Calcium Fluoride Window Cushioning for Stress Birefringence

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Solution Overview

Problem

Chromatic aberration and reduced polarization purity in gas laser devices due to mechanical stress and thermal effects on calcium fluoride windows, leading to decreased laser beam quality and increased reflection losses.

Innovation Solution

Employing a cushioning member made of materials like 304 stainless steel, 303 stainless steel, 316 stainless steel, Hastelloy™ alloy, or Inconel™ with polished surfaces to reduce mechanical stress on the windows, ensuring high processing accuracy and maintaining polarization purity by preventing stress birefringence.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Reliability

If a holding member is used to sandwich and hold the calcium fluoride crystal window, then the window is securely fixed in position, but mechanical stress is applied to the window causing stress birefringence and reduced polarization purity

Engineering Contradiction:

Improvefixing stabilityVSAvoidstress birefringence

Core Design Contradiction:

ReliabilityVSObject-affected harmful factors

Solution Approach 1:

A cushioning member made of elastomeric material is introduced as an intermediary between the holding member and the calcium fluoride crystal window. This cushioning member acts as a stress-absorbing intermediary that prevents direct mechanical contact and stress transmission from the holding member to the window, thereby eliminating stress birefringence while maintaining secure fixation

Inventive Principle:

Principle #24Intermediary (Mediator)

Solution Approach 2:

The solution changes the mechanical parameters of the holding system by introducing a compliant elastomeric material with appropriate hardness and damping properties. This parameter change allows the system to maintain fixation stability while reducing mechanical stress on the optical window through the elastomeric material's ability to deform and absorb stress

Inventive Principle:

Principle #35Parameter changes

2Productivity

If the laser output power is increased to enhance productivity, then more thermal effects are generated causing increased stress birefringence and polarization degradation

Engineering Contradiction:

Improvelaser output powerVSAvoidthermal stress birefringence

Core Design Contradiction:

ProductivityVSObject-affected harmful factors

Solution Approach 1:

The elastomeric cushioning member is installed beforehand to provide preemptive stress protection. This cushioning element is positioned in advance to absorb and distribute thermal expansion stresses before they can cause significant birefringence in the window, enabling higher output power operation with minimal polarization degradation

Inventive Principle:

Principle #11Beforehand cushioning (Prior cushioning)

Solution Approach 2:

The solution accounts for thermal expansion effects by using an elastomeric material that can accommodate dimensional changes in the holding member and window assembly during high-power operation. The cushioning member's compliance allows it to absorb thermal expansion stresses without transmitting them to the optical window

Inventive Principle:

Principle #37Thermal expansion

3Ease of manufacture

If conventional materials are used for the cushioning member, then manufacturing is easier, but the material may react with laser gas or degrade under high-power laser conditions

Engineering Contradiction:

Improvematerial availabilityVSAvoidchemical stability

Core Design Contradiction:

Ease of manufactureVSReliability

Solution Approach 1:

The elastomeric material is selected to create a chemically inert environment between the metal holding member and the laser gas. The cushioning member's inert properties prevent chemical reactions with reactive laser gases while maintaining mechanical functionality, ensuring long-term reliability in the high-power laser environment

Inventive Principle:

Principle #39Inert atmosphere (Inert environment)

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 solution effectively minimizes stress-induced birefringence and maintains high polarization purity even at higher laser output levels, enhancing the quality and efficiency of the laser beam output.

Implementation Method 1

a seal member provided between the holding member and one surface of the optical element in close contact therewith

Methodology Applied

Scientific EffectVacuum sealing:

Implementation Method 2

a cushioning member provided between the holding member and the other surface of the optical element in contact therewith

Methodology Applied

Scientific EffectStress reduction:

Implementation Method 3

a plate-like optical element made of a calcium fluoride crystal

Methodology Applied

Scientific EffectOptical transmission:

Implementation Method 4

chromatic aberration and reduced polarization purity in gas laser devices due to mechanical stress and thermal effects on calcium fluoride windows

Methodology Applied

Scientific EffectBirefringence: Birefringence

Data Source

PatentUS9093814B2Optical device, and laser chamber and gas laser apparatus using the same

Publication Date: 2015.07.28 GIGAPHOTON INC

AI summary

An optical device includes a plate-like optical element made of a calcium fluoride crystal, a holding member to sandwich and hold the optical element, a seal member provided between the holding member and one surface of the optical element in close contact therewith, and a cushioning member provided between the holding member and the other surface of the optical element in contact therewith. The cushioning member is made of one of a 304 stainless steel, a 303 stainless steel, a 316 stainless steel, a Hastelloy™ alloy, a carbon steel for machine construction S45C, and Inconel™.