Atomic clocks are no longer based on a microwave transition in cesium, instead operating with other atoms that are excited using optical frequencies. Some of these new clocks are portable. At its QUEST Institute, PTB is currently developing a transportable optical aluminum clock in order to measure physical phenomena outside a laboratory. A prerequisite for this is that the required lasers are able to endure transportation to other locations. PTB physicists have therefore developed a frequency-doubling unit that will continue to operate when it has been shaken at three times the Earth’s gravitational acceleration. The results have been published in the current issue of the Review of Scientific Instruments.