Diffraction

In this activity we propose some useful ways to develop knowledge and understanding of the theory and
practical applications of diffraction gratings. Moreover, by linking diffraction gratings with the cuttingedge work of the Quantum Technology Hubs, we aim at inspiring students to consider a career in quantum
technology development. Students will be able to see that despite the inaccessibility of quantum physics often
perceived by people, these concepts are not far removed from the students’ current academic experience.
The Grating Magneto Optical Traps (GMOTs) developed at the University of Strathclyde (Glasgow), in
partnership with Kelvin Nanotechnologies, are an interesting step forward in achieving ‘laser cooling’ in more
efficient ways. This will potentially lead to miniaturization of laser cooling technology, and hence of quantum
sensors in general. In ‘laser cooling’ a minimum of four laser beams are focused on a relatively small number of
atoms from different directions. The frequency of the lasers used is such that the photons’ momentum will be
transferred to the atoms trapped. As the laser beams hit the atoms from four (or six) directions, the atoms will
slow down and almost completely stop vibrating. We call these ‘cold atoms’ because the temperatures reached
in these optical atom traps are in the order of the pK.
The grating triplet at the base of the GMOT shown in the figure below enables the trap to use a single laser
beam, split and steer it to the centre of the trap, where atoms can be slowed down to temperatures of
3μK. This removes the need to have multiple laser beams and/or mirrors, potentially reducing the time and
complexity needed for calibration. For more information on how laser cooling is achieved see our ‘Laser Cooling’ activity.