Optical Frequency Converter for Laser Sustained Plasma Pumping

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Solution Overview

Problem

High-power laser sustained plasmas (LSPs) pumped in the infrared (IR) spectral range tend to have larger sizes due to stronger absorption at high temperatures, limiting the maximum spectral radiance and temperature that can be achieved, as few high-power lasers are available in the visible (VIS) spectral range, restricting the application of VIS lasers for pumping LSPs.

Innovation Solution

A system utilizing an optical frequency converter to generate broadband illumination by frequency converting the illumination source from a first spectral frequency to a second, different spectral frequency, which is directed to a plasma forming material to produce a smaller, brighter plasma with higher temperature and reduced absorptivity, thereby overcoming the limitations of IR pumping.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Power

If infrared laser is used to pump LSP, then high power can be achieved, but plasma size increases and temperature is limited

Engineering Contradiction:

Improvepump powerVSAvoidplasma temperature

Core Design Contradiction:

PowerVSTemperature

Solution Approach 1:

The patent changes the spectral frequency parameter of the pump laser from infrared to visible range. This parameter change reduces plasma absorption coefficient, allowing high power pumping while maintaining smaller plasma size and higher temperatures. The visible wavelength laser (e.g., 532nm) creates plasma with lower absorptivity compared to infrared laser, resolving the contradiction between achieving high power and maintaining high temperature.

Inventive Principle:

Principle #35Parameter changes

2Power

If infrared laser is used to pump LSP, then high power can be achieved, but spectral radiance is limited due to plasma growth

Engineering Contradiction:

Improvepump powerVSAvoidspectral radiance

Core Design Contradiction:

PowerVSIllumination intensity

Solution Approach 1:

The patent changes the pump laser wavelength from infrared to visible range, which fundamentally alters plasma absorption characteristics. This parameter change prevents plasma from growing in size while being pumped at high power, thereby maintaining high spectral radiance. The visible wavelength laser creates a more confined plasma with higher energy density, resolving the contradiction between high power and high spectral radiance.

Inventive Principle:

Principle #35Parameter changes

3Volume of moving object

If visible laser is used to pump LSP, then smaller plasma size can be achieved, but few high-power lasers are available

Engineering Contradiction:

Improveplasma volumeVSAvoidlaser availability

Core Design Contradiction:

Volume of moving objectVSEase of manufacture

Solution Approach 1:

The patent uses an optical frequency converter (frequency doubling crystal) as an intermediary device. The system takes an available infrared laser and converts its output to visible wavelength through frequency doubling. This intermediary approach makes visible wavelength pumping practically available by transforming the output of commonly available infrared lasers, resolving the contradiction between achieving small plasma volume and laser availability.

Inventive Principle:

Principle #24Intermediary (Mediator)

Solution Approach 2:

The patent replaces the need for direct visible laser generation with an optical frequency conversion system. Instead of requiring a native visible laser source, the system substitutes an infrared laser combined with a frequency doubling crystal. This substitution leverages the availability of infrared laser technology while achieving the desired visible wavelength pumping, making the system more practically implementable.

Inventive Principle:

Principle #28Mechanics substitution (Replace mechanical system)

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 frequency conversion results in a smaller, brighter plasma with higher temperature and improved spectral radiance, as the converted illumination has lower absorption at the plasma edge and center, enhancing the plasma's ability to emit broadband illumination.

Implementation Method 1

an optical frequency converter configured to receive the illumination having the first spectral frequency from the illumination source and configured to output pump illumination having a second spectral frequency that is different from the first spectral frequency

Methodology Applied

Scientific EffectOptical frequency conversion: Second Harmonic Generation

Implementation Method 2

the pump illumination causes the plasma forming material to form a plasma

Methodology Applied

Scientific EffectOptical absorption: Absorption (EM radiation)

Data Source

PatentUS10568195B2System and method for pumping laser sustained plasma with a frequency converted illumination source

Publication Date: 2020.02.18 KLA CORP

AI summary

A system for generating pump illumination for laser sustained plasma (LSP) is disclosed. In embodiments, the system includes an illumination source configured to output illumination having a first spectral frequency and an optical frequency converter. The optical frequency converter can be configured to receive the illumination having the first spectral frequency from the illumination source and configured to output pump illumination having a second spectral frequency that is different from the first spectral frequency.