Nonlinear Crystal Segmentation for UV Laser Surface Damage

Resolve Bottlenecks,
Find Innovative SolutionsGenerate Solutions

Solution Overview

Problem

Nonlinear crystals used for frequency conversion suffer from surface damage when exposed to high-intensity ultraviolet radiation, limiting the reliability of high-power laser systems due to their lower damage threshold compared to lower frequency laser radiation.

Innovation Solution

A nonlinear crystal is configured with a phase-matching portion for efficient frequency conversion and a phase-mismatching portion to reduce light intensity on the exit face, achieved by extending the crystal length while maintaining phase matching in the first portion and inducing phase mismatching in the second portion, which increases the beam diameter and reduces intensity on the exit surface.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Productivity

If the nonlinear crystal length is extended to improve frequency conversion efficiency, then conversion efficiency increases, but light intensity on the exit face increases causing surface damage

Engineering Contradiction:

Improvefrequency conversion efficiencyVSAvoidsurface damage from UV radiation

Core Design Contradiction:

ProductivityVSObject-affected harmful factors

Solution Approach 1:

The nonlinear crystal is divided into two distinct portions: a first portion with phase-matching conditions for efficient frequency conversion, and a second portion with phase-mismatching conditions that act as an output coupler. This segmentation allows the crystal to simultaneously achieve high conversion efficiency while reducing exit face intensity through the phase-mismatched section.

Inventive Principle:

Principle #1Segmentation

Solution Approach 2:

Different portions of the nonlinear crystal are assigned different optical properties: the first portion is optimized for phase-matching to maximize conversion efficiency, while the second portion is designed with phase-mismatching characteristics to reduce the intensity of light exiting the crystal. This local differentiation of properties resolves the contradiction between efficiency and surface damage.

Inventive Principle:

Principle #3Local quality

2Power

If high power fundamental laser is used to increase brightness, then laser power increases, but nonlinear crystal surface damage threshold is exceeded

Engineering Contradiction:

Improvelaser powerVSAvoidcrystal reliability

Core Design Contradiction:

PowerVSReliability

Solution Approach 1:

The crystal is segmented into phase-matching and phase-mismatching portions, where the second portion serves as an output coupler that reduces the intensity of light exiting the crystal. This allows high power fundamental laser to be used without exceeding the damage threshold of the nonlinear crystal surface.

Inventive Principle:

Principle #1Segmentation

Solution Approach 2:

The phase-mismatched second portion of the crystal acts as an intermediary element that mediates between the high power input and the crystal's damage threshold. It provides a transition zone that reduces the intensity of frequency-converted light before it exits, protecting the crystal surface from damage.

Inventive Principle:

Principle #24Intermediary (Mediator)

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 approach significantly reduces surface damage by decreasing the light intensity on the exit face, extending the life of high-power ultraviolet harmonic generation systems and maintaining beam quality and conversion efficiency.

Implementation Method 1

Optical nonlinear crystals are extensively used for frequency conversion of a fundamental laser wavelength to a new wavelength. Examples include conversion of 1064 nm light from neodymium-doped yttrium aluminium garnet (Nd:YAG) lasers to a wavelength of 532 nm using nonlinear crystals

Methodology Applied

Scientific EffectNonlinear optical frequency conversion: Second Harmonic Generation

Implementation Method 2

the first length portion of the nonlinear crystal is phase matching for the input light and the frequency converted light

Methodology Applied

Scientific EffectPhase matching:

Implementation Method 3

the second length portion of the nonlinear crystal is phase mismatching for the input light and the frequency converted light

Methodology Applied

Scientific EffectPhase mismatching:

Implementation Method 4

a phase mismatcher disposed in proximity to the second length portion of the nonlinear crystal for changing a refractive index and enabling phase mismatching

Methodology Applied

Scientific EffectRefractive index change:

Data Source

PatentUS8243764B2Frequency conversion of a laser beam using a partially phase-mismatched nonlinear crystal

Publication Date: 2012.08.14 WELLS FARGO BANK NA

AI summary

The invention relates to a laser system including a nonlinear crystal having a first length portion and a second length portion. The nonlinear crystal disposed to receive input light from the laser for converting the input light into frequency converted light; wherein the nonlinear crystal is configured so that the first length portion of the nonlinear crystal is phase matching for the input light and the frequency converted light, and the second length portion of the nonlinear crystal is phase mismatching for the input light and the frequency converted light. Phase mismatching means may include a temperature controlling board, a clamp, or electrodes.