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1964 …2023

Research activity per year

Personal profile


Emeritus Professor Brian Orr (BSc Hons I, Sydney, 1964; MSc, Sydney, 1965; PhD, Bristol, UK, 1968; FRACI, FAIP, FOSA) has since 2003 been based in Macquarie University’s Department of Physics and Astronomy. He had previously held an 18-year academic appointment at the University of NSW before moving to Macquarie University as Professor of Chemistry (1988–2002). His administrative roles there have included service as Head of School/Department (1989–92/1999–2002), as Deputy Chair of the Academic Senate (1989–92), and as a member of the University Council (1999–2002). He is Founding Director (2007–2010) of MQ Photonics – a University Research Centre incorporating the former Special Research Centre for Lasers and Applications, of which he was Deputy Director (1988–2002) and then Director (2003–07).

Brian's research covers experimental and theoretical topics in molecular and optical physics, most of them applying lasers and spectroscopy to areas such as molecular energy-transfer processes, high-resolution spectroscopy, photochemistry, chemical analysis, nonlinear optics, optical-cavity signal enhancement, photonic techniques, and laser-based instrumentation. He has long been involved in several professional chemical, optical and physical societies and has been active in journal editing (Optics Express, JOSAB, and Chemical Physics Letters). He was the first recipient (in 1994) of the Royal Australian Chemical Institute's Physical Chemistry Division Medal. In 2004, The Optical Society of America (OSA) awarded him its prestigious William F. Meggers Award “for outstanding work in spectroscopy.” In 2005, he received the Australian Optical Society's W.H. (Beattie) Steel Medal.

Several of Brian’s early research publications have become classics in their fields. For instance, his 1971 paper with J.F. Ward derived what has become a standard formulation of nonlinear-optical susceptibilities (which are intrinsic to optical telecommunications); it has received more than 1500 citations. Likewise, Brian’s 1970 paper with A.D. Buckingham and J.M. Sichel, presenting a quantum-mechanical theory of rotational-state-resolved molecular photoelectron spectroscopy, has been cited more than 250 times. Much more recently, Brian has been active in applied research, developing novel optical sensing methods to monitor agriculture, livestock, wastewater treatment and the atmospheric environment.

According to Google Scholar (8 August 2021 - with a few early papers missed), Brian’s whole-of-career research publications performance is: h-index = 39; i10-index = 107; total citations = 6412 (786 since 2016).

Representative recent research publications by Brian and his colleagues are as follows:

M.Kono, Y.He, B.R.Lewis, S.T.Gibson, K.G.H.Baldwin and B.J.Orr, “Two-photon excitation of two Rydberg levels of O2 above 95 130 cm–1: rotational state dependence of predissociation linewidths,” Journal of Quantitative Spectroscopy and Radiative Transfer 244, 106841/1–106841
/10 (2020).
The latest paper in a series that uses our own high-performance nonlinear-optical ultraviolet light source for ionisation-detected studies of high-resolution sub-Doppler atomic and molecular spectra.

• B.J.Orr, “Collision-induced rovibrational energy transfer in small polyatomic molecules: the role of intramolecular perturbations,” Molecular Physics 116, 36663700 (2018).
This wide-ranging invited review 
paper covers experiments and mechanisms concerning the role of intramolecular perturbations in enhancing (or suppressing) the efficiency of rotationally resolved vibrational transfer in rovibrational manifolds of small polyatomic molecules, such as CO2, D2CO and C2H2.

• Y.He, B.J.Orr, K.G.H.Baldwin, R.B.Warrington, M.J.Wouters, A.N.Luiten, P.Mirtschin, T.Tzioumis, C.Phillips, J.Stevens, B.Lennon, S.Munting, G.Aben, T.Newlands and T.Rayner, “Long-distance telecom-fiber transfer of a radio-frequency reference for radio astronomy,” Optica 5, 138–146 (2018).
A major ARC-funded consortium has devised reliable, efficient ways to transmit a highly stable frequency reference shared by widely separated radio telescopes, enabling the signals from the facilities to be aligned in time and combined coherently as is necessary for very-long-baseline interferometry (VLBI).

• B.J.Orr, J.G.Haub, Y.He and R.T.White, “Spectroscopic applications of tunable optical parametric oscillators,” in Tunable Laser Applications, 3rd edn., ed. F.J.Duarte (CRC Press, New York, 2016), Ch. 2, pp. 17–142 (incl. 666 references; ISBN 9781498788144); this is a substantial update of corresponding chapters in 1st & 2nd editions (1995 & 2009).
A comprehensive review of the nonlinear-optical theory, instrumental design and frequency-control strategies for tunable optical parametric oscillators (OPOs), with emphasis on their spectroscopic applications.

• Y.He, C.Jin, R.Kan, J.Liu, W.Liu, J.Hill, I.M.Jamie and B.J.Orr, “Remote open-path cavity-ringdown spectroscopic sensing of trace gases in air, based on distributed passive sensors linked by km-long optical fibers,” Optics Express 22, 13170–13189 (2014).
The latest paper in a series using rapidly swept cavity-ringdown spectroscopy for optical-fibre-coupled measurements of gas-phase molecules in industrial, biomedical, agricultural and environmental situations.

For more details of research by Brian Orr and his colleagues within the MQ Photonics Research Centre’s Molecular and Optical Physics Laboratory (MOPL), please visit

Contact Brian Orr:
E-mail ; Mobile (+61)411 240 812; Office in Building 7WW, Room 2.208.


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