Pump-Probe Spectroscopy

Related products: UHF-BOX, UHFLI, HF2LI, MFLI

Pump–probe measurements are used to measure ultrafast phenomena using short laser pulses. As the pump pulse impinges on the sample, various physical phenomena can be induced, for instance an electronic excitation. After an adjustable time delay, often controlled with an optical delay line, a probe pulse then hits the sample, and its transmission and/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 dynamics of the generated excitation.

A key aspect of these measurements is the fact that the time resolution is governed by the duration of the laser pulses not the bandwidth of the photodetectors or the signal recording electronics. Numerous techniques investigating ultrafast phenomena are based on the pump-probe scheme, such as THz and Raman spectroscopy.

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Measurement Strategies

The pulse repetition rates of the lasers are typically between a few kHz to hundreds of MHz. As the signal to noise ratio of the individual pulses is often very small, sensitive detection electronics and heavy averaging is needed. Two of the most common approaches are:

  • Use fast photodetectors in combination with Boxcar averaging. This allows the signal to be recorded over a small duty cycle and therefore excludes the vast amounts of data recording time where only noise is present. This method offers the highest SNR but is also the most demanding for the electronics.
  • Another strategy is to adjust the bandwidth of the photodetector such, that the resulting signal covers the entire period and is close to a sinusoidal. This technique allows the use of a lock-in amplifier for signal detection, which is easy to set up and provides sufficient SNR as all non-synchronous noise components are efficiently rejected.

Your benefits measuring with Zurich Instruments

  • With Zurich Instruments you can pursue both measurement strategies. In fact, on the UHFLI both strategies can run simultaneously and can be directly compared. For low repetition rate and experiments on a lower budget, the HF2LI or MFLI are attractive alternatives for the second approach.
  • The UHF-BOX is the only synchronous boxcar averager and consequently rejects all noise sources not in synchronization with your lasers.
  • The UHF-BOX Boxcar acquires data without dead-time thus minimizing the total measurement time.
  • With the Periodic Waveform Analyzer, a highly averaged view of your basic signal allows you to easily define the boxcar windows.
  • If your setup allows to “blank” every second pump-pulse, our “background subtraction feature” allows you to take measurements independent of the background noise and DC shifts of the signal.

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