Photon correlation spectroscopy serves as a fundamental technique for probing the microscopic motion of particles within fluids and gels. The method relies on detecting fluctuations in the intensity of light scattered by particles, allowing researchers to infer diffusion coefficients and other dynamic properties. However, the raw data generated by modern detectors often consists of long sequences of photon arrival times, known as time-of-arrival records. Processing these extensive datasets requires sophisticated algorithms to convert raw event streams into meaningful correlation and structure functions, a task that demands substantial computational power.

In the previous iteration of the software, the entire segmentation process was executed within the LabVIEW environment. While this approach was suitable for shorter acquisition windows, it became increasingly inefficient as data lengths extended into minutes. The computational load associated with manipulating large arrays of photon events in a single environment led to prohibitively long processing times. In some instances, the software could not complete the analysis of the entire dataset, forcing researchers to truncate their data or rely on less precise approximations.

To overcome these limitations, the developers introduced a hybrid LabVIEW and MATLAB processing scheme in the new release. LabVIEW continues to manage the user interface, data acquisition, and the final stages of correlation analysis. However, the computationally intensive task of segmenting the photon event sequence has been offloaded to MATLAB routines. This strategic division of labor leverages the strengths of both platforms, allowing the software to handle significantly longer records without exceeding the memory or processing capabilities of standard computing systems.

The second major modification in version V2.1 involves a streamlined method for calculating the structure function. The structure function provides a robust alternative to the standard correlation function, particularly useful in regimes where signal-to-noise ratios are challenging. In the original implementation, this calculation required the parallel evaluation of second-order count moments for both detection channels. This process involved storing and manipulating large intermediate datasets, which further increased the computational burden and the risk of memory overflow during long analyses.

The updated software eliminates the need for explicit calculation of these second-order moments. Instead, it derives the necessary zero-lag information directly from the initial region of the normalized correlation function. The developers employ a second-order polynomial fit to the first several points of the correlation curve to estimate the correlation contrast, also known as the coherence factor. By extrapolating this polynomial fit to zero lag, the software obtains a precise estimate of the initial correlation value without requiring separate moment calculations.

This mathematical refinement simplifies the algorithm significantly. The structure function is now evaluated using a formulation that depends only on the measured mean photon counts and the estimated correlation contrast. This approach reduces the amount of intermediate data that must be stored and processed during the analysis. Consequently, the software requires fewer computational resources and operates more smoothly, even when dealing with the most demanding experimental datasets. The simplification also makes the software more intuitive for users, as the configuration options have been reduced to streamline the workflow.

The validation of the original software version was performed using data acquired from model colloidal nanoparticles embedded in polymer matrices. These systems provide a well-characterized benchmark for testing the accuracy of photon counting algorithms. The new version maintains this rigorous standard, ensuring that the computational shortcuts introduced do not compromise the physical accuracy of the results. The ability to process longer records without loss of precision is a substantial improvement for experimentalists studying slow dynamics or low-concentration samples.

The release of this updated toolbox represents a meaningful step forward in the accessibility of advanced optical analysis techniques. By reducing the technical barriers associated with processing large photon datasets, the software encourages broader adoption of photon correlation spectroscopy in various scientific fields. Researchers working with soft matter, biological fluids, and complex fluids can now utilize this tool to extract high-quality dynamic information from their experiments with greater confidence and efficiency.

The software is available under the GNU General Public License, ensuring that it remains open and accessible to the global scientific community. The developers have provided comprehensive documentation and a user manual to guide researchers through the installation and operation of the updated toolbox. This commitment to open science facilitates reproducibility and allows for further development by other groups in the field. The integration of MATLAB and LabVIEW sets a precedent for hybrid software solutions in experimental physics, demonstrating how combining different programming environments can yield superior performance for specialized scientific applications.

Subject of Research: Software optimization for photon correlation spectroscopy data analysis

Article Title: V2.1 – PhotonSTR-18: A LabVIEW toolbox for photon correlation spectroscopy

Article References: García-Cadena, C. A., Aguilar-Uribe, A. D. J., & Rojas-Ochoa, L. F. (2026). V2.1 – PhotonSTR-18: A LabVIEW toolbox for photon correlation spectroscopy. SoftwareX, 36, Article 103071. https://doi.org/10.1016/j.softx.2026.103071

Image Credits: AI Generated

DOI: 10.1016/j.softx.2026.103071

Keywords: Photon Correlation Spectroscopy, LabVIEW, MATLAB, Soft Matter Physics, Computational Science, Optical Scattering, Data Analysis, Open Source Software, Colloidal Dynamics, Signal Processing, PhotonSTR-18, toolbox