US 11,815,447 B2
Femtosecond laser-based ultrasonic measuring apparatus for 3D printing process and 3D printing system having the same
Hoon Sohn, Daejeon (KR); and Peipei Liu, Daejeon (KR)
Assigned to Korea Advanced Institute of Science and Technology, Daejeon (KR)
Filed by Korea Advanced Institute of Science and Technology, Daejeon (KR)
Filed on Dec. 8, 2020, as Appl. No. 17/114,647.
Claims priority of application No. 10-2019-0179190 (KR), filed on Dec. 31, 2019.
Prior Publication US 2021/0199567 A1, Jul. 1, 2021
Int. Cl. G01N 21/17 (2006.01); B33Y 30/00 (2015.01); G01N 21/88 (2006.01); B33Y 50/02 (2015.01); B22F 12/90 (2021.01); B22F 10/25 (2021.01)
CPC G01N 21/1702 (2013.01) [B22F 12/90 (2021.01); B33Y 30/00 (2014.12); B33Y 50/02 (2014.12); G01N 21/8806 (2013.01); B22F 10/25 (2021.01); G01N 2201/067 (2013.01); G01N 2201/06113 (2013.01)] 13 Claims
OG exemplary drawing
 
1. A three dimensional (3D) printing system with a function of femtosecond laser-based ultrasonic measurement, comprising:
a base material source for supplying a base material for 3D printing;
a nozzle arranged to feed the base material from the base material source to a printing object;
a 3D printing laser source for irradiating a printing laser beam to molt the base material, thereby forming a molten pool on the printing object;
a femtosecond laser source disposed coaxially with the 3D printing laser source, and configured to irradiate a femtosecond laser beam to inspect a state of the printing object formed by melting the base material using the 3D printing laser beam;
a first beam splitter configured to separate the femtosecond laser beam from the femtosecond laser source into a first femtosecond laser beam and a second femtosecond laser beam;
an electric/acoustic optical modulator configured to modulate the first femtosecond laser beam, at a predetermined modulation frequency in a pulse picking method, into a pump laser beam;
a time delay unit configured to delay the second femtosecond laser beam in time to be a probe laser beam with a time delay by guiding the second femtosecond laser beam to pass through an adjusted length of optical path;
a photo detector configured to detect the probe laser beam reflected from the printing object and convert the detected probe laser beam into an electrical signal; 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 the modulation frequency, and a low pass filter for passing a low frequency band of the demodulated signal,
a reflection mirror unit including a plurality of reflection mirrors for changing optical paths of the printing laser beam, the pump laser beam, and the probe laser beam to be arranged coaxially;
a second beam splitter, disposed on a coaxial path of the printing laser beam, the pump laser beam, and the probe laser beam, allowing the printing laser beam, the pump laser beam, and the probe laser beam to pass toward the printing object through the nozzle, and reflecting the probe laser beam incident on and then reflected from the printing object toward the photo detector; and
a focus lens for focusing the printing laser beam from the reflection mirror unit onto the printing object,
wherein the detected amplitude and phase are used for estimating physical properties of the printing object and detecting defects of the printing object,
wherein the pump laser beam is to generate ultrasonic waves by causing the printing object to be excited, and the probe laser beam is to measure ultrasonic waves to inspect a state of the printing object, and
wherein the probe laser beam reflected by the printing object has a shorter pulse interval than the pump laser beam.