Two‐photon absorption peculiarities of potassium dihydrogen phosphate crystal at 216 nm

The two‐photon absorption coefficient of potassium dihydrogen phosphate at λ=216 nm was measured to be β=(6.0±0.5)10−10 cm/W. The presence of impurities is shown to increase nonlinear losses at very low intensities, I≊107 W/cm2.