Heating by Laser: DC Temperature & Modulation Frequency

[bushjun]

A laser beam whose intensity is modulated (at frequency, f) is falling on a black absorber. For the surface temperature, there will be two components: (1) modulated temperature or photothermal wave and (2) a static dc temperature component.

The photothermal signal properties are well known. But, can some one clarify why the static temperature at steady state is a function of laser modulation frequency ?
To make it clear, at steady state, the static temperature is found to be increasing with frequency of laser modulation. The material is carbon black.

For the laser, energy is independent of modulation frequency. Why the dc temperature
goes up with frequency ?

 

[BigJDubs]

The answer is related to how quickly the material can absorb and dissipate the energy from the laser. Generally speaking, when the laser is modulated at a higher frequency, the material has less time to absorb and dissipate the energy, resulting in a higher static temperature. This is because the time available for the material to absorb and dissipate the energy is reduced as the frequency increases. The rate of energy absorption and dissipation will therefore be lower, leading to a higher static temperature.