The use of lock-in amplifiers in combination with optical choppers is one of the most common low frequency lock-in amplifier applications. In order to make this a bit more interesting, James shows in the following video how to easily set up an experiment that makes use of 2 different choppers simultaneously. This helps to save valuable real estate in the lab and reduce the complexity of the setup.

Requirements

• Single chopper experiments modulating the light on a single detector require one MFLI 500 kHz
• For dual chopper experiments using two independent detectors and different frequencies, one MFLI 500 kHz plus the MF-MD Multi Demodulator option is needed

Tips and Tricks

• Adjust the input ranges
• Sometimes it's handy to use the Auxiliary Inputs on the front panel as external reference input
• Auto-zero the phase
• Use the Plotter tool to display the chopper frequency, as tracked by the internal PLL, over time - the Math sub-tab offer plenty of statistical function for further signal analysis
• By adjusting the Harmonic field you can adjust the demodulation frequency to higher harmonics but also sub-multiples of the chopper reference frequency; this can be useful when using the same blade at multiple slot pitches
• Use the Sinc filter to increase temporal resolution while keeping SNR high, when demodulation bandwidth gets into the same range as demodulation frequency
• Use the FFT Spectrum Analyzer to determine SNR and see other components in the spectrum
• For analog outputs to the Auxiliary Output adjust the Offsets, the scaling factor and limits as needed