The Physikalisch-Technische Bundesanstalt (PTB) has developed a frequency-doubling unit for transportable lasers
The Physikalisch-Technische Bundesanstalt (PTB) is known for providing time e.g. for radio-controlled clocks. For this purpose, it operates some of the best cesium atomic clocks in the world. At the same time, PTB is already developing various atomic clocks of the next generation.
These clocks are no longer based on a microwave transition in cesium, but they rather operate with other atoms that are excited using optical frequencies. Some of these new clocks can even be transported to other locations. At its QUEST Institute, PTB is currently developing a transportable optical aluminum clock in order to measure physical phenomena (such as the red shift that was predicted by Einstein) 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 even 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.
It was Einstein who found out that two clocks that are located at two different positions in the gravitational field of the Earth tick at different speeds. What initially sounds like a bizarre idea has quite practical effects: 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.
This so-called "chronometric levelling" represents an important application of clocks in geodesy. One of the prerequisites for this is that the optical frequencies of the two clocks can be compared e.g. via glass fibers.
PTB is currently developing several different types of atomic clocks that can each be transported in a trailer or in a container. Their operation outside a protected laboratory, however, involves many challenges: The ambient temperature, for example, is much less stable. Furthermore, significant shocks may occur during transportation. This is why optical structures that have worked perfectly well in the laboratory may initially be unusable at the destination. They must painstakingly be readjusted - which leads to a loss of valuable research time.
This last-mentioned problem concerns in particular the transportable aluminum clock that is being developed at the QUEST Institute. This clock requires, among other things, two UV lasers at 267 nm. For this wavelength, it is not possible to simply buy a laser diode. Instead, a long-wave infrared laser must be frequency-doubled twice in succession. During this process, the light is coupled into a closed ring of four mirrors so that a high optical power is circulating within the ring.
A non-linear crystal placed in this ring transforms the circulating light into light of half the wavelength. Due to the dichroic coating of the mirror, it passes out of the resonator and is then used for reading the clock. 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. 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 developers of the cavity were able to demonstrate on a prototype that it also doubles the laser light while it is exposed to accelerations of 1 g. Furthermoe, it was shown that the frequency doubling efficiency is not impaired after being subjected to accelerations of up to 3 g for 30 minutes. This corresponds to five times the value stated in Standard ISO 13355:2016 about road transportation on trucks. The cavity is, however, not only mechanically robust, but it is just as efficient as comparable systems that have been developed by research groups of other institutes. Moreover, 130 hours of uninterrupted continuous operation was demonstrated.
In view of these properties, the QUEST Institute has made several of these doubling cavities for different wavelengths (not only for UV) which became integral components of various quantum-optical experiments, with the aim of providing these experiments reliably with laser light. Moreover, a German optomechanics company has licensed the design in order to use it as a basis for a commercial product. This project was supported by the Deutsche Forschungsgesellschaft (grant CRC 1128 geo-Q, Project A03, CRC 1227 DQ-mat, Projects B03 and B05) and the Leibniz-Gemeinschaft (SAW-2013-FBH-3).
Prof. Dr. Piet O. Schmidt, QUEST, phone: +49 (0)531 592-4700, e-mail: email@example.com
S. Hannig, J. Mielke, J. Fenske, M. Misera, N. Beef, C. Ospelkaus, P.O. Schmidt: A highly stable monolithic enhancement cavity for second harmonic generation in the ultraviolet. Review of Scientific Instruments 89, 013106 (2018)
A "Scilight" of the publication was published by AIP ("A robust frequency doubling cavity makes a transportable laser source for use in a UV optical clock"): http://scitation.
Piet O. Schmidt | EurekAlert!
New type of low-energy nanolaser that shines in all directions
18.12.2018 | Eindhoven University of Technology
NASA research reveals Saturn is losing its rings at 'worst-case-scenario' rate
18.12.2018 | NASA/Goddard Space Flight Center
Researchers from the University of Basel have reported a new method that allows the physical state of just a few atoms or molecules within a network to be controlled. It is based on the spontaneous self-organization of molecules into extensive networks with pores about one nanometer in size. In the journal ‘small’, the physicists reported on their investigations, which could be of particular importance for the development of new storage devices.
Around the world, researchers are attempting to shrink data storage devices to achieve as large a storage capacity in as small a space as possible. In almost...
The more objects we make "smart," from watches to entire buildings, the greater the need for these devices to store and retrieve massive amounts of data quickly without consuming too much power.
Millions of new memory cells could be part of a computer chip and provide that speed and energy savings, thanks to the discovery of a previously unobserved...
What if, instead of turning up the thermostat, you could warm up with high-tech, flexible patches sewn into your clothes - while significantly reducing your...
A widely used diabetes medication combined with an antihypertensive drug specifically inhibits tumor growth – this was discovered by researchers from the University of Basel’s Biozentrum two years ago. In a follow-up study, recently published in “Cell Reports”, the scientists report that this drug cocktail induces cancer cell death by switching off their energy supply.
The widely used anti-diabetes drug metformin not only reduces blood sugar but also has an anti-cancer effect. However, the metformin dose commonly used in the...
A research team from the University of Zurich has developed a new drone that can retract its propeller arms in flight and make itself small to fit through narrow gaps and holes. This is particularly useful when searching for victims of natural disasters.
Inspecting a damaged building after an earthquake or during a fire is exactly the kind of job that human rescuers would like drones to do for them. A flying...
12.12.2018 | Event News
10.12.2018 | Event News
06.12.2018 | Event News
18.12.2018 | Materials Sciences
18.12.2018 | Physics and Astronomy
18.12.2018 | Physics and Astronomy