Optical Test Apparatus Using Differential Light Penetration Depths
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Current non-contact testing methods for defects in materials, such as semiconductors and metals, face challenges in accurately measuring thickness and detecting internal defects without causing impairment, particularly due to limitations in light penetration depth and signal-to-noise ratio.
Innovation Solution
An optical test apparatus is designed with a pump beam generating unit producing a short-pulse laser with a short light penetration depth to generate an elastic wave, and a probe beam with a longer light penetration depth to measure thickness and detect defects, improving signal-to-noise ratio and reducing specimen impairment.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If a single light beam is used for both generating elastic waves and measuring thickness/defects, then the device complexity is reduced, but the measurement precision deteriorates due to insufficient signal-to-noise ratio and specimen impairment
Solution Approach 1:
The invention divides the light beam into two separate beams: a pump beam for generating elastic waves and a probe beam for measuring thickness and defects. This segmentation allows each beam to be optimized for its specific function, with the probe beam having longer penetration depth and higher signal-to-noise ratio, thereby resolving the contradiction between device simplicity and measurement precision
Solution Approach 2:
The pump beam serves multiple functions: generating elastic waves for defect detection, creating surface acoustic waves, and providing a timing reference for the measurement process. This multi-functionality maintains device simplicity while enabling precise measurements through the separate probe beam
2Reliability
If light penetration depth is increased to measure internal defects, then the detection capability is improved, but the signal-to-noise ratio deteriorates
Solution Approach 1:
The invention applies different optical properties to different parts of the system: the pump beam uses shorter penetration depth for localized elastic wave generation at the surface, while the probe beam uses longer penetration depth for deep internal defect detection. This local quality differentiation allows simultaneous optimization of both surface excitation and deep tissue measurement
Solution Approach 2:
The pump beam operates in pulsed mode to generate periodic elastic waves, creating a time-gated measurement window. This periodic action allows the probe beam to measure during specific time intervals when the elastic wave is present, improving signal-to-noise ratio by synchronizing the measurement with the wave generation cycle
3Measurement precision
If elastic wave amplitude is increased to improve defect detection, then the detection sensitivity is improved, but the specimen impairment worsens
Solution Approach 1:
The invention replaces direct mechanical excitation methods with optical excitation using pump and probe beams. This substitution eliminates mechanical contact and associated damage while maintaining high detection sensitivity through non-contact elastic wave generation and measurement
Solution Approach 2:
The invention changes the physical parameters of the light beams: the pump beam uses high peak power in short pulses to generate strong elastic waves without excessive heat accumulation, while the probe beam uses lower power with longer penetration depth for sensitive detection. This parameter optimization allows high detection sensitivity with minimal specimen damage
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
The apparatus enables non-contact, high-accuracy internal probing of materials, measuring thickness and detecting defects while minimizing harm to the specimen by optimizing light penetration depths and improving signal quality.
Implementation Method 1
a pump beam generating unit for applying a pump beam toward a specimen; a probe beam generating unit for applying a probe beam toward the specimen, wherein a light penetration depth of the probe beam relative to the specimen is longer than a light penetration depth of the pump beam relative to the specimen
Implementation Method 2
A processing circuit acquires information on the specimen based on a time-series change in intensity of the reflected beam
Implementation Method 3
the elastic wave changes a complex refractive index inside the specimen, as well as causes an intensity change in the reflected beam
Implementation Method 4
A photodetector receives the reflected beam
Data Source
Figure 1~2
Figure 3~4
Figure 5~6
AI summary
According to one arrangement, an optical test apparatus (10) includes a pump beam generating unit (11), a probe beam generating unit (12), and a photodetector (13). The pump beam generating unit (11) generates a pump beam for exciting an elastic wave in a specimen. The probe beam generating unit (12) generates a probe beam. The photodetector (13) receives the probe beam. A first light penetration depth of the probe beam relative to the specimen is longer than a second light penetration depth of the pump beam relative to the specimen.