Highly Sensitive Pulsed Digital Holography for Built-in Defect Analysis with a Laser Excitation

Area of Science:

• Optics and Photonics
• Materials Science
• Non-Destructive Testing

Background:

• Non-destructive testing (NDT) is crucial for evaluating material integrity without causing damage.
• Digital holographic interferometry (DHI) offers high-resolution surface deformation measurement.
• Traditional DHI methods often require external excitation sources, which can be cumbersome or impractical.

Purpose of the Study:

• To develop a highly sensitive, noninvasive method for defect analysis in thin structures.
• To integrate a synchronous optical excitation source within an all-optical arrangement for DHI.
• To demonstrate the effectiveness of the proposed method for identifying and evaluating defects in thin metal sheets.

Main Methods:

• Utilized a Q-switched double-pulsed ruby laser with frequency doubling (347 nm) for high-sensitivity defect analysis.
• Implemented an all-optical setup employing a second laser pulse (694 nm) from the same ruby laser as a synchronous excitation source for DHI.
• Captured two holograms using a CCD camera, corresponding to two UV laser pulses with a short time separation (10-50 µs).
• Performed phase subtraction between the two digital holograms to generate a fringe phase map indicating specimen deformation.

Main Results:

• Achieved highly sensitive, noninvasive defect detection in thin structures.
• Demonstrated successful identification and evaluation of defects in thin metal sheets.
• The method showed increased sensitivity due to the use of a shorter wavelength (347 nm).
• The integrated synchronous optical excitation eliminated the need for external physical excitation devices.

Conclusions:

• The proposed all-optical method provides a highly sensitive and noninvasive approach for defect analysis in thin structures.
• The use of a shorter wavelength and synchronous optical excitation enhances measurement sensitivity and simplifies the experimental setup.
• This technique is effective for the identification and evaluation of defects in thin metal sheets, offering advantages over conventional methods.