Question concerning the definition of pump-probe signal

[ZHuang]

Dear all,

In the paper "Exciton-exciton transitions involving strongly bound excitons: An ab initio approach, PRB, 107, 205203 (2023)" and tutorial "https://www.yambo-code.eu/wiki/index.ph ... note-pnp-1" the pump and probe simulation gives the result as "the pump&probe minus the one of generate by the pump only", namely, Delta_P(t)=P_PnP(t)-P_pump(t).

In experiment we usually monitor the signal difference of the PROBE beam with and without pump as a function of the time delay (t_delay) between the PROBE beam and the PUMP beam. That is, Delta_I(t_delay)=I_PnP(t_delay)-I_PROBE(t_delay), where I_PnP is the intensity of PROBE beam with Pump and I_PROBE is the intensity of PROBE beam without pump. For example, the setup introduced in https://pubs.acs.org/doi/10.1021/acsnano.5b06488

My question is why in the simulation the P_pump (t) was used to in the subtraction rather than P_PROBE(t).

Zhipeng Huang
Tongji University, PR China

[Davide Sangalli]

Dear Zhipeng Huang,
from the Fourier transform of

Screenshot from 2023-07-13 09-02-34.png

we obtain the frequency dependent polarization

Screenshot from 2023-07-13 09-04-42.png

and later the signal in presence of the pump

Screenshot from 2023-07-13 09-06-32.png

This procedure is used in many work in the literature and is also what is done for the post-processing of the analysis of the experimental data.
It gives you what you define as "I_PnP(omega,t_delay)" (I added the frequency dependence)

If the signal is detected in an energy range where there is absorption at equilibrium, usually the equilibrium signal is subtracted to obtain the transient signal.
What you express as "Delta_I(omega,t_delay)=I_PnP(omega,t_delay)-I_PROBE(omega)" (I probe does not depend on t_delay)
See for example this work: https://doi.org/10.1103/PhysRevMaterials.5.083803 where the above mentioned procedure is used, and later the equilibrium spectrum is removed to obtain the transient signal (figure 5 in the manuscript).

In the paper "Exciton-exciton transitions involving strongly bound excitons: An ab initio approach, PRB, 107, 205203 (2023)" instead we focus on an energy range where I_PROBE(omega)=0

Best,
D.

[ZHuang]

Dear Davide Sangalli

Thank you very much for the reply.

Zhipeng Huang
Tongji University, PR China