Room Temperature Continuous-Wave Inorganic Maser

Until very recently the MASER could only be used in very specialist applications such as radio astronomy. The reason for this is that cryogenic cooling and to a lesser extent, high applied magnetic fields, prohibited mass production on the grounds of both complexity and cost. Despite the fact that the MASER was discovered before the LASER these issues meant that the latter, which does not need applied magnetic fields or cooling, saw widespread adoption in a huge range of applications from bar-code readers, laser discs to laser eye surgery.

In 2013 Imperial and UCL were awarded an EPSRC funded research project to produce a room temperature MASER. Although we had preliminary observations that room temperature masing was possible we had not verified this in a different laboratory setting, nor did we have a clear idea of how the masing molecule interacted with light and which crystal orientations or dopant concentrations would be optimal. This collaboration was remarkably successful achieving all the objectives we set.
Now, in what is another world first, the team has constructed a diamond MASER capable of continuous-wave operation at room temperature.

Our previous research has concentrated solely on organic materials as the masing medium. In this proposal we will explore the potential of masing in inorganic materials at room temperature. In doing so we will obviate two key problems encountered with organics.

Problem 1 - Decay rates: The primary obstacle that prevents continuous operation in organics is the relatively long lifetime of the lowest triplet sub-level, reducing the number of pentacenes available for optical pumping (bottleneck) and destroying the population inversion.

Problem 2 - Heating: The organic gain medium, pentacene in p-terphenyl we first used to demonstrate a room temperature MASER cannot withstand a continuous illumination by a laser because the temperature of the terphenyl host rises above its melting point.


Solution to both problems: a radical but exciting departure which will address both problems simultaneously is to explore high spin states in inorganic materials with high melting/decomposition temperature and favourable thermal conductivities (T.C.): such as diamond (M.P. 3550C; T.C. 2000 W/mK) and silicon carbide (2730C; T.C. 120 W/mK).
Very recently we observed masing at room temperature in diamond exploiting NV centres. This means we can build upon a huge wealth of research in the UK and elsewhere on diamond NV centres. Again there is much research exploring defects in SiC that we can build on. We have initiated a collaboration with the group of Prof. Dr. Vladimir Dyakonov at Würzburg group who are currently exploring SiC. REF. https://arxiv.org/pdf/1709.00052.pdf

Achieving this would further establish without doubt the UK as the key place to carry out fundamental research on the topic of room temperature MASERs.

Who will benefit from this research?

1) There are two demonstrators that we will build to take advantage of the maser's unique properties.
- The most likely early take-up will probably be in very low noise amplifiers and measurements of phase noise. Currently, the noise floor of the best HEMTs is around 22 K at measured 17 K (Bryerton et al DOI:10.1109/MWSYM.2009.5165788). However at room temperature the noise floor of the best InP HEMTS is 0.82dB (60K) (Tsu et al Microelectronic Engineering (2010) doi:10.1016/j.mee.2010.02.012). Estimates of the noise floor of our maser device indicate that it could be very competitive and show that there is plenty of incentive to explore the area of low noise amplifiers.
- Associated with applications that demand a low noise floor are devices that benefit from very low phase noise. We have plans to build two devices so that we can measure the phase noise.
2) Magnetic Resonance Imaging / Nuclear Magnetic Resonance and Electron Paramagnetic Resonance - all three would benefit from better LNAs.
3) Flowing on from its potential as an extremely sensitive sensor one can imagine miniaturisation to devices capable of medical diagnostics. Indeed the current LCR) inductance, capacitance, resistance) circuit is only a millimetre in size.
4) Quantum computing. Given that the fundamental process occurring in a maser is the conversion of optical photons to coherent microwave photons, we expect the field of diamond-based quantum optics to be an immediate beneficiary of this work, where the optical-microwave photon interface is key to the initialization, manipulation and detection of quantum states.

A caveat must be noted. It took us 5 years to move from a pulsed MASER to a continuous-wave MASER and the average time taken from discovery to serious commercialisation is anywhere between 10-30 years. In preparation however, IC and UCL are taking care to protect intellectual property with one patent granted, and four filed. The protection of intellectual property is being handled by Imperial Innovations and by UCL Enterprise. We already have collaboration agreements in place.

How will they benefit from the research?
It is really too early to make definitive statements as to where the research will lead and who will benefit, but to generalise:

- the maser is expected to impact in the area of healthcare because of improved signal to noise sensors for magnetic resonance in particular.
- In the area of communications again because of improved signal to noise ratio and because of potential for very low phase noise. In the proposal we will explore the phase noise of the system.
- possibly in the area of room temperature quantum computing although this has some way to go.

We will take advice from an Industrial Partner board which will be made up from our industrial partners as well as Imperial Innovations, UCL enterprise and the principal investigators. The main objective of the board will be to focus on the impact of the research by taking a broader and more commercial view of the science and engineering. As mentioned in the case for support we will target low noise amplifiers and very low phase noise as the initial demonstrators.