myRIO based pump-probe measurements

[fuaran]

Pump-probe spectroscopy prepares a sample/fluorophore in a certain state with one color and then probes this state with a second. Sometimes the aim of probing is to actually deplete the prepared state, which is called pump-dump spectroscopy. As far as timing is concerned, these modes are equal.

The usual approach is to use pulsed lasers for both preparation and probing. By delaying the pulses relative to each other, the time-dependent signal carries information about the sample, e.g. the lifetime of some prepared state.

These pulsed sources are limited in their repetition rate and thereby in the accessible lifetime range. With 80 MHz repetition rate, any process slower than 12 ns cannot be resolved. For such processes the pulsed lasers are "quasi-cw" as no significant change in the sample occurred during a perioid.

If slower pulsed lasers not an option, the pulse trains from the available sources have to be shaped. Shaping is not only a way to circumvent a weakness. Being able to freely choose single laser and combined illumination times is an advantage.

Measurements in the microsecond regime require timing accuracy of less then 100 ns in order to be reliable. Fast enough rise-times for those measurements are provided by acousto-optical modulators, and FPGAs run easily even at 100 MHz.

In the pump-probe software, both the "classical" delayed pulses mode and a shaping mode are available.

The complete hardware list, the hardware and software description and the project itself is attatched.