Modulated 3D Cross-Correlation Light Scattering

 
 

One drawback of the 3D cross-correlation technique is that one photon detector measures the scattered light intensity at the desired scattering vector, but also receives a contribution at a second undesired scattering vector given by the relative geometry to the second illumination beam operating at the same wavelength. A four-fold reduction in the cross-correlation intercept arises from cross-talk between the two simultaneous scattering experiments executed in this way.

The correlation intercept strongly influences measurement accuracy and precision due to its pivotal role in accurately fitting models to the measured data. For strongly scattering samples where only a small component of the detected light is singly-scattered, the signal-to-noise ratio of the measurement becomes unacceptably low as the magnitude of the cross-correlation intercept falls into the noise of the baseline fluctuations.

 

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Image presents LS Spectrometer which is an advanced instrument for DLS and SLS measurements. It enables measurement of hydrodynamic radius, radius of gyration, 2nd viral coefficient, molecular weight, form factor and structure factor.

3D LS Spectrometer

 

Image depicts NanoLab 3D which is suitable for DLS measurement of highly concentrated turbid samples

NanoLab 3D

 
 

Schematical representation of the modulated 3D-cross correlation set-upSchematical representation of the modulated 3D cross-correlation set-up.

 
 

In order to circumvent this limitation, we have developed a new measurement technique in which the two scattering experiments are temporally separated by modulating the incident laser beams and gating the detector outputs at frequencies exceeding the timescale of the system dynamics. This robust modulation scheme eliminates cross-talk between the two beam-detector pairs and leads to a four-fold improvement in the cross-correlation intercept, while fully suppressing the negative effects of multiple scattering. 

 
 
 

Measured correlation functions demonstrating the improved intercept by using the modulated 3D-cross correlation set-up

Measured correlation functions demonstrating the improved

intercept by using the modulated 3D-Cross correlation set-up.

 
 
 

The modulated cross-correlation technology is implemented in the NanoLab 3D and available as an upgrade for the 3D LS Spectrometer. It has been further improved from its original design and can now deliver even better results than previously possible.


Learn more about this useful technique in our publication in the American Institute of Physics' well-regarded Review of Scientific Instruments. 

 



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