| Abstract [eng] |
Investigation of the Resonance Behaviour of Pockels Cells Electro-optical modulators are essential for most high repetition and high-power laser systems. There is a general need for a Pockels cell that achieves the maximum frequency of modulation and good polarization contrast. In this study, the operation of such elements is reviewed and the main effects of the electro-optic modulator are discussed. Processes for acoustic wave formation and absorption are also briefly described. The aim of this work was to investigate resonant acoustic phenomena occurring in electro-optical crystal and to measure their influence on the polarization contrast of the Pockels cell in the modulation frequency range up to 10 MHz. Electro-optical KRTP crystal is used in this study due to its low half-wave voltage, which allows to achieve extremely high modulation frequencies explored in this study. In order to better understand the formation of resonant acoustic waves, a finite element analysis was used to calculate the mechanical resonance modes of the Pockels cell. Electrically and optically measured fundamental resonance frequencies coincide with resonance modes calculated by computer simulation. It was found that at modulation frequencies below 2 MHz, the change in the Pockels cell's polarization contrast is induced by the photoelastic effect, which is caused by resonant acoustic wave. However, at this frequency range the decrease in polarization contrast is relatively small. At higher modulation frequencies crystal temperature dependence on the frequency was observed. It was found that when the modulation frequencies coincide with high order harmonics of the fundamental resonant frequency, the deterioration of polarization contrast is caused by the formation of a temperature gradient in the crystal. This work demonstrated the potential of the KRTP electro-optical modulator and revealed the resonant phenomena occurring in a wide modulation frequency range. The findings of this study provide the basis for further research in order to reduce the influence of resonant acoustic phenomena on the polarization contrast of electro-optical modulators. |
