CsYb Project: Gallery
High magnetic field coils

The Feshbach resonances between Yb and Cs has been calculated to occur at quite large mangetic field strengths, between 1000-5000G. Unfortunatley, the wider resonances are thought to occur at the higher fields and so a set of coils will be needed to reach high magnetic fields, but with a stability of milligauss. This is a very hard task, but the first iteration of coils have been designed and wound that will allow us to get to approximately 1000G. These coils will allow us to try to see the Feshbach resonances at lower fields and this will allow us to consider whether we need a more complicated design afterwards.

The coil set comprises of four pairs of coils, some of which provide magnetic field gradients and some which give us the large bias fields we require. They will sit inside the re-entrant flanges over the science chamber and will be clamped into place to avoid movement of the coil pairs as they try to repel eack other.

Yb spectroscopy

The Yb beam machine gives the following spectra for Yb. The left hand graph shows the fluorescence on the 556nm transition. Signals due to each of the more abundant stable isotopes can be seen, with only 168Yb missing (this isotope has an abundance of 0.13%).

Similar results are found with the 399nm, with peaks from all of the isotopes present apart from 168Yb. This transition is stronger and so absorption can be more easily seen, whereas fluorescence gave a better signal for the 556nm transition.

Yb beam machine

A beam machine has been built as a source for Yb spectroscopy and locking of the green 556nm laser. The beam machine gives a large flux of Yb with which to get a signal of the relatively weak 556nm transition. The oven is heated by a nozzle heater, centred over some capillary tubes which act to collimate the atomic beam. The position of the heater relative to the Yb metal creates a large enough temperature gradient to ensure that the capillaries are always the hottest part and so won't become blocked. Further apertures (as can be seen in the middle picture) give more collimation and reduce the pressure in the rest of the apparatus.

The beam machine gives such a good flux that a circle of Yb has already appeared on the end viewport after only a couple of weeks of operation. This spot can be seen in the photograph below, along with one of the collimating apertures. The 556nm light is passed through the beam machine 5 times in order to increase the absorption signal seen, as the strength of this transition is relatively weak.

Vacuum system construction

The vacuum system was built over the course of a summer. The system was initially baked in two halves to allow us to get down to a lower final pressure. The oven end was done first, allowing us to test the Cs atomic beam to check that it was behaving as planned. The science chamber was then put into the oven before the whole system was assembled and baked for a final time in the lab itself. The final pressure was below 10-10torr, although this is limited by the resolution we can read from the ion pump currents.

The time lapse video was recorded over a period of 8 months and shows the construction and various stages of testing of the vacuum system.

Vacuum system design

The CsYb vacuum system design uses a dual species oven, which allows both species to be cooled using the same Zeeman slower. This means that more ports on the main chamber are available for the required MOT, DRSC and optical dipole trapping beams. The two 6-way crosses near the oven end will allow us to perform diagnostics on the atomic beams.

Both the science and oven ends are pumped with a 55l/s ion pump in conjunction with a NEG pump. An additional 40l/s ion pump will be used near the second 6-way cross. A differential pumping tube effectively separates the UHV science chamber from the higher pressure oven, hopefully allowing longer lifetimes for atoms trapped in the chamber.

The science chamber consists of 10 viewports which are coated for different wavelengths, as can be seen in the picture below. The top and bottom viewports will be recessed inside two re-entrant flanges. These will allow coils to be placed as close to the atoms as possible, enabling us to reach higher magnetic fields.

399nm laser design

A new design for the 399nm laser is being constructed and tested. The diodes we have need to be cooled to approximately -5°C in order to be the correct wavelength and this means that we need to ensure that there is no water vapour available to form ice around the diode. We hope to achieve this using only dessicant bags in a small cavity without the need to pump dry gas into the area. Both a slave laser and an ECDL have been designed (photographs below).

Updated by K. L. Butler, October 2013