Temperature change in HEAT from an optical signal modulated in time


#1

Hello,
I would like to simulate the transient temperature change in a sample, when the incident optical signal is modulated in time. This is the an application of photo-acoustic technique, where the absorbed power generates heat that strongly depends on the modulation frequency. In our experiments we have to measure signals with modulation frequencies from 25Hz to 315Hz. Do I need interconnect to simulate this and what are the application examples that would connect FDTD, modulate it in time and transport it in heat?


#2

Hi @emilija.petronijevic, the general workflow of such a simulation would ideally be that you would perform a steady state simulation in FDTD for a CW optical source. You can then import the power absorption data into the HEAT solver in DEVICE for a transient simulation. The HEAT solver in DEVICE includes a global shutter that can then be used to turn the optical absorption input ON and OFF to create a pulse. You can record the response of the system temperature to this pulse and get the thermal response of the system this way.

A relevant example would be the microbolometer example in KB (https://kb.lumerical.com/en/index.html?metamaterials_microbolometer.html). At the bottom of this example you will find a plot of the thermal response of the device under investigation calculated using this approach.

Unfortunately there is currently no option to modulate the power absorption input at certain frequencies. However, you can use the above mentioned method to calculate the step response of the thermal system and get the impulse response of the system from that. Once you have the impulse response, you will be able to get the response of the system at any frequencies. We do not have any examples on the knowledge base currently that does something like this for a thermal system. However a similar approach was used in his example (https://kb.lumerical.com/en/index.html?pic_photodetectors_vertical_photodetector.html) where the impulse response of a photodetector was calculated using this method.