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Boxcar Averagers

Boxcar averagers are attractive tools to achieve a high signal-to-noise ratio (SNR) in a minimal amount of measurement time when working with low duty-cycle signals. Such signals contain relevant information only in a fraction of each period; outside that fraction only noise is present. Capturing low duty-cycle signals with high quality and the ability for real-time feedback is crucial in many applications in optics and photonics, nanotechnology and materials science, quantum technologies, scanning probe microscopy, and sensing.

The graphic below illustrates the principle of boxcar averaging: limiting the measurement to a well-defined temporal window in each period, indicated in grey, means that all signal components outside of that window are rejected. Unlike a regular digitizer or an oscilloscope, the measurement results are immediately available in the digital domain and as analog signals with a user-defined offset and scaling factors.  Moreover, integrated PID controllers can process the results to create feedback loops and the lock-in amplifier units can perform additional demodulation on the boxcar results if an additional modulation is present.

Boxcar measurement with Zurich Instruments' boxcar averager

 

Boxcar Averager for Lock-in Amplifiers

The Zurich Instruments Boxcar Averager operates as a high-speed digitizer synchronized to a reference oscillator that is phase-locked to the periodicity of the experiment. In the case of the laser repetition rate, for example, every data sample recorded at the input can be associated with the phase of the experiment and the signal components not synchronized with the experiment are strongly suppressed. The implementation based on an external reference signal removes the trigger jitter, and the digital realization enables a dead-time-free operation.

2 Boxcar Averagers for 600 MHz Lock-in Amplifier

  • 2 periodic waveform analyzers 
  • Baseline suppression
  • Zero acquisition dead time

LabOne instrument control software

Measurements are easily set up and controlled with the LabOne® software. The graphical user interface offers a rich toolset including a periodic waveform analyzer (PWA): the PWA displays the signal with a user-controllable averaging amount to make it straightforward to operate the boxcar averager with both high and low SNR signals. With this tool, setting the boxcar windows only requires users to delimit the time interval to be measured with the cursors, as shown in the graph above.

User Benefits

  • Save time on high-quality measurements of low duty-cycle signals.
  • Choose the best-suited technique for every new experiment: boxcar averaging, lock-in detection or both.
  • Demanding schemes and methods such as double modulation, baseline suppression and feedback loop operation become straightforward to implement thanks to the LabOne toolset.

Videos

Recovering signals in optical experiments

Focus on Recovering Signals in Optical Experiments

Optimize the signal acquisition for optics and photonics measurements

Optimize the Signal Acquisition for Optics and Photonics Measurements

Publications

Fimpel, P. et al.

Boxcar detection for high-frequency modulation in stimulated Raman scattering microscopy

Appl. Phys. Lett. 112, 161101 (2018)

Schumacher, Z., Miyahara, Y., Spielhofer, A. & Grutter, P.

Measurement of surface photovoltage by atomic force microscopy under pulsed illumination

Phys. Rev. Applied 5, 044018 (2016)

Meier, St.M., Tsankov, Ts.V., Luggenhölscher, D. & Czarnetzki, U.

Measurement of plasma densities by dual frequency multichannel boxcar THz time domain spectroscopy

J. Phys. D: Appl. Phys. 50, 245202 (2017)

Sternbach, A.J. et al.

Artifact free time resolved near-field spectroscopy

Opt. Express 25, 28589-28611 (2017)

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