The set-up is sealed to be gas-tight to the outside in order to protect the crystal, which is highly sensitive even to the slightest contaminations. The QUEST Institute has developed a design for this so-called frequency-doubling cavity, which is based on a monolithic – and therefore highly stable – frame onto which all mirrors and the crystal are mounted. Due to the dichroic coating of the mirror, it passes out of the resonator and is then used for reading the clock. A non-linear crystal placed in this ring transforms the circulating light into light of half the wavelength. Instead, a long-wave infrared laser must be frequency-doubled twice in succession.ĭuring this process, the light is coupled into a closed ring of four mirrors so that a high optical power is circulating within the ring. For this wavelength, it is not possible to simply buy a laser diode. This clock requires, among other things, two UV lasers operating at 267 nm. This last problem concerns in particular the transportable aluminum clock that is being developed at the QUEST Institute. They must painstakingly be readjusted – which leads to a loss of valuable research time. This is why optical structures that have worked perfectly well in the laboratory may initially be unusable at the destination. Furthermore, significant physical shocks may occur during transportation. The ambient temperature, for example, is much less stable. Their operation outside a protected laboratory environment, however, poses many challenges. PTB is currently developing several different types of atomic clocks that can each be transported in a trailer or in a container. One of the prerequisites for this is that the optical frequencies of the two clocks can be compared e.g. This so-called “chronometric levelling” represents an important application of clocks in geodesy. What initially sounds like a bizarre idea has quite practical effects and banefits: Two optical atomic clocks having an extremely small relative measurement uncertainty of 10 -18 can measure the difference in height between arbitrary points on the Earth at an accuracy of just one centimeter. It was Einstein who discovered that two clocks that are located at two different positions in the gravitational field of the Earth will tick at different speeds. The results have been published in Review of Scientific Instruments. PTB physicists have therefore developed a frequency-doubling unit that will even continue to operate when it has been shaken at three times the Earth's gravitational acceleration. A prerequisite for this is that the required lasers can cope with transportation to other locations. In a significant step forward, some of these new designs of clock can even be transported to other locations.Īt its QUEST Institute, PTB is currently developing a portable optical aluminum clock that is designed to measure physical phenomena such as the red shift, as predicted by Einstein, outside the laboratory. These clocks are no longer based on a microwave transition in cesium, but they instead operate with other atoms that are excited using optical frequencies. At the same time, PTB is already developing various atomic clocks of the next generation. For this purpose, it runs some of the best cesium atomic clocks in the world. Good to go: Set up of the optical atomic clock developed at PTB's QUEST Institute.German research center Physikalisch-Technische Bundesanstalt (PTB), Based in Braunschweig, is well known for providing accurate time, such as for radio-controlled clocks.
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