A system of controlling a wavelength of a laser beam is provided. The
system comprises a stage for supporting a wafer, an optical convergence
unit for emitting the laser beam moving in an optical path toward the
stage, and a specific wavelength detecting sensor. The specific
wavelength detecting sensor is disposed between the optical convergence
unit and the stage. It includes a laser beam absorbing structural body
for absorbing a specific wavelength of the laser beam emitting toward the
stage. A wavelength controlling unit for selectively controlling the
wavelength of the laser beam is also provided.