Ring Power Amplification Stage for DUV Laser 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) due to energy loss-prone input coupling and unacceptable levels of ASE in existing oscillator-based amplification systems, which affect the coherence and stability of the laser output.
Innovation Solution
A ring power amplification stage with a partially reflecting optical element and an optical delay path longer than the coherence length of the seed laser oscillator output, combined with a coherence busting mechanism, is used to inject the seed laser output into the ring power amplification stage, reducing ASE and improving pulse-to-pulse stability while maintaining optimized beam parameters.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Power
If an oscillator-based amplification system is used to increase output power, then power amplification is achieved, but ASE (Amplified Spontaneous Emission) increases and beam coherence deteriorates
Solution Approach 1:
The patent extracts the harmful oscillation feedback loop by using a ring cavity configuration with unidirectional light propagation. The optical diode (Faraday rotator + polarizing beam splitter) removes the backward reflection path that causes ASE buildup, effectively taking out the harmful feedback mechanism while preserving forward amplification.
Solution Approach 2:
The patent introduces an optical diode as an intermediary component between the seed laser and the amplification medium. This intermediary allows unidirectional light transmission, enabling power amplification while blocking the reverse path that would otherwise generate harmful ASE.
2Power
If conventional input coupling is used in oscillator systems, then amplification is achieved, but energy loss increases and pulse-to-pulse stability deteriorates
Solution Approach 1:
The patent replaces conventional mechanical/optical input coupling methods with direct injection seeding into the ring cavity. The seed laser beam is coupled directly into the amplification medium through the optical diode without requiring high-reflectivity mirrors or complex coupling optics, thereby reducing energy loss and improving stability.
3Power
If oscillator-based amplification is used to increase output power, then power is improved, but pulse energy stability worsens
Solution Approach 1:
The patent removes the oscillation feedback mechanism that causes pulse-to-pulse energy fluctuations. By using unidirectional ring cavity amplification without mirrors to reflect light back into the gain medium, the system eliminates the build-up of spontaneous emission and the associated energy instability between pulses.
4Power
If existing amplification systems are used, then output power is achieved, but LNM (Laser Narrowing Module) life decreases due to higher energy loss
Solution Approach 1:
The patent converts the potential harm of high-energy laser operation into a benefit by using the ring cavity configuration to achieve efficient amplification with minimal energy loss. The unidirectional propagation reduces wasted energy, thereby extending the life of energy-sensitive components like the LNM while maintaining high output power.
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 configuration achieves higher output power with reduced ASE, improved pulse energy stability, and extended LNM (Laser Narrowing Module) life, enabling higher repetition rates and lower costs of operation while maintaining or increasing output power.
Implementation Method 1
a seed laser oscillator producing an output comprising a laser output light beam
Implementation Method 2
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
Implementation Method 3
a coherence busting mechanism intermediate the seed laser oscillator and the ring power amplification stage comprising an optical delay path having a delay length longer than the coherence length
Data Source
AI summary
A method and apparatus may comprise a line narrowed pulsed excimer or molecular fluorine gas discharge laser system which may comprise a seed laser oscillator producing an output comprising a laser output light beam of pulses 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 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 of the seed laser oscillator to form a laser system output comprising a laser output light beam of pulses, which may comprise a ring power amplification stage.