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I was in class today, and we had a presentation by a student on how tunable lasers are used in fiber optics and change the wavelength. He also explained that by "pump probe measurements" a "sample gets excited and can be measured over time".

Can anyone explain what this means? What is a "sample"? How are "pump probe measurements" useful when dealing with tunable lasers?

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  • \$\begingroup\$ You should rather ask this question at physics.stackexchange.com . \$\endgroup\$ – starblue Sep 25 '12 at 20:16
  • \$\begingroup\$ @starblue That is a good point. I asked a fiber optics question there last time, and no one answered. Where does the topic of fiber optics belong? \$\endgroup\$ – Ci3 Sep 25 '12 at 20:28
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From the Encyclopedia of Laser Physics and Technology:

Pump–probe measurements can be used to obtain information on ultrafast phenomena. The general principle is the following. A sample (e.g. a SESAM) is hit by some pump pulse, which generates some kind of excitation (or other modification) in the sample. After an adjustable time delay (controlled with an optical delay line), a probe pulse hits the sample, and its transmission or reflection is measured. By monitoring the probe signal as a function of the time delay, it is possible to obtain information on the decay of the generated excitation, or on other processes initiated by the pump pulses.

From the Wikipedia article on Time-resolved spectroscopy:

Transient-absorption spectroscopy is an extension of absorption spectroscopy. Here, the absorbance at a particular wavelength or range of wavelengths of a sample is measured as a function of time after excitation by a flash of light. In a typical experiment, both the light for excitation ('pump') and the light for measuring the absorbance ('probe') are generated by a pulsed laser.

The "sample" is anything that you want to get the spectrogram of.

This article mentions photochemistry as one possible application. It also notes that:

in some applications such as spectroscopy and pump-probe experiments, the laser wavelength must be tuned continuously during the experiment or test.

So, it's not that pump-probe measurements are useful when dealing with tunable lasers, its that tunable lasers are useful when dealing with pump-probe measurements.

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