Femtosecond laser-based ultrasonic measuring apparatus for 3d printing process and 3d printing system having the same

A 3D printing system, comprising:

• a 3D printing laser source configured to form a molten pool on a printing object by irradiating a laser beam to melt a base material supplied to the printing object;
• a base material source configured to supply the base material to the printing object;
• a femtosecond laser source disposed coaxially with the 3D printing laser source, and configured to generate a laser beam irradiated to inspect a state of the printing object;
• a beam splitter configured to separate the laser beam generated by the femtosecond laser source into a pump laser beam and a probe laser beam;
• an electric/acoustic optical modulator configured to modulate the pump laser beam;
• a time delay unit configured to delay the probe laser beam;
• a photo detector configured to detect the probe laser beam reflected by the printing object;
• and
• a lock-in amplifier configured to detect an amplitude and a phase of the output signal from the photo detector, wherein the lock-in amplifier includes a demodulator for demodulating an output signal from the photo detector at a modulation frequency, and a low pass filter for passing a low frequency band of the demodulated signal.