Faculty Directory

O'Shea, Patrick G.

O'Shea, Patrick G.

Distinguished Scholar-Teacher
Electrical and Computer Engineering
Institute for Research in Electronics & Applied Physics
3301 A.V. Williams Bldg.

Latest publication: Design Considerations for Compact High-Average Power Free-Electron Lasers/Masers at Terahertz Frequencies

Abstract:  Interest is increasing in high-power terahertz (THz) sources of radiation. The terminology is fluid, but researchers in the field typically refer to frequencies ranging from about 300 GHz to 10 THz as THz radiation. In this article, we present a description of design considerations for a compact, high-average power free-electron laser. At present, THz radiation is generated by a variety of mechanisms, including laser-based sources and electron-beam-based sources. We provide a short description of current THz source technology to give background against which to compare the present concept; however, this should not be considered a comprehensive discussion of such technologies.

I'm looking for a student to work on Quantum Aspects of Bright Electron beams for X-ray Free-electron Lasers 

A recent presentation by graduate student Liam Pocher won a best student paper award at NAPAC22

See details, and watch Liam's presentation under the Publications tab above


Bright Beams at Work News:

High Energy Physics

US particle physicists envision the future of the field


Cancer Treatment:

How radiotherapy became a lifesaver – from X-rays to the proton beam

Will Proton Therapy Market Reach $1.6 Billion by 2031?

New Discoveries:

CERN's Large Hadron Collider poised to unlock more secrets of the universe

Exciting discovery from CERN

5 Myths About Patricle Acelerators 

Making Smaller Accelerators

Unresolved questions: Does warm water freeze faster than cool water?

Quantum News

A flock of birds exhibiting swarming behavior ( photo by D. Dibenski)


Space Charge Dreams (photo  by Chip Simons)


Professor O'Shea is Principal Investigator in the Bright Beams Collective Research Group

He was born in Cork, Ireland, and holds a BSc degree in Experimental Physics from the National University of Ireland, University College Cork, and an M.S. and Ph.D. in Physics from the University of Maryland.

In recognition of significant achievements in education and research, he has been elected a Fellow of the Royal Society for the Arts,  American Association for the Advancement of Science, American Physical Society, Institute of Electrical and Electronic Engineers,  Irish Academy of Engineering, and won the University of Maryland's Distinguished Scholar-Teacher Award.

Professor O’Shea’s technical expertise lies in the field of applied electromagnetics, nonlinear dynamics, and charged particle beam technology, and applications.

Professor O'Shea has previously served as:


  • Royal Society for the Encouragement of Arts, Manufactures, and Commerce (RSA), Fellow 
  • American Association for the Advancement of Science, Fellow
  • Irish Academy of Engineering, Fellow
  • American Physical Society, Fellow
  • Institute for Electrical and Electronic Engineering, Fellow
  • Distinguished Scholar-Teacher, University of Maryland 
  • Phi Kappa Phi Honor Society
  • President Emeritus, University College Cork



The University of Maryland Electron Ring (by Tim Koeth)

Prof O'Shea's current research is in the area of charged particle beam technology, electromagnetics, and their applications.


  • Demonstrated space-charge limited current phenomena in the propagation of high-current low energy electron beams in solenoidal and gas-focused regimes
  • Demonstrated and studied an advanced accelerator concept known as the laser-controlled collective ion accelerator. Achieved an accelerating gradient for protons of 30 MV/m
  • Developed record high brightness 1-MeV H-, and Ho beams on Beam Experiments Aboard Rocket (BEAR) test stand.
  • Demonstrated autonomous operation of a directed energy experiment in space using radio-frequency quadrupole H- accelerator. Studied propagation Ho, H-, and H+ beams in geomagnetic field at an altitude of 200 km
  • Demonstrated a high-current radio-frequency photocathode electron source as a driver for a high-gain infrared free-electron laser - first operation of a high-current RF photoinjector coupled to a linear accelerator.
  • Demonstrated operation of electron photoinjector with space-charge emittance compensation whose brightness exceeded that of conventional sources by two orders of magnitude. Experimental confirmation of the theory of space charge emittance growth compensation.
  • Demonstrated free-electron lasing from 370 nm to 11 µm using low-energy, high-brightness electron beam, and achieved a record short wavelength for a linear accelerator-driven FEL
  • Member of the team that demonstrated inverse Compton γ-ray production using an FEL
  • Developed a theory of reversible and irreversible emittance growth
  • Electron beam production of medical radioisotopes
  • Developed the nitrogen-laser driven RF photoinjector
  • Compact electron ring (UMER), an analog computer for beam physics studies in the space charge dominated regime; thermodynamics of beams and energy transfer mechanisms in beam systems. Discovery of solitary waves in electron beams.
  • Developed dispenser photocathode electron source.

Bright Beams Collective

Our aim is to understand how to make brighter charged particle beams. A bright beam typically has a large number of charged particles (electrons or ions) that are collectively interacting.  The collective dynamics of these beams are fascinating. We are particularly interested in beams where the self-forces resulting from space-charge are very strong. They exhibit nonlinear phenomena such as solitary waves (solitons). Understanding beam swarms and how to control them is essential for many diverse applications, such as creating light where there is darkness in the electromagnetic spectrum,  cancer treatment, radiographic imagingtomography high-energy-density physics, inertial fusion energy; and galactic dynamics.

The group began exploring space-charge-dominated beams (intense swarms) in the 1980s under the direction of my Ph.D. co-advisor, the late Professor Martin Reiser.