I am currently working on photothermal conversion efficiency measurements and I’m a bit confused about which laser parameter to use in the efficiency equation. Specifically:

• In many publications, the term “I” is described as the laser intensity (power density) in W/cm².
• However, some equations appear to use the total laser power (in W) instead of power density.

For example, suppose I have:

• A continuous-wave NIR laser with an output power of 1 W
• An irradiated spot area of 0.5 cm²

Should I enter “I = 2 W/cm²” (i.e., 1 W ÷ 0.5 cm²) into the photothermal efficiency formula, or should I use “I = 1 W” (the total power) and let any area terms cancel out when calculating η?

How do you determine whether to plug in the power density (e.g., 2 W/cm²) or the total laser power (1 W) in the efficiency equation?

Any references or examples from your experience would be greatly appreciated.

Thank you!