Two physicists (a female and male) working on a lab experiment

ALP Seminar: An Accidental Laser and Why We Study It

Seminars and colloquia
Simpkins Lee
Beecroft Building

Dr Jonathan Goldwin
Senior Lecturer
School of Physics and Astronomy, Birmingham University


Seminar series
ALP seminar
Knowledge of physics?
Yes, knowledge of physics required
For more information contact


The advent of the laser revolutionised atomic physics by providing a light source with the spectral brightness to match the intrinsic lineshapes of unperturbed atoms. The strength of light-matter coupling can be further enhanced via confinement within optical resonators. I will describe our experiments with a laser-cooled gas of potassium atoms trapped within a high-finesse ring cavity. As the in-cavity optical depth increases, the regime of collective strong coupling becomes evident as a normal-mode splitting of the cavity transmission spectrum. As the coupling continues to increase, the gas undergoes a transition to lasing driven solely by the cooling and trapping fields. We observe random switching between clockwise and anti-clockwise lasing modes as well as a controllable breaking of symmetry between the two directions. Measurements of photon bunching below the lasing threshold show the coherence time can be extended by two orders of magnitude through a combination of gain and dispersion. Surprisingly (to us), most of these observations will be familiar to professional 'laserists', but in the last part of the talk I will describe our plans to open new horizons for active quantum sensing with cold-atom lasers.