Transient Ellipsometry Using ASOPS for Fast Vibration-Free Sampling
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Solution Overview
Problem
Optical metrology devices using mechanical optical delay lines for transient ellipsometry are slow, prone to vibrations, and costly due to the use of lock-in amplifiers, limiting throughput and increasing expenses.
Innovation Solution
Implement asynchronous optical sampling (ASOPS) using lasers with different pulse repetition rates to generate varying time delays between pump and probe pulses, eliminating the need for mechanical delay lines and reducing system complexity.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Speed
If mechanical optical delay lines are used for transient ellipsometry, then time delay control is achieved, but the system becomes slow and prone to vibrations
Solution Approach 1:
The patent replaces mechanical optical delay lines with an asynchronous optical sampling system using two mode-locked lasers with slightly different repetition rates. This substitution eliminates mechanical moving parts that cause vibrations and slow response, using instead the temporal beating between the two laser frequencies to achieve the same time-delay scanning function through optical rather than mechanical means.
2Measurement precision
If mechanical delay stages are used, then time resolution is achieved, but vibrations are introduced
Solution Approach 1:
The invention substitutes mechanical delay stages with a fully optical asynchronous sampling approach. Two mode-locked lasers operating at slightly different repetition rates create a temporal beat pattern that provides precise time resolution without any mechanical movement, thereby eliminating vibration-induced measurement errors while maintaining high time resolution capability.
3Measurement precision
If lock-in amplifiers are used, then signal detection is improved, but costs increase
Solution Approach 1:
The asynchronous optical sampling system generates its own time-resolution signal through the inherent temporal beating between the two mode-locked lasers with different repetition rates. This self-generated timing reference eliminates the need for external lock-in amplifiers or complex synchronization electronics, reducing system cost while maintaining signal detection capability through direct temporal gating of the detector signals.
4Productivity
If mechanical optical delay lines are used, then transient ellipsometry measurements are obtained, but throughput is limited
Solution Approach 1:
The patent enables continuous measurement throughput by using two continuously operating mode-locked lasers with slightly different repetition rates. The asynchronous sampling approach allows data collection at every laser pulse without requiring mechanical repositioning between measurements, creating a continuous measurement stream that maximizes productivity while minimizing measurement time through uninterrupted data acquisition.
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
Enhances throughput, minimizes vibrations, and lowers costs by using synchronized laser pulses to perform transient ellipsometry without mechanical delay stages, enabling fast data collection and accurate material characterization.
Implementation Method 1
The pump pulses generate transient perturbations in the sample material
Implementation Method 2
reflected probe pulses are modulated in response to the transient perturbation in the sample material
Implementation Method 3
the polarization change of polarized incident light due to sample materials and geometries is measured from the reflected light
Data Source
AI summary
An optical metrology device configured for transient ellipsometry includes a light source with at least one laser, that generates pump pulses at a first pulse repetition rate and probe pulses at a second, different, pulse repetition rate that produces a varying time delay between the pump pulses and the probe pulses. The pump pulses generate transient perturbations in the sample material and reflected probe pulses are modulated in response to the transient perturbation in the sample material based on the varying time delay. A polarization state generator generates a polarization state in the probe pulses and a polarization state analyzer analyzes the reflected probe pulses from the sample, which is received by a detector. Transient ellipsometric measurements are generated from the reflected probe pulses at a plurality of time delays between the pump pulses and probe pulses.