Do CGHs require regular calibration?

Similar to other precision optical elements, CGHs can be used indefinitely without calibration, given they are not damaged, altered, or exposed to harsh environments. They are fabricated on fused silica substrates which are stable over time. The grating pattern is either etched into the glass or is a chrome-on-glass grating. The back surface of the CGH has an anti-reflection coating at the test wavelength. All of these primary elements of the CGH are robust over time and do not require recalibration for general-purpose testing.

For high-precision testing, where single-digit nanometer uncertainty from the CGH is required, in-situ calibration is recommended to correct small changes over time in temperature which can slightly affect the transmitted wavefront of the CGH.