Laser Spectroscopy
Short description
The laser spectroscopy research group is active in four different research areas, all involving the use of lasers. Members of the group operate both the laser laboratory GPF, (Gothenburg Photon Factory) and the ion beam facility GUNILLA (Gothenburg University Negative Ion Laser Laboratory). The group consist of Swedish and international students and researchers. In addition to the in-house research activities, the group participates in experiments at national and international research facilities. For example DESIREE at Stockholm University and at CERN in Switzerland.
1.1 Laser spectroscopy of negative ions
Negative ions are unique quantum systems. The lack of a long-range Coulomb force causes the inter-electronic interaction to become relatively more important. Consequently, the independent particle model, that adequately describes atomic structure under normal conditions, breaks down. Experimental studies of negative ions can therefore serve as a useful probe of electron correlation and hence be used to test theoretical models that go beyond the independent particle approximation.
The overall goal of our research is to increase the fundamental understanding of atomic and molecular negative ions and their interaction with light. The research is conducted using the in-house accelerator GUNILLA and the double storage ring DESIREE located at Stockholm University. Radioactive negative ions are studied at the rare isotope facility ISOLDE at CERN in Switzerland. Finally, we are involved in the development of techniques to improve Accelerator Mass Spectrometry (AMS), which is the most sensitive trace element method. This project is performed in collaboration with researchers at the VERA facility at the University of Vienna.
1.1.1 Fundamental properties of negative ions
The ion beam facility GUNILLA (Gothenburg University Negative Ion Laser Laboratory) consist of a negative ion source, a sector magnet and three different experimental beamlines. This allows us to study essentially all stable negative ions by letting them interact with one or multiple of the frequency tunable high-power lasers available in our lab.
The facility is equipped with detectors for neutral atoms, positive ions and electrons that have been produced in single or double photodetachment processes. We use those to measure electron affinities, photodetachment cross sections and angular distributions of electrons emitted in the photodetachment process. The aim of the research is to increase our understanding of atomic and molecular systems by increasing our knowledge about electrons interacting in an atomic system.
1.1.2 Studies of negative ions of radioactive isotopes
ISOLDE (Isotope Separator OnLine DEvice) at CERN in Switzerland is an online facility for the production of radioactive isotopes. A 1.4 GeV proton beam impinges on a target of e.g. uranium carbide, resulting in the production of a wide range of radioactive isotopes with half-lives as short as a few milliseconds. Those isotopes diffuse into an ion source, where they are ionized. Negative ions are then extracted, accelerated, mass analyzed, and finally guided to different experimental end-stations, similar to GUNILLA.
Our group uses the ISOLDE facility to measure electron affinities of radioactive isotopes. A major achievement was the measurement of the electron affinity of astatine, which is the least abundant element on earth. Astatine is of great interest for a cancer treatment called Targeted Alpha Therapy (TAT), where our measurement contributed crucial information about the chemical properties of astatine towards its use in treatment. In addition to the EAs of rare isotopes, at ISOLDE we can also study isotopes shifts in electron affinities and have started a collaboration for efficient negative ion production with the local teams using the charge exchange process.
For the studies at ISOLDE, we have built a dedicated detector, GANDALPH (Gothenburg ANion Detector for Affinity measurements by Laser Photodetachment), where the radioactive negative ion beam is overlapped with a laser beam. Neutral atoms produced in the photodetachment process are then detected utilizing a neutral particle detector.
1.1.3 Storage of negative ions at extremely low pressures and temperatures
DESIREE (Double ElectroStatic Ion Ring ExpEriment) is a world-wide unique facility for studies of atomic and molecular collisions. Positive and negative ions can be stored in two storage rings with a common collinear section. The temperature of the facility is 13 K and the pressure is 10-14 mbar, resembling the conditions in outer space. There are only three cryogenic storage rings globally, and DESIREE is the only double storage ring. Since the 1st of January 2018, DESIREE is a national infrastructure facility supported by the Swedish Research Council, hosted by Stockholm University and operated jointly by Stockholm University, University of Gothenburg and Malmö University. We are using DESIREE to study life times of bound excited states in negative ions and to perform high precision measurements of electron affinities, such as the EA of oxygen, which is presently the EA determined with highest precision.
1.1.4 Mass spectroscopy
Accelerator Mass Spectrometry (AMS) is the most sensitive trace element method with demonstrated detection limits down to the 10-18 level. The most well-known application of this method is 14C - dating. We are collaborating with researchers at VERA (Vienna Environmental Research Accelerator) to improve the sensitivity of this method by incorporating laser spectroscopic techniques in the mass spectrometer. Investigations of atomic and molecular negative ions of interest in mass spectroscopic applications are conducted at the GUNILLA facility in Gothenburg or at DESIREE in Stockholm. The results from these studies will then be implemented at the VERA facility. An example is our campaign to investigate the EA of tungsten, hafnium and their respective pentafluoride molecules in order to determine the concentration of Hf in samples used to investigate processes the early solar system.
1.2 Optical levitation
Optical manipulation was first demonstrated by Arthur Ashkin in 1971 (App. Phys. Lett. 19 (1971) 283) at Bell Labs when he levitated glass beads using a very powerful continuous wave laser. His group later developed the single beam gradient trap also called the laser tweezers (Ashkin et al. Opt. Lett. 11 (1986) 288) which very soon became the standard tool in optical manipulation, mainly due its applicability in microbiology. In recent years a renewed interest in the technique of optical levitation has occurred, and we are currently involved in several research projects using this method.
1.2.1 Directional Mie scattering spectroscopy of evaporating droplets
Mie scattering occurs when a dielectric sphere scatters a plane wave, as is the case of liquid droplets in an optical trap. The scattering spectrum can be obtained by varying the laser frequency or the sphere size, producing a complex signal with precise information about the droplet size and refractive index. Using optical levitation, we trap droplets and measure the scattering as they evaporate, resulting in a rich spectrum with many resonances arranged in a series of combs. This movies shows how a drop is trapped, and how the scattering intensity if varying as the droplet evaporates.
This signal, having Q-factors of up to 104, provides a new technique to measure the evaporation rate and composition of evaporating droplets down to the micrometric regime. We are now using it to measure the evaporation rate of fuels and biofuels and plan to use it to measure solvents with polymers and mucins.
1.2.2 Particle dynamics in water, air and vacuum
Many phenomena can be understood through the study of their energy potentials, including chemical reactions, molecular vibrations, and thermodynamic processes. However, varying these potentials can be hard or even impossible. Instead, we study the behavior of particles trapped in optical traps where we have full control over the energy potential. Furthermore, having these traps in air and vacuum gives us additional control over the damping force.
To this purpose, we have a series of different optical traps including and optical tweezers setup to trap diatoms (unicellular organisms), a double vertical trap to study the dynamics of spheres and dumbbells in a double potential well under varying pressures, and a counter propagating trap in vacuum to study the dynamics of nanoparticles in a sinusoidal potential. Upcoming research using these setups includes spectroscopical measurements of single-cell biological samples, the study of the Kramers turnover, and the cooling of particles in time varying, periodic potentials.
1.2.3 Mass limited nanotargets
In collaboration with Umeå university, we study the interaction between extremely short (attoseconds) and extremely intense (1022 W/m2) laser pulses with matter. The interaction is so strong, that it tears off the electrons, resulting in highly energetic electron bunches. We are building a high repletion nanoparticle loader into vacuum. These particles will be exposed to attosecond pulses to generate consistent electron bunches.
1.3 Teaching Experimental physics
In this project we try to bridge the gap between experimental research conducted at a university with the physics taught in high schools. Our main goal is to develop modern experiments and physics demonstrations that are used either at visits to our laboratory or as remotely controlled laboratory exercises. The research is made in closed collaboration with the research group Physic Education Research (PER).
1.3.1 Teaching optical levitation
As an example, we have developed an optical levitation experiment.
A vertically aligned electrical field (AC and/or DC) can be applied over the trapped droplet, and it can be exposed to UV-light or a radioactive source. The students can use this set-up to observe various phenomena with their own eyes as the only detector. They can measure the size of the droplet by observing diffracted light. The charge of the droplet can be measured by detecting its motion in an applied electric field, and the photoelectric effect can be studied by observing how electrons are released when the droplet is exposed to UV radiation. This set-up is used to demonstrate very fundamental processes using an experiment which have great similarities with the traps used for atom cooling, which are existing only in the most advanced atomic physics laboratories. We have used this setup do demonstrated single droplet Milikan experiment, where we can observe the emission of single electrons.
1.3.2 Teaching quantum mechanics
When analyzing the light scattering of a droplet, we found a striking similarity in the resonances that make it twinkle to the energy levels of an atom. This is because the droplet forms a spherical well potential for photons, like the potentials commonly taught in a quantum mechanics course. In this project we are building up this analogy to be used in quantum mechanics teaching. This includes generating and plotting spectra of scattering droplets, investigating the analogies to fundamental physics concepts, creating a teaching module, and implementing it in a classroom.
1.3.3 Trapping reflecting particles
We are developing an optical levitation system to be used to levitate and investigate a broader spectrum of particles than just transparent spherical ones, which has been the most common one to levitate in the past. By changing the geometry of the laser beam, we are now able to levitate a broad range of particles, for example polystyrene spheres, lycopodium spores and micrometer sized aluminum particles, both spherical and irregular ones. With the use of a high speed camera, we study their behavior and a UV-light source can be used to manipulate their electrical charge. We now aim to design a system where we can detect single electron emission in the photoelectric effect.
1.4 Micro bubble generation
Microbubble generation is of vital importance in many applications ranging from medical diagnostics, water purification to food industry. Within these fields bubbles are typically generated using ultrasound or mechanical agitation. These methods are very efficient, but they generate bubbles without control of position or size. However, research on bubble formation require that individual bubbles can be produced with detailed control. This can be achieved by focussing a femtosecond laser beam into a liquid, and this technique has hence been developed into a very active research field. These studies are typically performed in the bulk of a liquid, whereas many important applications, such as bubble formation in a blood vessel, occurs in a confined environment. In this project we study laser induced bubble formation in a microchannel system where we can control the channel width. By implementing two optical traps so we can trap and then move the generated bubbles. With this we aim to increase the understanding of bubble formation in confined environments, which will have implications on many important applications.
1.5 Femtosecond laser bone microtomy
The group of Professor Mikael Sigvardsson at Department of Biomedical and Clinical Sciences (BKV) and Division of Molecular Medicine and Virolog (MMV), Linköping University, is a world leading research group in the field of medical molecular biology. The main focus of their research is how to develop bone marrow stem cells into mature cells with several different functions, which will increase the possibilities to treat different disorders in bone marrow function without damaging other tissues and organs. This would also lead to a revolutionary approach in cancer treatments, e.g., leukemia. Recently, we have initiated a collaboration with his group, where we combine their knowledge with our competence in the field of lasers. Our aim is to develop a femtosecond laser microtomy for bone sectioning. Intense laser pulses in the time range of few hundred femtoseconds are focused down to a micrometer sized spot. Due to the extreme intensity at the focus, multi-photon absorption causes ionization of the tissue, i.e., optical breakdown, leading to the formation of a plasma. The fast expansion of the plasma causes disruption and cutting of the bone sample. The duration of the laser pulse is so short that there is no thermal and shock wave induced collateral damage of the surrounding tissues. Of particular interest in this project is the fresh bone sectioning, where vulnerable living cells shall be preserved for post bone cell culture. Meanwhile, this project also attracts attention from osteoporosis research group at Institute of Medicine, Sahlgrenska University Hospital and we look forward to joining hands future research collaborations.
Members
Dag Hanstorp, Professor
Di Lu, Dr., Researcher Engineer
David Leimbach, Dr. Postdoc
Julia Sundberg, Ph. D. student
Javier Tello Marmolejo, Ph. D. student
Miranda Nichols, Ph. D. student
Oscar Isaksson, Fil. Lic.
Frequent visitors
David Pegg, Visiting professor (University of Tenneesse)
Remigio Cabrera Trujillo, Visiting professor (Autunomous National University of Mexico)
Ricardo Méndez Fragoso Visiting professor (Autunomous National University of Mexico)
Uldi Berzinsh, Visiting professor (University of Lativa)
Undergraduate students
Aishwarya James (visiting Master student from CUSAT in India)
Valeria Zuñiga Pérez (visiting Master student from UNAM in Mexico)
Ilse Kardasch (visiting Master student from UNAM in Mexico)
Erik Goksör (project student)
The positions given is either the first position after leaving our group or the current position.
3.2 Ph. D. Students (in order of appearance)
Ph. D. Ulric Ljungblad
Research & Development Manager, Freemelt AB
www.freemelt.com
Freemelt is a startup in additive manufacturing that is developing an open source powder-bed 3D-printer optimized for material development.
Ph. D. Andreas Klinkmüller
Assekuradeur GmbH
www.deutsche-assekuradeur.de
Ph. D. Gunnar Haeffler
Team Manager Drug Product Manufacture, Astra Zeneca
www.astrazeneca.com/
Team Manager within an R&D function that manufactures drug products under development for use in clinical trials.
Ph. D. Jonas Enger
University Lecturer, University of Gothenburg
www.physics.gu.se
Teacher and researcher with specific responsibility for teacher training program and educational development.
Fil. Lic. Petter Hagberg
Technology Strategy & Planning Manager Volvo Group Trucks Technology
www.volvogroup.com
Working with strategic planning mainly focused on long term global technology strategies and the Volvo Group Technology Plan, and coordination of the research investment portfolio for the Trucks business.
Ph. D. Karin Fritioff
Senior Specialist, Vattenfall
www.vattenfall.se
Radiological protection specialist with focus on radiological consequence assessments, radiation shielding calculations and nuclear emergency preparedness and response.
Ph. D. Joakim Sandström
Senior Lecturer, Department of Engineering, University of Borås
www.hb.se
Lecturer in physics and mathematics.
Ph. D. Mattias Goksör
Profesor, Pro-Vice Chancellor, University of Gothenburg
www.gu.se
Supports the Vice-Chancellor in providing academic leadership to the University, and work in partnership with senior administrators to help drive strategy and policy development.
Ph. D. Kerstin Ramser
Professor, Luleå University of Technology
www.ltu.se
Professor in experimental mechanics with focus on real time optical spectroscopy, imaging, optical manipulation and microfluidics.
Ph. D. Pontus Andersson
Emissions Assessment and Instrument Development, FluxSense AB
www.fluxsense.se
Measurements of diffuse emission of VOC from primary petrochemical industries using a variety of optical absorption spectroscopy techniques. Instrument hardware development.
Ph. D. Anton Lindahl
Senior Software Designer, Qamcom Research & Technology
www.qamcom.se
Software development with focus on data analysis and algoritms but always close to the hardware and the application. Projects contain for example radar development, Klaman filtering, embedded systems, medtech and image processing.
Ph. D. Hannes Hultgren
System Architect, RaySafe AB
www.raysafe.com
System Architect developing X-ray sensors. Focusing on the physical detection methods and the mathematical algorithms needed to calculate the desired parameters.
Impact Unified AB, Co-founder
www.impactunified.com
We are a gaming studio doing impact based games, VR-experiences and documentaries. We are trying to make the world a better place through education and awareness.
Ph. D. Johan Rohlen
Software Configuration Specialist, Jeppesen Systems AB
ww1.jeppesen.com
Working with processes and automation of delivering software. Especially interested in bridging the gap between software developers and customers.
Ph. D. Mikael Eklund
R&D Engineer, Siemens Building Technologies, Zug, Switzerland www.buildingtechnologies.siemens.com
R&D Engineer sensor technologies for multi-criteria fire detectors and comfort sensors.
Ph. D. Jakob Welander
https://www.ri.se/sv
Ph. D. Ademir Aleman
https://www.gu.se/en/research/spintronics
Post doc
Ph. D. Annie Ringwall Moberg
https://www.ri.se/sv
3.2 Postdocs
The positions given is either the first position after leaving our group or the current position.
Ph. D. Uldis Berzinsh, Lecturer,
Univeristy of Latvia
https://www.lu.lv/en/
Ph. D. Igor Kiyan, Researcher,
Freie Universität Berlin
http://www.physik.fu-berlin.de
Ph. D. Gerry Collins, Research Fellow
The 14Chrono Centre, Queens University Belfast
http://www.chrono.qub.ac.uk/
Ph. D. Peter Klason, Researcher
RISE Research Institutes of Sweden
www.ri.se
Ph. D. Anette Graneli, Group Manager
RISE Research Institutes of Sweden
www.ri.se
Ph. D. Besira Mihiretie, Researcher
Hot Disk AB
http://www.hotdiskinstruments.com/
Ph. D. Vijay Muthu, Postdoc
Bangalore, India
Ph. D. Soumya Radhakrishnan
India
Ph. D. D. Chaitanya Kumar Rao, Researcher
IIT Kanpur
https://www.iitk.ac.in/
Ph. D. Yogeshwar Mishra, Researcher
KAUST university, Saudi Arabia
https://www.kaust.edu.sa/en/
VERA (Vienna Environmetal Research Accelerator)
http://isotopenforschung.univie.ac.at/
The LARISSA group at University of Mainz
The ISOLDE facility at CERN
http://isolde.web.cern.ch/
The DESIREE facility Stockholm University
http://www.fysik.su.se/
The Spintronic research group at University of Gothenburg
https://www.gu.se/en/research/spintronics
Gothenburg Photon Factory
The Gothenburg photon factory is equipped with a wide range of fixed as well as tunable wavelength lasers. There are continuous wave lasers and pulsed lasers ranging from nanoseconds to femtoseconds. It is one out of three laboratories that constitutes the network Laserlab Göteborg (LLG), which in turn is part of the Swedish network Laser Lab Sweden (LLS). The list below shows the lasers available at Gothenburg photon factory:
- High rep-rate Ti:Saphire Laser (Laser Quantum, <30fs, 1 GHz, 800 nm)
- YAG Pumped OPO-system (Spectra Physics, 6ns, 10 Hz, 220-2000 nm)
- YAG Pumped OPO-system (LaserVision 6ns, 10 Hz, 1350-5000 nm)
- Femtosecond laser system (Clark, 30 fs, 1 kHz, 470-1600 nm)
- Narrow bandwidth Ti:Saphire laser (Home built, 100 ns, 7 kHz, fundamental + frequency doubled light)
- YAG-Pumped dye laser (Sirah, 6 ns, 10 Hz, 300-900 nm)
- 3st high power diode lasers (Laser quantum,cw 2 W, 2 st 532nm, 1 st 660 nm)
- YAG and dyelaserpumped DFG/OPA-system (Sirah, 2600-3600 nm och 5500-7100 nm)
The GUNILLA ion beam facility
Our in-house studies of negative ions are conducted at the experimental facility GUNILLA (Göteborg University Negative Ion Laser LAboratory), which is a negative ion accelerator with three beamlines. Negative ions are produced in a sputter negative ions source, mass selected in a 90° degree sector magnet and finally directed into one of three beam lines. The first is a collinear interaction equipped with a neutral particle detector. An electric potential can be applied to its interaction region in order to Doppler tune the frequency experienced by the ions. The second beamline is equipped with the angular resolved electron spectrometer PEARLS (Photoelectron Angular Resolved Linear Spectrometer). The third beamline, finally, is designed for studies of highly excited doubly excited states and double detachment studies. It is equipped with a field ionizer, an electrostatic analyzer and a position sensitive detector.
Below follows some of the technical specifications of GUNILLA:
- Ion source: Peabody sputter ion source
- Beam energy: 3-6 keV
- Mass resolution: 400 for atoms and 700 for molecules
- Vacuum: 10-9 mbar in detection regions
- Interaction regions: Crossed and collinear interaction regions
- Detectors: Neutral particle detector, Beam scanners, Faraday cups, RoentDek Time and Position sensitive MCP Delay Line Detector.
We can offer a large variety of Bachelor and Master projects within the large framework of the research projects described above. The projects can be conducted in our laboratories in Gothenburg or at the external facilities where we perform our research, i.e. the ISOLDE facility at CERN, the DESIREE storage ring at Stockholm University or at the VERA accelerator in Vienna. If you are interested in a project: please contact any of us in the group and we can tell you what we can offer.