Wavelength Conversion Device Resonator Reflectance Noise Control
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Solution Overview
Problem
Wavelength conversion devices with short wavelength lasers suffer from intensity noise, which degrades image quality in applications like wafer inspection, where high-speed scanning is required, leading to potential black spots and impaired inspection accuracy.
Innovation Solution
A wavelength conversion device and method where the reflectance of the input coupling element is selected based on specific equations to reduce frequency jitter and noise in the wavelength converted light, ensuring the frequency line width of the external resonator is greater than the frequency jitter of the fundamental wave light source, thereby minimizing noise.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Loss of energy
If impedance matching is performed to maximize wavelength conversion efficiency, then conversion efficiency is improved, but intensity noise increases
Solution Approach 1:
The invention changes the parameter selection criteria from impedance matching (maximizing energy conversion) to frequency line width control (minimizing noise). Specifically, the reflectance of the input coupling element is selected based on equations (1) and (2) that ensure the frequency line width of the external resonator is greater than the frequency jitter of the fundamental wave light source, rather than based on maximizing conversion efficiency through impedance matching.
2Productivity
If a short wavelength laser is used for high-speed scanning, then productivity is improved, but intensity noise causes measurement precision deterioration
Solution Approach 1:
The invention changes the operating parameters of the wavelength conversion device to prioritize noise reduction over maximum output power. By selecting the reflectance based on frequency line width requirements rather than power maximization, the system maintains sufficient output for high-speed scanning while minimizing intensity noise that would otherwise degrade inspection accuracy during rapid wafer scanning.
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
This approach effectively reduces noise in wavelength converted light, allowing for improved image quality and inspection accuracy in high-speed scanning applications, and can utilize relatively inexpensive and small fundamental wave light sources like DFB fiber lasers.
Implementation Method 1
an external resonator 120 including an input coupling element 121 having a mirror with a predetermined transmittance, mirrors 122 to 124, and a nonlinear optical crystal 125 placed between the input coupling element 121 and the mirror 122
Data Source
AI summary
A wavelength conversion device is disclosed. The wavelength conversion device includes at least a fundamental wave light source and an external resonator, where a reflectance Rin of an input coupling element that inputs light from the fundamental wave light source to the external resonator is selected as represented by the equations 1 and 2, when a frequency jitter of the fundamental wave light source is Δfjitter, a resonator length of the external resonator is Lcav, a frequency line width of the external resonator is Δνcav, a total internal loss of the external resonator is δ, and a speed of light is c.Δvcav=cLcav×1-Rin(1-δ)π(Rin(1-δ))1/4(1)Δvcav≧Δfjitter(2)