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Gamma-ray spectroscopy using low-temperature microcalorimeter arrays has demonstrated breakthrough energy resolution, establishing an important new technique for the precise characterization of radioactive samples. However, the extraordinary dynamic range of these pixels, spanning tens of electronvolts to hundreds of kiloelectronvolts, places stringent requirements on the calibration accuracy of each pixel. In this report, we describe the design, development, and initial reflectivity-map testing of a new optical pulser intended for the precise determination of energy calibrations of microcalorimeter pixels and pixel arrays. A high-resolution XYZ scanner combined with 3 K optics achieving a 3-μm focused spot permit in situ imaging and precise placement of the energy deposition on the detector. Absolute absorbed power can be calibrated via a precision measurement of detector thermal stand-off.