Ring Cavity Pulse Multiplier for UV Laser Repetition Rate
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Solution Overview
Problem
Current semiconductor inspection and metrology systems face challenges with UV laser systems, as high repetition rate modifications are costly and reduce peak power, limiting the efficiency of frequency conversion and overall power levels.
Innovation Solution
A pulse multiplier system using a ring cavity with a beam splitter and mirrors to split and recirculate laser pulses, increasing repetition rate while reducing peak power and maintaining equal energy in each pulse, allowing for high-speed inspection and metrology with off-the-shelf lasers.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Speed
If the repetition rate of a UV laser is increased by modifying the laser medium, pump system, and/or driving electronics, then the repetition rate is improved, but the cost and complexity of the system increase significantly and the peak power per pulse decreases
Solution Approach 1:
The invention segments a single high-energy laser pulse into multiple lower-energy pulses using a ring cavity with beam splitters and mirrors. This segmentation approach increases the effective repetition rate without requiring modifications to the laser medium, pump system, or driving electronics, thereby avoiding the associated cost and complexity increases.
Solution Approach 2:
The ring cavity acts as an intermediary system between the laser source and the sample. It takes a single input pulse and generates multiple output pulses through controlled reflections and beam splitting, effectively multiplying the repetition rate without directly modifying the laser subsystem itself.
2Measurement precision
If the repetition rate of the fundamental laser in a UV laser is increased, then more pulses are collected per data acquisition leading to better signal-to-noise ratios, but the peak power of the fundamental decreases reducing the efficiency of frequency conversion
Solution Approach 1:
By segmenting a single high-peak-power pulse into multiple pulses within the ring cavity, the system maintains adequate peak power for efficient frequency conversion while increasing the number of pulses available for data acquisition. This segmentation allows multiple pulses to be collected per input pulse, improving signal-to-noise ratios without sacrificing peak power.
Solution Approach 2:
The ring cavity creates a periodic sequence of pulses from a single input pulse through controlled reflections and beam splitting. This periodic action generates multiple output pulses at regular intervals, enabling better averaging and improved signal-to-noise ratios while the original high peak power is preserved in each segmented pulse.
3Reliability
If a pulsed laser with high repetition rate and wide pulse width is used to achieve sufficient time-averaged radiance, then the instantaneous peak power per pulse is reduced, but this results in less damage to optics and sample while the complexity of achieving high average UV power levels increases
Solution Approach 1:
The ring cavity segments a single high-peak-power pulse into multiple pulses, effectively creating a high repetition rate output without requiring a fundamentally different laser system. This segmentation achieves the reliability benefit of reduced peak power damage mechanisms while avoiding the complexity of redesigning the entire laser subsystem.
Solution Approach 2:
The ring cavity creates multiple copies of the original laser pulse through controlled reflections and beam splitting. Each copy has reduced peak power compared to the original, providing the damage reduction benefit while the entire process is achieved through passive optical components rather than complex active laser modifications.
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 pulse multiplier effectively doubles the repetition rate of UV laser systems while minimizing peak power, enabling efficient high-speed inspection and metrology with minimal energy loss, and can be integrated into various inspection and metrology systems.
Implementation Method 1
A pulse multiplier system using a ring cavity with a beam splitter and mirrors to split and recirculate laser pulses
Implementation Method 2
using a beam splitter and one or more mirrors to generate an optimized pulse multiplier
Data Source
Figure 1A
Figure 1B
Figure 1C
AI summary
A pulse multiplier includes a beam splitter and one or more mirrors. The beam splitter receives a series of input laser pulses and directs part of the energy of each pulse into a ring cavity. After circulating around the ring cavity, part of the pulse energy leaves the ring cavity through the beam splitter and part of the energy is recirculated. By selecting the ring cavity optical path length, the repetition rate of an output series of laser pulses can be made to be a multiple of the input repetition rate. The relative energies of the output pulses can be controlled by choosing the transmission and reflection coefficients of the beam splitter. This pulse multiplier can inexpensively reduce the peak power per pulse while increasing the number of pulses per second with minimal total power loss.