Atoms surfing on light waves: A microlinear accelerator for neutral particles

The movie below shows the rapid acceleration of cold argon gases that were in the MOT. The argon atoms are trapped and accelerated by a light field produced by two laser beams that form a very rapidly accelerating conveyer belt. This captures the atoms and transports them up to high velocities. The conveyor belt is produced by two short pulses (140 ns duration) from an intense pulsed laser system that has been developed over the last few years in our lab. A rapidly changing frequency difference between the two beams allows the acceleration to occur over a 70 ns duration, taking them in our case to almost 200 m/s over a distance of approximately 10 microns. This is the realization of an optical microlinear accelerator for neutral particles. Although we demonstrate this fast acceleration on the cold argon atoms produced in our MOT, it is applicable to almost any atom or molecule. This is because we rely on the ability of the intense electric field to distort the charge cloud around the atom. This distortion results in the creation of a so-called electric dipole moment, which interacts with the optical field that created it. It produces a force that is large enough to trap the particles and rapidly accelerate them as shown below. The two red lines show the positions of the two acceleration beams that are turned-on for 140 billionth of a second. For the short acceleration period the atoms essentially surf on the optical wave just like surfers on ocean waves.

Temperature measurements

A movie of the expanding cloud with the new Andor camera gives a temperature of 73 microKelvin.

Yahoo! First MOT of metastable argon atoms

Today Peter and Conor saw their first ultra cold Ar* atoms in the magneto optical trap (MOT). We show two pictures of the glowing atoms trapped in the MOT. The first shows the cloud in the middle of the science chamber and second image is a close up. Next we plan to measure the density and temperature.

Simulation of sympathetic cooling

From the theory side of the project – view a simulation of sympathetic cooling of molecular hydrogen by argon atoms. The movie can be found here (http://www.youtube.com/watch?v=8NBPYOJ9l_0). Data for movie taken from direct simulation Monte Carlo calculations made by Paolo Barletta, our quantum scattering expert.

Progress in the lab…

Conor and Peter have been busy this week getting the RF discharge back up and running in the new vacuum system, in preparation for the first try at slowing atoms in the Zeeman slower. Some pictures of our work are shown below…

A view of the discharge looking at the skimmer from the science chamber

As above

A close-up of the above, inside the science chamber

As above with distant focus

The RF discharge at the source end of the vacuum system

The RF discharge inside the first vacuum chamber. The end of the glass tube can be clearly seen extending into the centre of the chamber

A view of the high-precision ion gauge at work inside the science chamber

Doppler-free saturated absorption spectra

Below is some data obtained using our extended cavity diode laser. We looked at absorption of the laser beam as it passed through the RF discharge cell as the laser was scanned in frequency over a few GHz. The small feature at the trough of the large background curve is centred at the transition frequency of the cooling transition we will use in our MOT. Its linewidth is roughly the natural linewidth of the cooling transition, which has been resolved using Doppler-free saturated absorption spectroscopy, to remove the effect of Doppler broadening in the metastable argon gas at room temperature. The ability to resolve this feature has enabled us to stabilise our laser to the frequency of the Doppler-free peak, using electronic feedback (more to come on the details of this method…).

Doppler-free saturated absorption spectroscopy on metastable argon

New vacuum system completed

A new vacuum system has been constructed. This will be used to produce our metastable argon MOT, and will also eventually house the QUEST. A separate connection flange on the side of the science chamber (wrapped in tin foil for baking!) will be used to bring molecules into the system for simultaneous trapping with the ground state argon atoms in the QUEST.

Vacuum system from the Ar source end

Side view of vacuum system

Peter and Conor survey their work!