Mid-IR Laser Harmonic Generation for Composite Ultrasound Inspection

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Solution Overview

Problem

Current laser ultrasonic detection systems for composite materials have limited energy and repetition rate, restricting their ability to effectively inspect composite components for defects like cracks and delaminations.

Innovation Solution

A system utilizing a CO2 laser to generate harmonics, producing a high-energy mid-range infrared laser beam with increased energy levels (at least 50 milli-Joules) and frequency (at least 200 Hz) for thermo-elastically exciting composite surfaces, enhancing ultrasonic displacement measurements without surface damage.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Measurement precision

If a CO2 laser is used to generate ultrasonic vibrations for inspecting composite materials, then the detection capability for defects is improved, but the energy level and repetition rate remain limited

Engineering Contradiction:

Improvedetection capabilityVSAvoidenergy level

Core Design Contradiction:

Measurement precisionVSUse of energy by moving object

Solution Approach 1:

The patent transforms the laser wavelength parameter from 10.6 microns (CO2 laser) to 3.2 microns (harmonic generation), which fundamentally changes the energy characteristics and interaction with composite materials. This parameter change enables both higher energy levels and improved detection precision simultaneously.

Inventive Principle:

Principle #35Parameter changes

Solution Approach 2:

The patent replaces the direct mechanical vibration approach with optical field-based ultrasonic generation. By using laser-induced thermoelastic expansion, the system generates ultrasonic vibrations optically rather than mechanically, enabling higher energy levels and repetition rates.

Inventive Principle:

Principle #28Mechanics substitution (Replace mechanical system)

2Measurement precision

If higher energy laser beams are used to increase ultrasonic displacement amplitude, then the detection sensitivity is improved, but the risk of composite surface damage increases

Engineering Contradiction:

Improvedetection sensitivityVSAvoidsurface damage risk

Core Design Contradiction:

Measurement precisionVSObject-affected harmful factors

Solution Approach 1:

The patent changes the laser wavelength from 10.6 microns to 3.2 microns through harmonic generation. This parameter change reduces photon energy while maintaining high beam intensity, enabling high detection sensitivity without causing surface damage to the composite material.

Inventive Principle:

Principle #35Parameter changes

Solution Approach 2:

The patent uses pulsed laser operation with optimized pulse duration and repetition rate. The periodic pulsed action allows the composite material to cool between pulses, preventing cumulative thermal damage while maintaining high detection sensitivity through controlled thermal expansion.

Inventive Principle:

Principle #19Periodic action

3Productivity

If the laser repetition rate is increased to improve inspection efficiency, then the productivity is improved, but the energy per pulse decreases

Engineering Contradiction:

Improveinspection efficiencyVSAvoidenergy per pulse

Core Design Contradiction:

ProductivityVSUse of energy by moving object

Solution Approach 1:

The patent changes the laser operating parameters by generating harmonics at 3.2 microns, which enables higher repetition rates while maintaining adequate energy per pulse. The different wavelength characteristics allow for optimized pulse parameters that support both high productivity and sufficient energy delivery.

Inventive Principle:

Principle #35Parameter changes

Solution Approach 2:

The patent replaces conventional laser operation with harmonic generation, which fundamentally changes the energy delivery characteristics. This substitution enables high repetition rate operation with maintained pulse energy, improving inspection efficiency without sacrificing detection capability.

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 system provides higher amplitude displacements and precision in testing data, reducing the risk of composite surface damage while enabling more effective detection of defects in composite materials.

Implementation Method 1

producing a harmonic of the CO2 laser beam

Methodology Applied

Scientific EffectHarmonic generation: Second Harmonic Generation

Implementation Method 2

thermo-elastically exciting a surface of the target object to produce ultrasonic displacements on the target object

Methodology Applied

Scientific EffectThermoelastic effect: Thermal Expansion

Data Source

PatentUS8113056B2Mid-IR laser for generation of ultrasound using a CO2 laser and harmonic generation

Publication Date: 2012.02.14 LOCKHEED MARTIN CORP

AI summary

A mid infrared range laser source for ultrasound inspection having a high energy laser coupled with one or more harmonic generation devices. The high energy laser may be a CO2 laser and tuned to emit laser light at a single wavelength. The harmonic generation devices convert the laser beam into the mid infrared range for optimal ultrasound inspection.