Ho:YAG, Tm:YAG and Er:YAG are the three workhorse gain media for mid-infrared surgical and eye-safe lasers. They all share the YAG host but emit at very different wavelengths with very different tissue interactions: Ho:YAG and Tm:YAG around 2 µm (the eye-safe band used in soft-tissue surgery and lithotripsy), and Er:YAG at 2.94 µm (peaked at the water absorption band, for precise hard- and soft-tissue ablation). This guide compares them so you can choose the right crystal for a medical, surgical or eye-safe laser system.
| Property | Ho:YAG | Tm:YAG | Er:YAG |
|---|---|---|---|
| Formula | Ho:Y3Al5O12 | Tm:Y3Al5O12 | Er:Y3Al5O12 |
| Emission wavelength | ~2.1 µm (2090 nm) | ~2.0 µm (2015 nm) | 2.94 µm |
| Eye-safety | Eye-safe (cornea absorbs) | Eye-safe | Mid-IR (strong surface absorption) |
| Pump scheme | Pumped by a Tm laser (780–790 nm less direct) | Direct diode ~785 nm; cross-relaxation → high efficiency | Flashlamp or ~970 nm diode |
| Water absorption | Moderate (penetrates tissue ~0.3–0.4 mm) | Moderate | Very strong (penetrates only a few µm) |
| Typical clinical use | Lithotripsy, BPH, orthopedics, urology | Soft-tissue surgery, ablation, Ho-pump source | Dental, dermatology / skin resurfacing, bone |
| Pulse character | Free-running / Q-switched, high pulse energy | CW and pulsed | Pulsed (free-running), precise ablation |
Holmium-doped YAG emits at ~2.1 µm, an eye-safe wavelength absorbed moderately by water, giving a controlled penetration depth (~0.3–0.4 mm) ideal for cutting and ablation in a fluid medium. This makes Ho:YAG the standard laser for urology (kidney-stone lithotripsy, BPH/enucleation), orthopedics and some ENT and gynecology procedures. Modern Ho:YAG systems are typically pumped by a Tm laser (the "Tm-fiber-pumped Ho:YAG" architecture) for high efficiency and high average power. View Ho:YAG crystals.
Thulium-doped YAG emits near 2.0 µm and can be pumped directly by ~785 nm InGaAs laser diodes. A key advantage is cross-relaxation: each absorbed pump photon excites two Tm ions, giving high slope efficiency. Tm lasers are used directly for soft-tissue surgery and, increasingly, as efficient pump sources for Ho:YAG (see the 2.1 µm Ho:YAG pumped by Tm laser application note). View Tm:YAG crystals.
Erbium-doped YAG emits at 2.94 µm, right at a strong water (OH) absorption peak, so its energy is absorbed in a very thin surface layer (a few micrometres). That gives extremely precise tissue ablation with minimal thermal damage — ideal for dental hard-tissue work (caries, etching), dermatology (skin resurfacing, wrinkle reduction), and bone procedures. Er:YAG is typically flashlamp-pumped or diode-pumped around 970 nm and operated in short pulses. View Er:YAG crystals.
For high-power Ho or Tm rods, consider diffusion-bonded end-capped designs (e.g. YAG / Ho:YAG / YAG) to manage thermal load. For a custom-cut, coated medical-grade crystal, contact sales@aogcrystal.com with your target wavelength, pulse energy and duty cycle.
Which crystal for kidney-stone lithotripsy? Ho:YAG at 2.1 µm — its water absorption and pulse energy fragment stones effectively through a fiber in a fluid-filled ureter.
Why is Er:YAG good for teeth and skin? Its 2.94 µm line coincides with the water absorption peak, so each pulse removes only a thin layer of tissue with little heat spread.
Is Tm:YAG eye-safe? Yes — like Ho:YAG, its ~2 µm output is absorbed by the cornea before reaching the retina, making the 2 µm band "eye-safe."
For more information on crystal materials, please consult info@aogcrystal.com