Invited talk by G. Volpe at RIAO/Optilas 2019, Cancun, Mexico, 23 Sep 2019

Deep Learning Applications in Digital Video Microscopy and Optical Micromanipulation
Saga Helgadottir, Aykut Argun, Giovanni Volpe
Invited talk at RIAO/Optilas 2019, Cancun, Mexico, 23-27 September 2019

Since its introduction in the mid 90s, digital video microscopy has become a staple for the analysis of data in optical trapping and optical manipulation experiments [1]. Current methods are able to predict the location of the center of a particle in ideal condition with high accuracy. However, these methods fail as the signal-to-noise ratio (SNR) of the images decreases or if there are non-uniform distortions present in the images. Both these conditions are commonly encountered in experiments. In addition, all these methods require considerable user input in terms of analysis parameters, which introduces user bias. In order to automatize the tracking process algorithms using deep learning have been successfully introduced but have not proved to be usable for practical applications.

Here, we provide a fully automated deep learning tracking algorithm with sub-pixel precision in localizing single particle and multiple particles’ positions from image data [2]. We have developed a convolutional neural network that is pre-trained on simulated single particle images in varying conditions of, for example, particle intensity, image contrast and SNR.

We test the pre-trained network on an optically trapped particle both in ideal condition and challenged condition with low SNR and non-uniform distortions [3]. This pre-trained network accurately predicts the location the trapped particle and a comparison of detected trajectories, the distribution of the particle position and the power spectral density of the particle trajectory clearly shows that our algorithm outperforms tracking by radial symmetry [4]. Our algorithm is also able to track non-ideal images with multiple Brownian particles as well as swimming bacteria that are problematic for traditional methods.

In conclusion, our algorithm outperforms current methods in precision and speed of tracking non-ideal images, while eliminating the need for user supervision and therefore the introduction of user biases. 


[1] John C Crocker, David G Grier, Journal of Colloid and Interface Science 179, 298–310 (1996).

[2] Saga Helgadottir, Aykut Argun, Giovanni Volpe, Optica 6, 506–513 (2019).

[3] Philip H Jones, Onofrio M Maragò, Giovanni Volpe, Optical tweezers: Principles and applications. Cambridge University Press, 2015.

[4] Raghuveer Parthasarathy. Nature Methods 9724 (2012).

Saga Helgadottir interviewed by Curie, a magazine issued by the Swedish Research Council

Saga Helgadottir discussed her research with Curie, a magazine issued by the Swedish Research Council. The article gives examples of how AI is used in many research disciplines. Read the article on Curie’s webpage here.

Seminar by G. Volpe at the Department of Chemistry, University of Gothenburg, 19 Sep 2019

Soft Matter Meets Deep Learning
Giovanni Volpe
Department of Chemistry, University of Gothenburg, Sweden
19 September 2019

After a brief overview of artificial intelligence, machine learning and deep learning, I will present a series of recent works in which we have employed deep learning for applications in photonics and active matter. In particular, I will explain how we employed deep learning to enhance digital video microscopy [1], to estimate the properties of anomalous diffusion [2], and to improve the calculation of optical forces. Finally, I will provide an outlook for the application of deep learning in photonics and active matter.


[1] S. Helgadottir, A. Argun and G. Volpe, Digital video microscopy enhanced by deep learning. Optica 6(4), 506—513 (2019)
doi: 10.1364/OPTICA.6.000506

[2] S. Bo, F Schmidt, R Eichborn and G. Volpe, Measurement of Anomalous Diffusion Using Recurrent Neural Networks. arXiv: 1905.02038

Seminar on controlled generation of high power optical vortex arrays by Harshith Bachimanchi from IISER Pune, Faraday, 18 September 2019

Harshith Bachimanchi. (Photo by A. Argun)
Controlled generation of high power optical vortex arrays, and their frequency-doubling characteristics
Seminar by Harshith Bachimanchi from the Indian Institute of Science Education and Research, Pune (IISER Pune).

Optical vortices, beams carrying orbital angular momentum (OAM) per photon are of supreme interest in recent times for their wide variety of applications in quantum information, micro-manipulation, and material lithography [1, 2, 3]. Due to a helical phase variation in propagation, and an undefined phase at the centre, these beams have a phase singularity in their wavefront, resulting in the doughnut-shaped intensity distribution. Though the vortex beams have been widely explored in the past, the recent advancements on multiple particle trapping, single-shot material lithography, and multiplexing in quantum information [4] demand an array of optical vortices in a simple experimental scheme.

While the majority of the existing mode converters transform the Gaussian beam into a single vortex beam, the intrinsic advantage of the dynamic phase modulation through holographic technique allow the spatial light modulators (SLMs) to generate vortex arrays directly from a Gaussian beam. However, the low damage threshold of SLMs restricts their usage for high power vortex array applications.

Here, we elaborate a simple experimental scheme to generate high power, ultrafast, higher order optical vortex arrays. Simply by using a dielectric Microlens array (MLA) and a plano-convex lens we generate an array of beams carrying the spatial property of the input beam. Though we’ve verified the technique for the case of optical vortices, it holds true for a useful subset of structured optical beams. Considering the MLA as a 2D sinusoidal phase grating, we have numerically calculated the intensity pattern of the array beams in close agreement with the experimental results. We have also theoretically derived the parameters controlling the intensity pattern, size and the pitch of array and verified experimentally. The single-pass frequency doubling of the vortex array at 1064 nm in a 1.2 mm BiBO crystal produced green vortex arrays of orders as high as lsh = 12, twice the order of the pump array beam, with a conversion efficiency as high as ∼3.65% [5].


  1. Grier, D. G. A revolution in optical manipulation. Nature 424, 810 (2003)
  2. Mair, A., Vaziri, A., Weihs, G. & Zeilinger, A. Entanglement of the orbital angular momentum states of photons. Nature 412, 313 (2001).
  3. Scott, T. F., Kowalski, B. A., Sullivan, A. C., Bowman, C. N. & McLeod, R. R. Two-color single-photon photoinitiation and photoinhibition for subdiffraction photo-lithography. Science 324, 913–917 (2009).
  4. Omatsu, T. et al. Metal microneedle fabrication using twisted light with spin. Opt. Express 18, 17967–17973 (2010).
  5. Harshith, B.S., Samanta, G.K. Controlled generation of array beams of higher order orbital angular momentum and study of their frequency-doubling characteristics. Sci Rep 9, 10916 (2019).

Place: Faraday room, Fysik Origo, Fysik
Time: 18 September, 2019, 15:00

CECAM Workshop “Active Matter and Artificial Intelligence Location”, Lausanne, Switzerland 30 September – 2 October 2019

Active Matter and Artificial Intelligence
Location : CECAM-HQ-EPFL, Lausanne, Switzerland
September 30, 2019 – October 2, 2019

Frank Cichos (Universität Leipzig, Germany)
Klaus Kroy (Universität Leipzig, Germany)
Fernando Peruani (Université Nice Sophia Antipolis, France)
Giovanni Volpe (University of Gothenburg, Sweden)


Biological active matter is composed of self-propelling agents, such as molecular motors, cells, bacteria and animals [1,2], which can perform tasks and feature emergent collective behaviors thanks to their capability of sensing their environment, processing this information and exploiting it through feedback cycles [3]. These processes are intrinsically noisy [4] both at the microscale (e.g. thermal noise [5]) and at the macroscale (e.g. turbulence [6]). Therefore, through millions of years, biological systems have evolved powerful strategies to accomplish specific tasks and thrive in their environment – strategies that are encoded in their shape, biophysical properties, and signal processing networks [13].

Artificial active matter is now being explored as a powerful means to address the big challenges that our society is facing [7]: from new strategies for targeted drug delivery, to the decontamination of polluted soils, to the extraction of energy from naturally occurring out-of-equilibrium conditions. In this context, biological active matter provides an ideal source of tested ideas and approaches [8,9], which we are now trying to exploit to develop artificial systems [10,11].

However, in biological systems, there is only a limited possibility to reduce complexity and introduce controllable perturbations. Therefore, the development of computational models and of proof-of-principle experiments provides an ideal test bench to explore the origin of complexity in biological systems and to harness it for the development of new applications. For example, tuning of sensorial delays yield different behaviors in gradient fields relevant for cellular systems [12], and, inspired by neuronal networks, relevant past experience is harnessed to predict the evolution of complex systems.

In this process, we have been led to the application of machine learning to active matter. Machine learning is an abstraction of the adaption processes found in biological active matter and researchers have recently started to explore these algorithms in active matter in some pioneering works. For example, reinforcement learning [14], which reflects a type of learning based on rewards, has been used to steer the motion of microscopic particles [15,16], to understand how birds can exploit turbulent thermal air flows to soar [6], to control the motion of artificial microswimmers in complex flow patterns [17] as well as in collective field taxis [18].

We are now at a critical crossroad in the development of active matter research where biological and artificial active matter are meeting with machine learning. The specific aim of this workshop is to bring together researchers from the fields of physics, biology, mathematics and machine learning to lay the groundwork of a scientific network to address the pressing questions:

1. What can machine learning do for biological active matter? Can we gain new insight into how powerful strategies have evolved? Can we understand the role of information processing, feedback cycles and sensorial delay in these strategies?

2. What can machine learning do for artificial active matter? Can we learn new approaches towards high-impact applications? For example, how can signaling and feedback be introduced into artificial active matter?

3. What insights can active matter provide for machine learning? Can we get some insight from the natural strategies optimized by evolution?


[1] Ramaswamy, S., The mechanics and statistics of active matter. Annu. Rev. Condens. Matter Phys. 1, 323–345 (2010).

[2] Marchetti, M. C. et al., Hydrodynamics of soft active matter. Rev. Mod. Phys. 85, 1143–1189 (2013).

[3] Katz, Y., Tunstrøm, K., Ioannou, C. C., Huepe, C., Couzin, I. D., Inferring the structure and dynamics of interactions in schooling fish. Proc. Natl. Acad. Sci. USA 108, 18720–18725 (2011).

[4] Yates, C. A. et al., Inherent noise can facilitate coherence in collective swarm motion. Proc. Natl. Acad. Sci. USA 106, 5464–5469 (2009).

[5] Kromer, J. A., Märcker, S., Lange, S., Baier, C., Friedrich, B. M., Decision making improves sperm chemotaxis in the presence of noise. PLoS Comput. Biol. 14, e1006109–15 (2018).

[6] Reddy, G., Celani, A., Sejnowski, T. J., Vergassola, M., Learning to soar in turbulent environments. Proc. Natl. Acad. Sci. USA 113, E4877–84 (2016).

[7] Bechinger, C. et al., Active particles in complex and crowded environments. Rev. Mod. Phys. 88, 045006 (2016).

[8] Pearce, D. J. G., Miller, A. M., Rowlands, G., Turner, M. S., Role of projection in the control of bird flocks. Proc. Natl. Acad. Sci. USA 111, 10422–10426 (2014).

[9] Bierbach, D. et al., Insights into the social behavior of surface and cave-dwelling fish (Poecilia mexicana) in light and darkness through the use of a biomimetic robot. Front. Robot. AI 5, 15 (2018).

[10] Buttinoni, I. et al., Dynamical clustering and phase separation in suspensions of self-propelled colloidal particles (2017).

[11] Qian, B., Montiel, D., Bregulla, A., Cichos, F., Yang, H., Harnessing thermal fluctuations for purposeful activities: the manipulation of single micro-swimmers by adaptive photon nudging. Chem. Sci. 4, 1420–1429 (2013).

[12] Mijalkov, M., McDaniel, A., Wehr, J., Volpe, G., Engineering sensorial delay to control phototaxis and emergent collective behaviors. Phys. Rev. X 6, 011008 (2016).

[13] Palmer, S. E., Marre, O., Berry, M. J., Bialek, W., Predictive information in a sensory population. Proc. Natl. Acad. Sci. USA 112, 6908–6913 (2015).

[14] Sutton, R. S., Barto, A. G., Reinforcement learning: an introduction. MIT Press, Cambridge (1998).

[15] Colabrese, S., Gustavsson, K., Celani, A., Biferale, L., Flow navigation by smart microswimmers via reinforcement learning. Phys. Rev. Lett. 118, 158004 (2017).

[16] Muiños-Landin, S., Ghazi-Zahedi, K., Cichos, F., Reinforcement learning of artificial microswimmers. arXiv 1803.06425v2 (2018).

[17] Gustavsson, K., Biferale, L., Celani, A., Colabrese, S., Finding efficient swimming strategies in a three-dimensional chaotic flow by reinforcement learning. Eur. Phys. J. E Soft Matter 40, 313–7 (2017).

[18] Palmer, G., Yaida, S., Optimizing collective fieldtaxis of swarming agents through reinforcement learning. arXiv 1709.02379 (2017).