μm output serves as an ideal pump source for ZGP-based optical parametric oscillators to generate 3–5 μm radiation .
• Military and countermeasures: Deployed in laser rangefinders, target designation, and photoelectric countermeasure systems .
• Flashlamp-pumped high-energy lasers: Output energies exceeding 3 J and up to 17 J have been demonstrated in single-shot operation .
• Single-longitudinal-mode microchip lasers: LD-pumped CTH:YAG microchip lasers have achieved 31 mW single-longitudinal-mode output at 2.09 μm with a tuning coefficient of 1.4 GHz/°C .