Lithium triborate (LiB3O5) or LBO is a non-linear optical crystal.

It has a wide transparency range, moderately high nonlinear coupling, high damage threshold and desirable chemical and mechanical properties.

This crystal is often used for second harmonic generation (SHG, also known as frequency doubling), for example of Nd:YAG lasers (1064 nm → 532 nm).

In the latter case the crystal has to be heated or cooled depending on the wavelength.

Lithium triborate was discovered and developed by Chen Chuangtian and others of the Fujian Institute of Research on the Structure of Matter, Chinese Academy of Sciences.