Substrate inspection apparatus and method of inspecting a substrate using the same

A substrate inspection apparatus comprising:

• a laser light source configured to emit a femtosecond laser beam;
• an optical splitter configured to split the femtosecond laser beam into a first laser beam and a second laser beam;
• a delay stage configured to receive the second laser beam from the optical splitter and configured to change a relative time delay of the second laser beam with respect to the first laser beam;
• a modulator optically connected to the optical splitter and configured to change the second laser beam;
• and
• a feedback system configured to sense the second laser beam reflected from a substrate and electrically connected to the modulator.