Phase-Modulated OPA Laser for Temporal Coherence Reduction
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Solution Overview
Problem
Existing semiconductor manufacturing laser systems face issues such as short laser life, corrosiveness, health hazards, and fiber nonlinearity, particularly in ArF lasers and solid-state alternatives, which affect spatial coherence and temporal incoherence, leading to speckle noise and high costs.
Innovation Solution
A laser system with a seed laser, phase modulator, and optical parametric amplifier (OPA) is used to control temporal coherence by phase modulation and spectral broadening, reducing speckle noise through an OPA pumped by a pulsed laser, utilizing nonlinear optical effects and harmonic generators to achieve desired wavelengths.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Use of energy by moving object
If ArF laser is used for semiconductor manufacturing, then 193.4 nm wavelength and 6 kHz pulse repetition rate are achieved, but short laser life and corrosive characteristics occur
Solution Approach 1:
The patent transitions from ArF laser technology to a solid-state laser system operating at 1.547 μm wavelength, fundamentally changing the operating parameters including wavelength, pulse repetition rate (up to 100 kHz), and output energy characteristics. This parameter change eliminates the short life and corrosiveness issues inherent to ArF lasers while maintaining the required 193.4 nm wavelength through harmonic generation.
2Power
If fiber amplifier is used to amplify pulsed diode laser, then amplification is achieved, but fiber nonlinearity occurs with high peak power
Solution Approach 1:
The patent introduces a Raman amplifier as an intermediary stage between the pulsed diode laser and the final output. The Raman amplifier uses stimulated Raman scattering to transfer energy from a pump laser to the signal laser, enabling high power amplification without the nonlinear effects that plague direct fiber amplification. This intermediary approach allows achieving mJ-class output energy while avoiding fiber nonlinearity.
3Object-affected harmful factors
If temporal coherence is reduced in laser system, then speckle noise is reduced and illumination uniformity is improved, but laser performance may be affected
Solution Approach 1:
The patent employs dynamic control of temporal coherence through adjustable dispersion elements and modulators in the laser cavity. By dynamically adjusting the coherence properties, the system can optimize between speckle noise reduction and laser performance requirements for different applications, allowing adaptability rather than a fixed compromise.
4Adaptability or versatility
If solid-state approach is used to amplify pulsed diode laser at 1.547 μm, then alternative to ArF laser is provided, but limitations occur in reaching 193.4 nm through eighth harmonic
Solution Approach 1:
The patent segments the wavelength conversion process into multiple stages: direct generation of 1.547 μm fundamental wavelength, followed by separate harmonic generation stages to reach 193.4 nm. This segmented approach allows optimization of each stage independently, improving overall wavelength conversion precision while maintaining the adaptability of the solid-state platform.
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 system provides improved laser sources with reduced temporal coherence and speckle noise, enabling high-resolution imaging with uniform illumination and efficient wavelength conversion to narrowband UV ranges.
Implementation Method 1
a phase modulator positioned to receive laser light from the seed laser and to impart phase modulation thereto
Implementation Method 2
an optical parametric amplifier positioned to receive phase-modulated laser light at one of its inputs and a pump laser light at another input, and to produce an output beam having spectral characteristics of the phase-modulated laser light that is amplified in accordance with a temporal feature of the pump laser light
Data Source
AI summary
Methods, systems and methods for reducing temporal coherence of laser systems are described. One example laser system includes a seed laser having a continuous wave output and operable at a first wavelength, a phase modulator positioned to receive laser light from the seed laser and to impart phase modulation to the seed laser. The laser system also includes an optical parametric amplifier positioned to receive phase-modulated laser light at one of its inputs and a pump laser light at another input, and to produce an output beam having spectral characteristics of the phase-modulated laser light that is amplified according to a temporal feature of the pump laser light. In the example laser system, an output of the optical parametric amplifier has a lower temporal coherence compared to the seed laser.