Damage integral and other predictive formulas for nonisothermal heating during laser exposure

Area of Science:

• Biomedical Optics
• Laser-Material Interactions
• Photothermal Damage Modeling

Background:

• Current physics-based models for laser-induced damage rely on damage rate models that have not advanced.
• The conventional damage integral (Ω) is derived for isothermal heating and inaccurately represents non-isothermal heating from short laser exposures.
• This limits the comprehensive risk assessment of laser-induced damage.

Purpose of the Study:

• Derive a non-isothermal damage integral to accurately predict damage from short laser exposures.
• Identify the role of heating rate in laser damage.
• Provide a refined model for laser damage assessment.

Main Methods:

• Derived a modified damage integral based on thermal profile shapes, moving beyond the limitations of Arrhenius plots.
• Utilized previously published threshold thermal profiles to solve non-isothermal frequency factors (Anon).
• Developed a two-dimensional empirical formula to predict heating rate based on exposure duration and ambient temperature.

Main Results:

• Identified identical activation energy (Ea) values for both isothermal and non-isothermal models.
• Correction factor values for the isothermal damage integral (Ωiso) ranged from 0.0 to -0.93.
• Established a method to mathematically determine threshold peak and critical temperatures without thermal profiles.

Conclusions:

• Developed a modified damage integral that accounts for the non-isothermal nature of short laser exposures.
• Validated the method using an in vitro retinal model with threshold condition thermal profiles.
• The new model offers a valuable alternative for laser damage modelers.