Laser System Coherence Busting Mechanism for ASE Reduction
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Solution Overview
Problem
High power gas discharge laser systems for DUV light sources face challenges in maintaining beam quality and reducing ASE (Amplified Spontaneous Emission) while achieving high power output, particularly in immersion lithography and laser annealing applications, due to energy loss and coherence issues in existing oscillator-amplifier configurations.
Innovation Solution
A multi-chamber laser system with a seed laser oscillator and a ring power amplification stage, incorporating a coherence busting mechanism that uses a beam splitter and optical delay paths to separate and offset the seed laser output, reducing coherence and ASE, and featuring a power ring oscillator configuration with a partially reflecting output coupler to enhance energy stability and output power.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Power
If a conventional oscillator-amplifier configuration is used to achieve high power output, then power output is improved, but ASE (Amplified Spontaneous Emission) increases and beam quality deteriorates
Solution Approach 1:
The laser system is divided into multiple independent chambers (first chamber with seed oscillator, second chamber with ring power amplifier) to separate the oscillation and amplification processes spatially, allowing independent optimization of each stage to reduce ASE while maintaining high power output
Solution Approach 2:
A coherence busting mechanism using beam splitter and optical delay paths is introduced as an intermediary between the seed oscillator and ring power amplifier to reduce coherence and ASE before the beam enters the amplification stage
2Power
If high power output is achieved through existing configurations, then power is improved, but pulse-to-pulse stability deteriorates
Solution Approach 1:
The ring power amplifier configuration with partially reflecting output coupler creates a feedback mechanism that enhances energy stability and pulse-to-pulse consistency by allowing multiple passes through the gain medium, ensuring uniform energy distribution and reduced fluctuations
3Stability of the object's composition
If coherence is maintained in the laser beam, then beam quality is improved, but ASE increases and optical component life decreases
Solution Approach 1:
The coherence busting mechanism extracts and removes coherence from the laser beam using beam splitter and optical delay paths, separating the coherent seed beam into multiple paths with different delays, thereby reducing coherence and ASE while preserving sufficient beam quality for the application
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 achieves higher output power with reduced ASE and improved pulse-to-pulse stability, enabling better control over bandwidth and energy stability, and extends the life of optical components, thus addressing the limitations of existing systems in high power and high repetition rate applications.
Implementation Method 1
a beam splitter separating the seed laser output into a main beam and a beam entering an optical delay path
Implementation Method 2
a beam angular offset mechanism offsetting a delayed beam from the delay path and the main beam
Implementation Method 3
high power gas discharge laser systems for DUV light sources
Implementation Method 4
a laser amplification stage containing an amplifying gain medium in a second gas discharge excimer or molecular fluorine laser chamber receiving the output of the seed laser oscillator and amplifying the output
Data Source
AI summary
A method/apparatus may comprise a seed laser oscillator producing an output which may comprise: a first gas discharge excimer or molecular fluorine laser chamber; a line narrowing module within a first oscillator cavity; a laser amplification stage receiving the output of the seed laser oscillator which may comprise: a ring power amplification stage; a coherence busting mechanism intermediate the seed laser oscillator and the ring power amplification stage which may comprise a beam splitter separating the seed laser output into a main beam and a beam entering an optical delay path which may have a delay length longer than the coherence length of a pulse in the seed laser output and may have a beam angular offset mechanism offsetting a delayed beam and the main beam.