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Question: How exactly is the temporal dynamic range for pump-probe experiments defined, and what limits this?

My interpretation: Just by tasting the word: temporal refers to the time resolution, while dynamic range refers to the range of time resolutions we are able to obtain. However, how is this quantity defined?

I found (Ultrafast Lasers: Theory and Applications (2005), Fermann et al., page 414) that the temporal dynamic range is the ratio of the available scanning range and the timing accuracy.

So the theoretical temporal dynamic range, assuming we have an infinitely long table with a moving mirror, would be limited by the coherence length $l_c$ and the timing accuracy, where $c$ is the speed of light in air $\nu$ is the bandwidth of the laser output.

$$ l_c = \frac{c}{\Delta \nu} $$

The timing accuracy, which interpret to be the accuracy with which one can say when the probe pulse reaches the sample, will be limited by a number of factors, e.g. the step-size of the mirror's delay motor, and accuracy of when the amplified stimulated emission is coupled out of the laser cavity. Of these, I would think that the moving mirror is the largest source of error, so assuming the out-coupling from the laser cavity is known perfectly, the temporal dynamic range would then be limited by the coherence of the laser pulse and accuracy of the delay mechanism. Of course, the necessary step-size in the delay motor depends on the the pulse length; a 50 ps pulse does not really require femtosecond accuracy in the delay mechanism, as likely this will not affect the data significantly.

Is this a reasonable argument, or are there some other major contributor to inaccuracy that should be considered? Then there is the amplitude dynamic range, which I cannot find any information about.

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  • $\begingroup$ This is very long and unclear question $\endgroup$
    – anon01
    Sep 25, 2016 at 11:36

1 Answer 1

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Dynamic range is defined as maximum detectable signal / minimum detectable signal.

I am not sure what you mean by temporal dynamic range and its relation with coherence because both coherent and incoherent optical pulses are used in pump/probe studies.

I also don't understand what you mean by

Of these, I would think that the moving mirror is the largest source of error, 

As I understand your question is something like

In a pump probe experiments: what is

  1. temporal resolution
  2. temporal range

First is limited by two factors

  • duration of the pump
  • duration of the probe

The second is decided by

  • Temporal span of the actual process

For example let us say that duration of both your pump and probe is $10$ femtoseconds then your temporal resolution will be $\sqrt{2}\times10$ femtoseconds. Suppose the process last for 1 nanoseconds then the range of detection will be 1-2 nanoseconds. However if you keep on changing delay in the steps of 10 femtoseconds for 1 nanosecond it will take days to collect the data depending on your acquisition speed.

Your argument is reasonable that you don't need to change the delay with femtosecond accuracy for picosecond pulse. Also if the process is slow like 10s of nanosecond never mind the placement accuracy of mirrors in a few 10s of picoseconds.

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