  Energy resolution is an important figure of merit for TES microcalorimeter.
We propose a laser system to measure the energy resolution of TES
microcalorimeter with a 1550 nm laser source. Compared to method that
characterizes the performance by irradiating the detector using X-ray photons
from a radioactive source placed inside the refrigerator, our system is safer
and more convenient. The feasibility of this system has been demonstrated in
the measurement of an Al/Ti bilayer TES microcalorimeter. In this experiment,
the tested detector showed a energy resolution of 72 eV in the energy range
from 0.2 keV to 0.9 keV
