The parallelism of a Pockels cell refers to the alignment and flatness of the optical surfaces of the cell relative to each other. In other words, it indicates the degree of alignment between the faces of the Pockels cell, assessing their parallelism.

For optimal performance in optical systems, especially those requiring precise polarization control or modulation, it's essential that the optical surfaces of the Pockels cell are parallel. Any deviation from parallelism can lead to distortions or aberrations in the transmitted light beam, affecting the quality of the optical output.

The parallelism of a Pockels cell is typically specified in terms of angular deviation or flatness tolerance. Angular deviation refers to the maximum allowable deviation from perfect parallelism between the optical surfaces, usually expressed in arcseconds or milliradians. Flatness tolerance specifies the maximum allowable variation in the flatness of the optical surfaces across the aperture of the Pockels cell.

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