Pockels Cell Synchronization for SHG Timing Precision
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Solution Overview
Problem
Existing methods for measuring second harmonic generation (SHG) in semiconductor wafers face challenges with non-deterministic timing variations due to mechanical shutters and require continuous high voltage application with Pockels cells, leading to long-term drift and degradation, affecting signal integrity and repeatability.
Innovation Solution
A system that synchronizes optical excitation and detection using a precision signal generator to control a Pockels cell and mechanical shutter, eliminating timing delays and reducing high voltage application to only when necessary, thereby improving precision and stability.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If a mechanical shutter is used alone for switching light, then the system structure is simpler, but non-deterministic timing variations occur due to mechanical movement parts
Solution Approach 1:
The light switching function is segmented between two components: a Pockels cell for precise timing control and a mechanical shutter for blocking light. Each component performs a specific function, with the Pockels cell handling the precision timing aspect and the mechanical shutter handling the light blocking aspect, thereby achieving both simplicity and precision.
Solution Approach 2:
A controller acts as an intermediary that coordinates the Pockels cell and mechanical shutter. The controller receives timing signals and appropriately activates each component, ensuring that the Pockels cell switches light at precise moments while the mechanical shutter provides deterministic blocking, thereby resolving the timing precision issue.
2Measurement precision
If a Pockels cell is used alone for switching light, then timing precision is improved, but continuous high voltage application causes long-term drift and degradation
Solution Approach 1:
The Pockels cell is activated periodically only when precise light switching is needed, rather than continuously. The controller activates the Pockels cell at specific moments in the measurement cycle and deactivates it otherwise, allowing the system to maintain timing precision when required while avoiding continuous high voltage application that causes drift and degradation.
Solution Approach 2:
The continuous high voltage application requirement is extracted from the Pockels cell operation by introducing the mechanical shutter as a complementary component. The mechanical shutter handles the continuous light blocking function, allowing the Pockels cell to be turned off continuously and only activated periodically for precise timing, thereby eliminating the harmful continuous voltage effect.
3Illumination intensity
If the mechanical shutter is opened for a long period, then light transmission is sufficient, but light intensity increases gradually causing smearing of measured Io value
Solution Approach 1:
The gradual light intensity increase caused by the mechanical shutter's slow opening is replaced by the Pockels cell's instantaneous optical switching. The Pockels cell provides a sharp, deterministic light transmission transition that occurs much faster than the mechanical shutter can open, thereby eliminating the smearing effect while maintaining sufficient light transmission for accurate Io measurement.
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 enhances signal-to-noise ratio, stability, and repeatability by providing precise temporal alignment and reducing long-term drift, resulting in improved SHG measurement integrity.
Implementation Method 1
a Pockels cell (or another electro-optical switch) is added to the optical path between the light source (e.g., a laser) that illuminates the sample and the sample to block or allow transmission of light generated by the light source that is directed toward the sample
Implementation Method 2
a mechanical shutter may be added between the Pockels cell and the sample along the same optical path and in series with the Pockels cell
Implementation Method 3
an optical detector (e.g., a photodetector) and a pulse counter that is controlled separately, to allow for detection of SHG signals used to make EFISH measurements
Implementation Method 4
Second harmonic generation measurement in optical domain can be used to measure and characterize properties of dielectrics, semiconductors, and the corresponding interfaces based, for example, on Electric Field Induced Second Harmonic (EFISH) light generation
Data Source
AI summary
Methods are disclosed for improving one or more of jitter/timing, signal-to-noise ratio, signal integrity, stability, and repeatability of generation and measurement of Second Harmonic Generation (SHG) signals generated by a sample upon illumination by a light beam. The method may use precision hardware to control the generation of SHG signal and synchronize it with the optical detection process to improve the reliability and accuracy of measured SHG signals. A precise measurement of the initial SHG signal (Io) involves accurate temporal alignment between optical excitation and detection of the resulting SHG signal. Various disclosed systems and methods use high-speed Pockels Cell (PC) for controlling incident light, and precision electronics for synchronization.