The Cold Molecule Group

During Jionghao Cai's visit to the institute in February, we were able to demonstrate convincing laser slowing of our buffer gas beam of AlF molecules. Starting from an initial velocity of 160m/s, we applied chirped frequency laser slowing to decelerate our molecular beam to about 90m/s. This is approximately halfway the expected capture velocity of a deep ultraviolet magneto-optical trap. Well done Jionghao! 

Congratulations to Simon Hofsäss, who successfully defended his PhD thesis “Laser cooling of atoms and molecules in the deep ultraviolet”, at Radboud University (Nijmegen). His thesis describes experiments demonstrating optical cycling in AlF molecules and magneto-optical trapping of cadmium atoms, taking on the challenges of working with deep ultraviolet laser light. Simon has been a member of the AlF group almost from the beginning and many of our results have relied upon his hard work. Well done Simon! 

Whilst AlF can be made very efficiently in an effusive molecular beam, such a source requires around 1000K and therefore makes using such a source in trapping experiments challenging. Recently, we observed buffer gas cooling of our continuous beam of AlF molecules by injection into a buffer gas cell containing cold Neon. We hope to improve this source and make it suitable for loading a magneo-optical trap in future. 

Cadmium atoms serve as an ideal test system for laser cooling and trapping of AlF molecules. We have tested chirped laser slowing of our Cd buffer gas beam using deep ultraviolet laser light, showing efficient slowing down to 20m/s. This method of laser slowing is commonly used to load magneto-optical traps of molecules. 

David Röser, a graduate student at the University of Bonn and a UVQuanT collaborator, visited us for two weeks to measure isotope shifts in atomic Zn using our buffer gas beam. He brought along an ultrastable Menlo ORC cavity, with which we were able to ensure a narrow laser linewidth (~10 kHz) and highly linear detection laser scan.

Congratulations to Max Doppelbauer, who successfully defended is his PhD thesis at Radboud University, Njimegen! Max's thesis is titled "The AlF molecule as a candidate for laser cooling and trapping”, and brings together much of the work in the group over the past five years. He will continue to work as a Postdoctoral Researcher in the group. 

Whilst AlF can be produced at high temperatures via a chemical reaction, this method has so far not been used to generate a continuous molecular beam in our group. After a few different attempts, we found a method of generating a stable beam of AlF molecules capable of operating for several days. This enabled us to take a 2 THz-wide spectrum of the rovibrational structure of the A-X transition with a precision of 10 MHz, containing an enormous amount of information (more than 300 resolved rovibrational lines!). We hope that this source will prove useful for further experiments with AlF.

We are excited to have Russell Thomas from the UK joining the institute, where we will work as a laser engineer in our group and support others across the Molecular Physics department. He has extensive extensive experience in installing, testing and optimising DUV laser systems relevant for laser cooling AlF molecules. Welcome Russell!

As part of an investigation into molecule production in buffer gas sources, we produced a beam of cold MgF molecules in the same machine we use to generate AlF. Like AlF, MgF is a laser cooling candidate, but much less is known about its first electronically excited state. We undertook a study to measure the rotational and hyperfine structure of the first electronically excited state, and its dipole moment. We found that excited states of opposite parity are much closer in energy than would be naively expected, and this has consequences for optical cycling with MgF.

We are delighted that Jose Eduardo Padilla-Castillo from Cozumel, Mexico has joined us as a new PhD student. Eduardo completed his Masters at Mexico City studying quantum degenerate gases of ⁶Li₂ Feshbach molecules, making the first Bose Einstein Condensate ever produced in Mexico. He will work on laser cooling and trapping of cadmium atoms and AlF molecules. Welcome Eduardo!

We loaded our first magneto-optical trap (MOT) of cadmium atoms, by direct loading from a cryogenic buffer gas beam. We are able to separately trap all stable isotopes using the strong deep ultraviolet transition near 228 nm. This is a convenient test platform for future experiments on the AlF molecule. 

We have designed and assembled an upgraded cryogenic molecular beam source. This enables faster thermal cycling of the machine, more detailed measurements of the molecules in and outside of the buffer gas cell, and straightforward comparison of the production efficiency of various species.