Alkali Halide Crystal Grading via UV Fluorescence
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Solution Overview
Problem
Current methods fail to provide a quantitative evaluation of non-intrinsic absorption in optical materials, particularly for high-energy density applications, leading to quality losses and inefficiencies in photolithography due to heating and fluorescence effects.
Innovation Solution
A method involving fluorescence measurements at ultraviolet wavelengths to determine radiation-dependent transmission by analyzing the slope of transmission versus fluence, using normalized fluorescence intensities to quantify non-linear absorption and grade alkali or alkaline earth halide single crystals for optical components.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If fluorescence measurements are performed after a waiting time of 50 nsec after the laser pulse ends, then fluorescence values can be obtained, but these values cannot be used for quality control and determination of impurities
Solution Approach 1:
The patent applies preliminary action by performing fluorescence measurements during the laser pulse or immediately after its termination, before the fluorescence signal decays to unusable levels. This timing approach captures the fluorescence signal while it still contains information about impurities and material quality, enabling both measurement capability and reliable quality control to coexist.
2Ease of manufacture
If crystals with comparatively high impurity content are used for fluorescence measurement, then fluorescence values can be obtained, but these crystals are not suitable for stringent requirements of photolithography
Solution Approach 1:
The patent uses an intermediary approach by measuring fluorescence during the laser pulse or immediately after termination, capturing the signal before it decays. This timing strategy acts as an intermediary that preserves the correlation between fluorescence intensity and impurity content, allowing high-quality crystals to be measured effectively without requiring deliberately impure materials.
Solution Approach 2:
The patent replaces the conventional approach of using highly impure crystals for measurement with a timing-based solution that enables measurement of high-quality crystals. By substituting the measurement timing strategy rather than the material composition, the system achieves both measurement feasibility and high material quality.
3Loss of energy
If absorption is kept as small as possible for optical systems, then transmission is improved, but heating effects and fluorescence still cause quality losses
Solution Approach 1:
The patent applies feedback by measuring fluorescence during or immediately after the laser pulse, using the fluorescence signal as real-time information about the material's absorption characteristics and impurity content. This feedback mechanism enables quality control and selection of materials with minimal harmful effects, improving both transmission and reducing heating and fluorescence-related quality losses.
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
Enables accurate quantitative assessment and grading of optical materials for high-energy applications, improving transmission and reducing heating effects, thus enhancing the quality and suitability of materials for photolithography and other applications.
Implementation Method 1
materials for optical components absorb more or less radiation passing through them
Implementation Method 2
Energy, which leads to heating, is added to the optical material by both the intrinsic and also the non-intrinsic absorption
Implementation Method 3
In many materials however a part of the absorbed radiation is not only converted into heat, but also into a form of fluorescence
Data Source
AI summary
A method is described for quantitative determination of suitability of an optical material, especially alkali halide and alkaline earth halide single crystals, for optical components exposed to high energy densities, especially of pulsed laser light at wavelengths under 250 nm. In this procedure radiation-dependent transmission of the optical material is determined at ultraviolet wavelengths by fluorescence measurements for fluorescence induced by ultraviolet radiation at these ultraviolet wavelengths. This is accomplished by a method including determining an induced fluorescence maximum of a non-linear absorption process, measuring a slope (|dT/dH|) of a functional relationship representing the dependence of the radiation-dependent transmission on fluence (H) for the induced fluorescence and determining radiation-dependent transmissions from this slope for particular fluence values.