Laura Pérez García defended her PhD thesis on 12 October 2023. Congrats!

A dielectric particle under the influence of the gradient and scattering force. (Image by L. Pérez García.)
Laura Pérez  García defended her PhD thesis on the 12th of October at 13:15. Congrats!
The defense took place in Faraday, Institutionen för fysik, Origovägen 6b, Göteborg.

Title: Advanced methods for the calibration of optical tweezers

Abstract: Optical tweezers have enabled the manipulation of micron-sized particles with great accuracy since their invention by Arthur Ashkin and colleagues in the 1980s. This technique has had an impact in multiple areas, including biology, physics, nanotechnology, spectroscopy, soft matter and nanothermodynamics.
To perform experiments requiring quantitative transduction
of forces with optical tweezers, the optical tweezers need to be calibrated; that is their stiffness needs to be determined. In this thesis, I present the results that I have obtained for the calibration of optical tweezers using probabilistic approaches.
The goal of these approaches is to use the available data most efficiently and even be able to have an estimation of the error associated with the calibration. This is of the utmost importance when one has limited data, as is often the case with systems out of equilibrium, low signal-to-noise ratios, and systems in which the conditions change with time quite fast. This thesis is divided into two problems. The first problem I had was the unavailability of a comprehensive method to measure force fields in extended, non-conservative, and unstable equilibrium points. For this problem I used Bayesian inference in the form of a maximum likelihood estimator, which allowed me to characterize the force field even in conditions previously not possible to tackle. This parameter-free method called FORMA proved to be more precise, accurate, faster, and less data-intensive than the previous conventional method, i.e. equipartition, MSD, ACF, and PSF. Not only that, but it allowed me to characterize the force field generated by Laguerre-Gaussian beams with different orbital/spin angular momentum, a double-well potential, and a speckle pattern.
The second problem I tackled was the error in the estimators due to
limited bandwidth and finite integration time. For this, we developed the joint probability density function of observing the particle at a given set of positions and times. We derived generalized formulas for the calibration methods; these new formulas successfully correct for the overestimation of the stiffness and the underestimation of the diffusion coefficient caused by a finite integration time; it also accounts for the limited sampling frequency and the trajectory length.
In general, this thesis shows the potential of having a probabilistic and inference approach to the problem of deducing the set of parameters that characterize the Langevin equation of motion of a particle from a time series of its position. The solution to this problem has applications not only to the calibration of optical tweezers but also to microrheology, the behavior of single molecules inside a cell, and animal migration.

Thesis: https://hdl.handle.net/2077/78214

Supervisor: Giovanni Volpe
Examiner: Mattias Goksör
Opponent: Balpreet Singh Ahluwalia
Committee: Thomas Huser, Juliane Simmchen, Kirstine Berg-Sørensen
Alternate board member: Mattias Marklund

Presentation by L. Pérez at ELS 2021, 13 July 2021

Laura Pérez presented the work “FORMA and BEFORE: expanding applications of optical tweezers” at the ELS conference (online) on the 13th of July.

The main objective of the Electromagnetic and Light Scattering Conference (ELS) is to bring together scientists and engineers studying various aspects of light scattering and to provide a relaxed academic atmosphere for in-depth discussions of theoretical advances, measurements, and applications.

FORMA allows to identify and characterize all the equilibrium points in a force field generated by a speckle pattern.
FORMA and BEFORE: Expanding Applications of Optical Tweezers. Laura Pérez Garcia, Martin Selin, Alejandro V. Arzola, Giovanni Volpe, Alessandro Magazzù, Isaac Pérez Castillo.
ELS 2021
Date: 13 July 2021
Time: 15:45 (CEST)

Abstract: 
FORMA (force reconstruction via maximum-likelihood-estimator analysis) addresses the need to measure the force fields acting on microscopic particles. Compared to alternative established methods, FORMA is faster, simpler, more accurate, and more precise. Furthermore, FORMA can also measure non-conservative and out-of-equilibrium force fields. Here, after a brief introduction to FORMA, I will present its use, advantages, and limitations. I will conclude with the most recent work where we exploit Bayesian inference to expand FORMA’s scope of application.

Laura Pérez García wins the paper prize student at OSA OMA Biophotonics 2021

Laura Pérez Garcia won the prize for 2021 OSA Biophotonics Congress: Optics in the Life Sciences Student Paper Prize in the OSA-OMA Biophotonics 2021, with the work titled FORMA and BEFORE: expanding applications of optical tweezers.

Presentation by L. Pérez García at OSA-OMA-2021

FORMA allows to identify and characterize all the equilibrium points in a force field generated by a speckle pattern.
FORMA and BEFORE: Expanding Applications of Optical Tweezers. Laura Pérez Garcia, Martin Selin, Alejandro V. Arzola, Giovanni Volpe, Alessandro Magazzù, Isaac Pérez Castillo.
Submitted to OSA-OMA 2021,  ATh1D.5
Date: 15 April
Time: 15:45 (CEST)

Abstract: 
FORMA (force reconstruction via maximum-likelihood-estimator analysis) addresses the need to measure the force fields acting on microscopic particles. Compared to alternative established methods, FORMA is faster, simpler, more accurate, and more precise. Furthermore, FORMA can also measure non-conservative and out-of-equilibrium force fields. Here, after a brief introduction to FORMA, I will present its use, advantages, and limitations. I will conclude with the most recent work where we exploit Bayesian inference to expand FORMA’s scope of application.

Laura Pérez García nominated for a Student Paper Prize at the Biophotonics Congress

FORMA allows to identify and characterize all the equilibrium points in a force field generated by a speckle pattern

Laura Pérez García has been nominated by the Optical Society of America for a Student Paper Prize for Optical Manipulation and its Applications among three other finalists. She will present her work on FORMA and BEFORE: Expanding Applications of Optical Tweezers at the Optical Manipulation and its Applications meeting as part of the 2021 OSA Biophotonics Congress: Optics in Life Sciences.

The final selection will be based on the oral talk and Laura will present her work on the 15th of April at 15:45 (CEST).

Invited talk by L. Pérez at SPIE Photonics West OPTO

Stable, unstable and saddle points in a speckle optical potential.
FORMA: expanding applications of optical tweezers
Laura Pérez García
Invited talk at SPIE Photonics West OPTO
6 March 2021
Online

In this presentation, Laura Pérez will talk about FORMA  (force reconstruction via maximum-likelihood-estimator analysis) which addresses the need of measuring the force fields acting on microscopic particles. Compared to alternative established methods, FORMA is faster, simpler, more accurate, and more precise. Furthermore, FORMA can also measure non-conservative and out-of-equilibrium force fields. Here, after a brief introduction to FORMA, I will present its use, advantages, and limitations. I will conclude with some recent work where we exploit Bayesian inference to expand the scope of application of FORMA.

References:
Laura Pérez García, Jaime Donlucas Pérez, Giorgio Volpe, Alejandro V. Arzola & Giovanni Volpe, High-Performance Reconstruction of Microscopic Force Fields from Brownian Trajectories, Nature Communications 9, 5166 (2018)

Time: 6 March 2021
Place: Online
Link: FORMA: expanding applications of optical tweezers at SPIE Photonics West OPTO

Career Webinar with Christian Reimer: From electro-optics to a start-up company

Christian Reimer, Co-founder and Head of Product at HyperLight and OSA Ambassador

The OSA Student chapter together with FFF will host a career webinar again, this time with Christian Reimer, Co-founder and Head of Product at HyperLight and OSA Ambassador. 

Christian Reimer will give a talk with title: Electro-optics with thin film lithium niobite and what it is like to work at a start-up company.

In the scientific part of his talk, Christian will give an introduction to the field of integrated photonics with thin-film lithium niobate, with a  focus on electro-optic applications, as well as recent progress on transforming the field from chip-based proof-of-concept realizations for wafer-scale production.

In the professional development section, he will then share his experience transitioning from academia to a start-up company. He will talk about differences and similarities in the work environment, what to expect in terms of tasks and responsibilities, and explain how salaries at start-ups can include combinations of equity and incentives.

Christian Reimer´s mini bio:  Dr. Christian Reimer is a physicist and entrepreneur working in the fields of nonlinear optics, integrated photonics and quantum optics. He received graduate degrees from the Karlsruhe Institute of Technology in Germany, Heriot-Watt University in Scotland, and the National Institute of Scientific Research in Canada. He then worked as a postdoctoral fellow at Harvard University, before becoming Co-Founder and Head of Product of HyperLight Corporation. HyperLight, a Venture-Capital funded start-up out of Harvard University, is specialized on integrated lithium niobate technologies for ultra-high performance photonic solutions.

The webinar will be on the 9th of December at 16:30 via zoom.

Registration is required: https://tinyurl.com/reimer-OSA-FFF

New OSA chapter established at Gothenburg University!

Screenshot of the GU-OSA Student Chapter kick-off meeting, autumn semester 2020.

A new student chapter of the Optical Society of America (OSA) has been established at the Physics Department of Gothenburg University!

The founding members of the GU-OSA student chapter are students from the Soft Matter Lab, the Biophysics Group, and Optical Levitation Group, all part of the Physics Department of Gothenburg University. The chapter activity started on the autumn semester of 2020 with the online kick-off meeting, where the future plans and activities of the GU-OSA chapter were discussed.

The Optical Society of America (OSA) supports outreach and networking through the student chapters. So far, there are over 370 Student Chapter across the world organising events such as seminars, colloquiums, and outreach activities focused on increasing awareness of the importance of optics in our daily life and society.

To keep you updated on the GU-OSA student chapter activities, follow us on social media:
Facebook: OSA-GU Student chapter
Instagram: osasc.gu

or contact us via email: osasc.gu@gmail.com

Presentation by Laura Pérez at the OSA Biophotonics Congress, Tucson, 16 Apr 2019

FORMA: Force Reconstruction via Maximum-likelihood-estimator Analysis

Laura Pérez García, Jaime Donlucas Pérez, Giorgio Volpe, Alejandro V. Areola & Giovanni Volpe
OSA Biophotonics Congress, Tucson (AZ), USA
16 April 2019

Microscopic force characterization is often done by using a microscopic colloidal particle which probes local forces. These particles are often held by a harmonic trapping potential with stiffness k so that a homogeneous force acting on the particle results in a displacement Δx from the equilibrium position and the force can, therefore, be measured as k Δx . To perform such measurement, it is necessary to determine the value of k , which is often done by measuring the Brownian fluctuations of the particle around its stable equilibrium position. This is achieved by measuring the particle position as a function of time, x (t) , and then using some calibration algorithms; the most commonly employed techniques are the potential analysis that relies on the fact that the force is derived from a potential; and the power spectral density (PSD) and the auto-correlation function (ACF) methods that require a regular sampling in time. Besides the previous requirements, all methods depend on the choice of some analysis parameters. This has inhibited the applicability of force measurement methods to characterize force fields with non-conservative components or where the particle freely explores an extended potential landscape. We propose a method for Force Reconstruction via Maximum-likelihood-estimator Analysis (FORMA) that exploits the fact that in the proximity of an equilibrium position the force field can be approximated by a linear form and, therefore, optimally estimated using a linear Maximum-likelihood-estimator (MLE).

Session: Biological Applications
10:30 AM–12:00 AM, Tuesday, April 16, 2019

More information can be found on the link: https://www.osapublishing.org/abstract.cfm?uri=OMA-2019-AT2E.2

 

Laura Pérez-García joins the Soft Matter Lab

Laura Pérez-García starts her PhD at the Physics Department of the University of Gothenburg on 15th November 2018.

Laura has a Master degree in physical sciences from Universidad Nacional Autónoma de México in México City, where she submitted a Master thesis about optical forces in speckle fields.

The aim of her  PhD project is to study the behavior of active matter using Light Sheet Microscopy.