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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)
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