How to calculate the temperature change of a laser-irradiated material

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Discussion Overview

The discussion focuses on calculating the temperature change of a material exposed to a laser pulse, considering factors such as optical absorption, reflection, transmission, and thermal relaxation times. Participants explore theoretical and experimental aspects of this problem, including energy flow and potential ablation effects.

Discussion Character

  • Exploratory
  • Technical explanation
  • Conceptual clarification
  • Debate/contested
  • Experimental/applied

Main Points Raised

  • One participant seeks to calculate the temperature change from a laser pulse, noting the need for approximations regarding thermal relaxation times and energy conversion.
  • Another participant suggests drawing a diagram to illustrate energy flow from the laser to thermal and chemical products.
  • There is a question about whether the discussion pertains to a pulse or a continuous laser beam, which is clarified to be a pulse with a width of approximately 6ns.
  • Concerns are raised about the high peak power delivered to the sample during the pulse, with implications for potential ablation and the need to consider latent heat in temperature calculations.
  • Further advice is given to start with a diagram showing energy flow into the sample and losses due to ablation and conduction.

Areas of Agreement / Disagreement

Participants generally agree on the need to consider various energy flows and the potential for ablation, but there are differing views on the specifics of the calculations and the implications of the pulse duration.

Contextual Notes

Limitations include assumptions about thermal relaxation times, the completeness of energy conversion, and the specific conditions under which ablation occurs. The discussion does not resolve these uncertainties.

jgk5141
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TL;DR
How to calculate the temperature change of a laser-irradiated material when the absorption, laser pulse energy, spot size, wavelength, pulse width, and frequency are known?
I am looking to approximately calculate the temperature change of a sample that was exposed to a laser pulse. Experimentally, we know the optical absorption, reflection, and transmission, as well as the source parameters for our laser system. I realize that I will have to make approximations about the thermal relaxation times, optical absorption mechanisms, and the fact that the absorbed energy is completely converted to thermal energy. I am simply trying to understand absolute thermal maximums from the sample from the laser exposure.
 
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Draw a diagram that shows the flow of energy from the laser to all the thermal and chemical products.
 
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Are you really referring to a pulse, or are you referring to a laser beam that is suddenly turned on and then allowed to continue irradiating the sample?
 
Chestermiller said:
Are you really referring to a pulse, or are you referring to a laser beam that is suddenly turned on and then allowed to continue irradiating the sample?
Yes, I am really referring to a pulse. The laser pulse width is ~6ns from the experiment.
 
With a 6ns pulse width, you will be dumping a ludicrous amount of peak power into the target sample. Depending on the absorbance, you may see ablation of the target. To calculate the temperature change of the target (as per the original post), you will need to factor in the latent heat due to ablation.

Overall, the advice from @Baluncore in post #2 still applies.
 
Twigg said:
With a 6ns pulse width, you will be dumping a ludicrous amount of peak power into the target sample. Depending on the absorbance, you may see ablation of the target. To calculate the temperature change of the target (as per the original post), you will need to factor in the latent heat due to ablation.

Overall, the advice from @Baluncore in post #2 still applies.
This makes sense. Could you point me in the direction to get started with this?
 
As in post #2, start by drawing a diagram that shows the flow into your sample from the laser, as well as the flow of power out of your system due to ablation and any other losses (conduction, etc.).
 

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