About the Field direction in Pump Probe simulation

Questions and doubts about features of non linear optic in Yambo (yamb_nl)

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About the Field direction in Pump Probe simulation

Post by ZHuang » Fri Jul 14, 2023 4:56 am

Dear All,

I am following the pump probe simulation procedure introduced in https://www.yambo-code.eu/wiki/index.php/Pump_and_Probe.
The version of yambo is 5.1.0 Revision 21422 Hash fde6e2a07.
I used all setting suggested by the tutorial except that the version of Yambo 5.1.0 was used (the tutorial mentioned that [This tutorial works only with Yambo version > 5.1.2].

I am confused about the relationship between the direction of Field and the epsilon.
In the probe only calculation, the direction of probe field is defined as

Code: Select all

% Field1_Dir
   0.000000 | 1.000000 | 0.000000 |        # [RT Field1] Versor
I found that the plot of column 1 (E[eV]) and column 2 (Im/eps_d1) in the file o-PROBE.YPP-eps_along_E matched well with that in the tutorial. That is, the polarization long y direction determine dielectric constant along X direction. Is it right?

Question 1:
So my first question is how to define the direction of Field according to the Epslion in the direction of interesting? For example, which direction of Field should I define if I want to know the epsilon along Z direction?

When I go further to the PUMP_AND_PROBE calculation with Field direction defined as

Code: Select all

Field1_NFreqs= 1                 # [RT Field1] Frequency
Field1_Int=  1.00       kWLm2 # [RT Field1] Intensity
Field1_Width= 0.000000     fs    # [RT Field1] Width
Field1_kind= "DELTA"           # [RT Field1] Kind(SIN|COS|RES|ANTIRES|GAUSS|DELTA|QSSIN)
Field1_pol= "linear"             # [RT Field1] Pol(linear|circular)
% Field1_Dir
 1.000000 | 0.000000 | 0.000000 |        # [RT Field1] Versor
Field1_Tstart= 90.0000    fs    # [RT Field1] Initial Time
% Field2_Freq
  5.42 | 5.42 |         eV    # [RT Field2] Frequency
Field2_NFreqs= 1                 # [RT Field2] Frequency
Field2_Int=  1000.00       kWLm2 # [RT Field2] Intensity
Field2_Width= 10.00000     fs    # [RT Field2] Width
Field2_kind= "QSSIN"             # [RT Field2] Kind(SIN|COS|RES|ANTIRES|GAUSS|DELTA|QSSIN)
Field2_pol= "linear"             # [RT Field2] Pol(linear|circular)
% Field2_Dir
 0.000000 | 1.000000 | 0.000000 |        # [RT Field2] Versor
Field2_Tstart= 0.010000    fs    # [RT Field2] Initial Time

I can also reproduce the pump and probe spectrum by plotting col 1 (E [eV]) and col 2 (Im/eps_d1 ) in o-PUMP_AND_PROBE.YPP-eps_along_E.
In brief, the Field of PROBE beam is in X direction and that of the PUMP beam in Y direction, and we got pump and probe spectrum in X direction.

Question 2.
In the probe only calculation, it seems that the direction of epsilon we analyze is different from the direction of probe beam. While in the pump and probe calculation the direction of spectrum (epsilon) we analysis is the same as the direction of PROBE beam.
so the same question is "how to define the direction of PROBE beam and PUMP beam according to the direction of interesting in pump and probe calculation"

Thank you very much for your help!
Zhipeng Huang
Tongji University

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Davide Sangalli
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Re: About the Field direction in Pump Probe simulation

Post by Davide Sangalli » Fri Jul 14, 2023 2:16 pm

Dear Zhipeng Huang,

1) the direction of the probe field determines one of the two indexes in the dielectric function tensor.
Say that your probe is E_x, along direction "x".

Then, after real time you will know the polarization induced along three direction "x", "y",and "z"

Code: Select all

P_beta(w) = chi_{beta,alpha}(w) E_alpha(w)
you will be able to compute
chi_{xx}(w), chi_{yx}(w), chi_{zx}(w)

2) when you do pump and probe, the polarization of the pump will determine which states are excited, but it is not directly related to the probe measurement.
Suppose you have a pump EP_gamma, and then again the probe E_x. Accordingly:

Code: Select all

P_beta(w) = chi_{beta,alpha}[EP_gamma](w,tau)  E_alpha(w)
where tau is the time delay between the pump and the probe.
you will be able to compute
chi_{xx}[EP_gamma](w,tau), chi_{yx}[EP_gamma](w,tau), chi_{zx}[EP_gamma](w,tau)

You can explore how the results are affected by the direction of the pump (gamma), the direction of the probe (alpha, in the example alpha=x) and of the polarization which you want to detect (beta). Usually we look into beta=alpha, but in some cases it might be interesting to measure a different direction as well.

Davide Sangalli, PhD
CNR-ISM, Division of Ultrafast Processes in Materials (FLASHit) and MaX Centre

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Joined: Sat Jul 08, 2023 3:32 pm

Re: About the Field direction in Pump Probe simulation

Post by ZHuang » Fri Jul 14, 2023 2:58 pm

Dear Dr. Sangalli

The reply is very nice! Thank you very much !

Zhipeng Huang

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