ZnTe (Zinc Telluride) crystals are used for THz generation by optical rectification process. Optical rectification is a difference frequency generation in media with large second order susceptibility leading to a bandwidth from 0 to several THz. GaSe (Gallium Selenide) crystals used for THz generation show a large bandwidth of up to 41 THz. GaSe crystal features high damage threshold and large nonlinear optical coefficient.