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AIXscan - Measurement Technology for Terahertz Spectroscopy

AIXscan® is an integrated measurement and control solution for analysing ultra-fast signals by means of Terahertz Spectroscopy (THz measurements). Typical applications are:

  • THz analysis and imaging
  • Time-resolved femtosecond laser metrology (fs-spectroscopy)
  • Electro-optical sampling
  • Environmental and Biological Analysis
  • Pump-probe experiments with optical and mechanical delay

It supports all of the following optical methods (no mechanical delay line):

  • Asynchronous Optical Sampling (ASOPS)
  • Electronically Controlled Optical Sampling (ECOPs)
  • Optical Coherence Tomography (OCT)

Measurement and Control Technique

A common approach for time-resolved measurements with time scales in the range t <10-12s is a Pump-Probe Setup with pulsed picosecond or femtosecond laser. The ultra-short laser pulses are used to scan the desired measurement signal in a stroboscopic manner at shortest intervals. With detectors such as the THz Near Field Tip, the terahertz signal is transposed into a measurable frequency range.

Terahertz Probe
Fig.1: THz-Tip

In a Pump-Probe Setup, the laser beam is split into a pump pulse and a slightly delayed probe pulse. The pump pulse excites the sample whereas the probe pulse analyzes the response (change in reflectance and transmittance of the sample). In the course of the overall measurement the time delay between the two pulses is varied by means of a motorized delay stage. The classical approach to improve the signal-to-noise ratio (SNR) is a so-called lock-in amplifier. For every delay stage the amplifier measures the induced signal changes over a certain period in time and then calculates the mean of the results. However, this approach causes long measuring times and high sensitivity to slow signal changes (e.g. drifts) and fluctuations of the laser.

The fully integrated AIXscan system overcomes these drawbacks and enables a drastic reduction of total measurement times. AIXscan is based on the proven SATURN Transient Recorder and combines rapid data acquisition, noise reduction and delay control in one system. It leverages the powerful FastScan signal averaging technology by  AMOtronics, which replaces the lock-in amplifier. A high-precision delay control and class D amplifiers ensure an extremely accurate and reliable control of the test setup.

Advantages of the FastScan Technology

The particularity of the AIXscan system is the precise synchronization of data acquisition and control delay. The motorized delay stage is used here only for coarse adjustment. During the measurement the AIXscan system controls a fast Shaker, which periodically changes the path length of the laser at a very high frequency. By ultalising the real-time FastScan technology the measuring unit in parallel records complete transients of the signal and stores them directly in the memory of the SATURN data acquisition boards (on-board memory). This allows a drastic reduction of total measuring time and makes the system insensitive to signal drifts. The scan rate reaches up to 100 transients per second, which is significantly above the low-frequency noise of the laser. The FastScan technology of AMOtronics enables the AIXscan system to reach a signal-to-noise ratio (SNR) from 106 to 109 even for very small signals.

Schematic sketch of a pump-probe setup
Fig.2: Schematic sketch of an AIXscan-Pump-Probe setup

AIXscan Software

Another not to be underestimated advantage of the AIXscan system is the software provided. The AIXscan software is based on the versatile SATURN Studio II software. It makes it very easy to configure the hardware, to control the measurement setup and to analyse the results interactively in a convenient way. Upon request, a fully automated evaluation including report generation is also available, thus saving even more valuable time.

AIXscan menues within SATURN Studio II

Fig.3: Screenshot of the AIXscan menus within SATURN Studio II