Influence of the piezoelectric ringing on the polarisation contrast of the KRTP Pockels cell in the modulation frequency range up to 10 MHz

Pockels cell is one of the major components limiting the pulse repetition rate of high-power laser sources. The birefringence of the electro-optical crystal is controlled by the electric voltage which allows high-frequency modulation of intracavity losses, thus unlocking the MHz frequency band for pulse repetition rate. The purpose of this work was to investigate the influence of the piezoelectric ringing on the polarisation contrast of the potassium rubidium titanyl phosphate (KRTP) based electro-optical modulator in the frequency range up to 10 MHz. This was done by complex impedance and polarisation contrast measurements, as well as comparison to numerically identified fundamental frequencies of the crystal. The behaviour and dominant mechanism behind the effects of piezoelectric ringing were found to be distinct in three modulation frequency ranges: up to 2 MHz, above 2 MHz, and above 6.3 MHz. In particular, above 6.3 MHz, no piezoelectric-ringing-induced depolarisation was observed. These findings make KRTP based Pockels cells attractive for high-repetition-rate pulse picking applications.