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As the following figure illustrated,the pump-probe processes contain mainly two steps:

  1. Pump pulse drives the sample out of equilibrium (red line);
  2. Time evolution measured by subsequent probe pulses;

I have some questions for this pump-probe process:

  1. How this pump-probe procedure works,especially the second step? What's the information one can get ?

  2. What's this meaning for time resolution ~ 10fs ?Be relative to the time delay ?

enter image description here

Jack
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Pump-probe spectroscopy is a topical issue in spectroscopy research at the moment: if you Google "Pump-probe spectroscopy" then you will find a description of many research groups and their work.

The purpose of the second beam and the information it can retrieve is very varied and broad. The basic principle is:

  1. The pump beam drives the sample into an excited state;
  2. The excitation changes the samples' optical properties;
  3. The optical properties in question evolve with time as the sample relaxes back to its ground state;
  4. The probe pulse of a given delay measures the optical property in question;
  5. By repeating the process whilst varying the delay, one can measure how the optical properties evolve with time throughout the relaxation.

The evolution with time has many applications: we might want to research the dynamics of a known substance, or we might use the procedure to seek known evolutions with time and thus identify the sample's makeup.

So, for example, one might set up an experiment where the probe beam measures the sample's transmittance. Or, in an alternative kind of spectrometer, the probe beam might be one arm of an interferometer, and we thus measure the phase delay and its evolution with time.

Selene Routley
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  • The whole point of pump-probe is to study the dynamics of materials follow by photo-excitation.

  • The probe, is a way to take snapshots of the sample (mostly by measuring transmittance or reflectance).

  • However, this dynamics is very fast (normally picosecond range). You cannot just take a lot of snapshots of the sample in a single run.

  • Instead, the excitation is repeated and the snapshots are taken one at the time, but with different delay.

  • The delay is achieved by a mechanical stage. To crate 1ps delay, the stage needs to move about 0.15mm, which is well within the resolution of a brashless motor stage. For 1fs the stage needs ti move 0.15um, which is well within the resolution of a stepper motor stage. So the delay stage is not the limiting factor of your resolution.

  • The 10fs resolution limit come from the duration of the laser pulse. 10fs is an interesting value, probably a sub-100fs laser spectrally stretched through a argon-filled hollow fiber and then compressed by a set of chirp mirrors.

  • It's a terrible idea to use the same lens for pump and probe beams.

7E10FC9A
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