Wavelength-Converted Light Source Stabilization via Polarization Control
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Solution Overview
Problem
Current light source apparatuses for semiconductor inspection face challenges in achieving stable and long-term output stability, particularly in the ultraviolet region, due to issues like speckle, optical noise, and efficiency drops caused by nonlinear optical crystal damage and thermal lens effects, which are not effectively addressed by existing methods.
Innovation Solution
A light source apparatus that includes a laser light source, nonlinear optical crystals, and polarization adjusting means that change the refractive index to stabilize the output of wavelength-converted light, using electro-optical or photoelastic effects to maintain constant polarization and reduce optical noise, along with spatial coherence degrading elements to minimize speckle.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If high-power input light is used to compensate for nonlinear optical crystal degradation, then output stability is maintained, but power consumption increases and optical damage risk increases
Solution Approach 1:
The patent implements automatic power control by separating a portion of the output light, measuring its intensity with a photodetector, and using the measurement to control the pump laser power. This closed-loop feedback system maintains stable ultraviolet output despite crystal degradation over time, eliminating the need for continuous high-power input.
2Object-affected harmful factors
If a rotating diffusion plate is used to reduce speckle, then spatial coherence is degraded, but output intensity fluctuations increase
Solution Approach 1:
The patent uses a photodetector to monitor output light intensity and feeds this information back to a controller that adjusts the pump laser power. This feedback mechanism compensates for the intensity fluctuations caused by the rotating diffusion plate, maintaining stable output while reducing speckle through spatial coherence degradation.
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 solution provides a stable wavelength-converted light output with reduced optical noise and speckle, achieving long-term stability and improved efficiency by dynamically adjusting the polarization and refractive index to compensate for fluctuations and maintain consistent light intensity.
Implementation Method 1
polarization adjusting means which is placed in an optical path of incident light and causes an output of the wavelength-converted light to change by changing its refractive index for a polarized component of the incident light
Implementation Method 2
produces second-harmonic light (257 or 244 nm) by wavelength conversion in an internal resonator
Implementation Method 3
produces a 198.5-nm continuous output by sum-frequency mixing between 244-nm light as the second harmonic of an argon-ion laser and 1064-nm light from an Nd:YAG laser
Data Source
AI summary
The invention is directed to the provision of a wavelength conversion-type ultraviolet light source apparatus that can obtain a stable output. A light source apparatus according to one mode of the invention includes: a laser light source 1 which produces fundamental light L1; at least one nonlinear optical crystal 3 which takes the fundamental light L1 or a harmonic thereof as incident light and outputs wavelength-converted light L2; and polarization adjusting means 2 which is placed in an optical path of the incident light and causes an output of the wavelength-converted light L2 to change by changing its refractive index for a polarized component of the incident light. The polarization adjusting means 2 changes the amount of change of the refractive index in accordance with an electrical signal output from a photodetector 7.