Optics and photonics

Room temperature maser operation enabled by nitrogen vacancy diamonds, by Laser Quantum

October 8, 2018

A critical break-through for masers has now made it possible for operation at room-temperature. The maser, a forerunner to the laser, emits microwaves instead of light, and could only previously be operated in temperatures close to absolute zero or within a vacuum. Now, with new research, masers can act continuously at room temperature.

The maser (microwave amplification by stimulated emission of radiation) was first invented in 1954, but due to its extreme cooling requirement never became as widespread as the laser. Previously, for a maser to function, it was required to be cooled to temperatures close to absolute zero (-273°C). However, due to the recent work undertaken by Dr. Jonathan Breeze and his colleagues at Imperial College London and University College London, they have developed a method to make masers act continuously at room temperature.

Masers have always been useful, specifically for measuring low or weak signals in astronomy and communicating with distant missions, however, they usually require cryogenic cooling to work. Masers amplify tiny traces of radiation with little noise, and in certain applications they can be more useful than lasers, as microwaves can pass through materials that optical light cannot.

In 2012, scientists had first demonstrated that masers could operate in room temperature. To achieve this, the group had used an organic molecule, pentacene. However, this only produced maser pulses lasting less than one thousandth of a second. Had this run continuously, they would have likely melted the crystal. Pentacene also degrades over time so was less stable as a gain medium.

To create a maser working at room temperature a nitrogen vacancy (NV) diamond was created; a synthetic diamond grown in a nitrogen-rich atmosphere. The diamond had carbon atoms ‘knocked-out’ and it was then heated, enabling nitrogen atoms and carbon vacancies to pair up.

Laser Quantum’s finesse pure 532 nm laser was used as an optical pump to excite the NV centres, one of the key requirements for the maser action. The finesse pure ensures long-term stability, with a noise level less than 0.02% RMS. Its excellent pointing stability of <2 μrad/°C makes it an ideal laser for pumping.

This break-through will enable masers to become more widely available for use and open new application areas. Masers are currently used as timekeepers in optical clocks and to boost radio signals from spacecraft, however, the list of applications is expected to grow and eventually become as widely used as the laser.

Some of the areas where masers could be seen to have a significant impact on the development of science and technology are medical imaging, airport security scanning, new technology for quantum computers, and potentially in a key role of improving sensors to remote-detect bombs. There is also scope for the maser technology to improve space communication methods and possibly find life on other planets.

Further developmental work is expected to continue for masers, but this initial demonstration is an exciting step towards their future

Read more about the finesse pure at www.laserquantum.com

The diamond containing nitrogen-vacancy (NV) defects centres, illuminated by the finesse pure 532-nm green laser. Credit: Jonathan Breeze, Imperial College London

Diamond held inside a sapphire ring and illuminated by Laser Quantum’s 532-nm green laser. The NV centres fluorescence red. Credit: Thomas Angus, Imperial College London