The common experiment for time-resolved measurements on ultra short time scales is an optical pump-probe setup. The response of the sample (e.g. change of reflectivity or transmission) to a pump pulse is probed by a second pulse variably time-delayed with respect to the pump pulse. The classic approach uses a chopper to modulate the pump induced signal and a Lock-In amplifier to measure the changes for different time delays achieved with a motorized delay stage.

The main advantage of the AIXScan® system is to use a fast scanning delay generator for the time delay and accumulating the signal with a fast A/D converter without modulating one of the laser beams. This technique, first introduced in the 80`s, allows to average thousands of scans within minutes.  In the 90`s the ultra fast optics group of H. Kurz at the Technical University of Aachen (or AIX-la-Chapelle) developed a specialized VME-Bus based computer hardware, which allows Megasample A/D conversion rate and online data processing. Using scan frequencies up to 100 Hz, well above low frequency noise of the laser, a signal-to-noise ratio of 106 to 109 is achieved within minutes.

AMO GmbH developed a capable system based on digital signal-processors (DSP) integrated in a PCI plugin card for measurement control, data acquisition and processing, which offers the ability to integrate even complex filter-algorithms.

AIXScan® makes this technique available for everybody working in the field of ultra fast spectroscopy. The system features up-to-date PC-based hardware and software.

Features of the AIXScan® System:

  • short measurement times compared to Lock-In based detection
  • typical SNR of 106 to 109 reached within minutes e.g. for semiconductor pump-probe measurements
  • sampling rates up to 50 MHz
  • D/A converter with max. amplitude of +/- 10V and frequencies up to 100 MHz
  • additional amplifier for shaker driving, also available by AMO GmbH
  • online optimization of optical alignment
  • user friendly Labview program running under Windows 2000 for full control of the measurement and the stepper movement
  • integration of every stepper or dc-based motor system possible
  • fully automatic calibration of the time axis to account for the exact shaker motion
  • possibility of subtracting a background signal (e.g. a modulation due to stray light)
  • standard file management for loading and saving data files

Typical applications for the AIXScan® System

  • optical pump–probe setup with femtosecond laser pulses for analyzing sub–ps phenomena e.g. phonon relaxation in semiconductors, liquids and other material systems
  • pump-probe, four-wave mixing and other time resolved optical measurements
  • applications with high repetition rate fs laser sources (> 1GHz )
  • real-time auto-correlation measurements
  • quick detection of coherently generated THz pulses for e.g. material characterization
    • analysis of doping in semiconductors
    • imaging applications in tomography or transillumination
    • analysis of biological samples (e.g. DNA)
    • sensitive analysis of humidity (e.g. in human dermis, in drying processes)
  • general usage of the AIXScan® measurement card for fast data acquisition (up to 50 MHz) and preprocessing (e.g. averaging)

More information on this work:

  • Femtosecond Relaxation Dynamics of Large Molecules
    M. Rosker, T.W. Wise, and C.L. Tang, Physical Review Letters, 57, 321 (1986)
  • Subpicosecond time-resolved coherent-phonon oscillations in GaAs
    G.C. Cho, W. Kütt, and H. Kurz, Physical Review Letters 65, 764 (1990)
  • Femtosecond Tisapphire ring laser with a 2-GHz repetition rate and its application in time-resolved spectroscopy
    A. Bartels, T. Dekorsy, and H. Kurz, Optics Letters 24, 996 (1999)

[Martin Brucherseifer] [About me] [Resume] [SEM / FIB] [Scanning Probe Microscopy] [THz Spectroscopy] [AIXScan] [Publications] [Links] [Disclaimer]