PhD Defense by Mikkel Tang

Superradiant Lasers Based on Strontium-88

In superradiant lasers the emitted light has a frequency determined mainly by atoms, as opposed to ordinary lasers, where mechanical parts have a large influence. And while me- chanical parts are hard to replicate and control exactly, the universal properties of atoms are ideal to use as references for precision measurements. In this sense, photons emitted by an atom are a ”frequency ruler” which we can compare other photon frequencies to. Therefore superradiant lasers are a promising technology within quantum metrology, as the best fre- quency references today are limited by tiny thermal disturbances in mechanical mirrors. And even though frequency is the quantity we can measure most accurately, it can also be used as proxy for many other quantities, such as length or gravitational acceleration. Therefore a wide range of areas such as timekeeping, geopositioning and geodesy may benefit from the development of superradiant lasers. Today, this is still an emerging technology, confined to big machines in research labs.  

In this thesis we investigate superradiant lasing in different settings, using the 7.48 kHz- wide 1S0-3P1 electronic transition in strontium. This magnitude of linewidth implies that superradiant lasing is relatively easy and less technically demanding to realize, compared to on the much narrower transitions which are considered in other labs. Similarly, a relatively high power can be realized. The drawback is that narrower transitions may allow for a narrower laser linewidth and lower sensitivity to mechanical disturbances, quantified by the cavity pulling coefficient.