Dr. Elharith M. Ahmed Profile

Dr. Elharith M. Ahmed

at SAIC

SPIE Involvement:

Author

Publications (4)

SPIE Journal Paper | 31 March 2022 Open Access

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

Elharith Ahmed, Gary Noojin, Michael Denton

JBO, Vol. 27, Issue 03, 035001, (March 2022) https://doi.org/10.1117/12.10.1117/1.JBO.27.3.035001

KEYWORDS: Laser damage threshold, Proteins, Cell death, Laser induced damage, Thermal modeling, Skin, Scanning electron microscopy, In vitro testing, Data modeling, Thermography

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Significance: Physics-based models supply simulated temperature rises to photothermal damage rate models and provide comprehensive risk assessments for laser-induced damage. As the physics-based models continue to be refined, the damage rate models have not advanced. This peculiar lack of improvement is counterintuitive considering the damage integral (Ω), originally derived for isothermal heating events, and fails to accurately represent the nonisothermal heating from short laser exposures. Aim: Derive a nonisothermal form of the damage integral and predict more accurately the damage induced by short laser exposures, as well as identify the role of heating rate in laser damage. Approach: From first principles, we derived a version of the damage integral specific to the shape of thermal profiles rather than the square function provided by Arrhenius plots. We used previously published threshold thermal profiles, where all nonisothermal frequency factors (Anon) solved all Ωnon values to unity. Nonisothermal correction factors correct isothermal Aiso values. Results: The Ea values were identical for both the isothermal and nonisothermal conventions. Correction factor values for Ωiso ranged from 0.0 (20-s exposures at thermal steady state) to −0.93 (0.05-s exposures). Based on empirical results, we have derived a two-dimensional empirical formula that predicts the heating rate as a function of exposure duration and ambient temperature. Threshold peak temperatures (Tpthr) and threshold critical temperatures are mathematically determined without thermal profiles when appropriate Ea and Anon values are established. Conclusions: We have identified a modified damage integral that does not rely on the Arrhenius plot and provides a value for the frequency factor (A) that accounts for the nonisothermal nature of short laser exposures. The method, validated in our in vitro retinal model, requires thermal profiles recorded under threshold conditions, such as at minimum visible lesions or the boundary of cell death. The method is a new option for laser damage modelers.

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SPIE Journal Paper | 22 June 2019 Open Access

Effect of ambient temperature and intracellular pigmentation on photothermal damage rate kinetics

Michael Denton, Elharith Ahmed, Gary Noojin, Amanda Tijerina, Giovanna Gamboa, Cherry Gonzalez, Benjamin Rockwell

JBO, Vol. 24, Issue 06, 065002, (June 2019) https://doi.org/10.1117/12.10.1117/1.JBO.24.6.065002

KEYWORDS: Laser damage threshold, Cell death, Cameras, Temperature metrology, Thermography, Absorption, In vitro testing, Tissues, Laser induced damage, Proteins

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Proceedings Article | 15 February 2017 Paper

Correlating measured transient temperature rises with damage rate processes in cultured cells

Michael Denton, Amanda Tijerina, Cherry Gonzalez, B. Giovana Gamboa, Gary Noojin, Elharith Ahmed, John Rickman, Phillip Dyer, Benjamin Rockwell

Proceedings Volume 10062, 100620I (2017) https://doi.org/10.1117/12.2250916

KEYWORDS: Temperature metrology, Cell death, Cameras, Microscopy, Thermodynamics, Photothermal interactions, Data modeling, Imaging systems, Calibration, Thermography, Tissues, Fiber lasers

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Proceedings Article | 7 March 2016 Paper

Photothermal damage is correlated to the delivery rate of time-integrated temperature

Michael Denton, Gary Noojin, B. Giovanna Gamboa, Elharith Ahmed, Benjamin Rockwell

Proceedings Volume 9706, 97061M (2016) https://doi.org/10.1117/12.2225024

KEYWORDS: Cell death, Cameras, Thermography, Temperature metrology, Tissues, Calibration, Proteins, Thermal modeling, Imaging systems, Absorption

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