Thermal Lens Calculator
Estimate thermal lens focal length and dioptric power in pumped laser rods.
In diode-pumped solid-state lasers, a fraction of absorbed pump power — typically 25–40% for Nd:YAG depending on quantum defect and non-radiative losses — is converted to heat rather than signal photons. The resulting radial temperature gradient in the laser rod induces a refractive index gradient via the thermo-optic coefficient dn/dT, creating a positive lens with focal length f_th = K·A/(P_heat·(dn/dT)·L), where K is thermal conductivity, A is the rod cross-section, and L is the rod length. A stronger thermal lens reduces intracavity beam waist, degrades beam quality, and shifts the cavity stability operating point. This calculator accepts rod diameter, length, absorbed pump power, heat fraction, and material parameters (with presets for Nd:YAG, Nd:YVO₄, Yb:YAG, and Ti:sapphire) to return thermal focal length in mm and dioptric power in m⁻¹.