Sensing and Spectroscopy
The optical frequency comb is a Nobel Prize winning innovation in laser technology that is poised to revolutionise spectroscopy. We use this massively parallel laser source to characterise atomic and molecular samples with unprecedented precision, accuracy, and speed.
We also specialise in precision laser absorption and two-photon spectroscopy, both within conventional cells and fibre based architectures, with applications in fundamental physics, frequency standard development and quantum computing.
Optical Breath Analysis
The exhaled breath is a rich source of information about the inner life of the human body - but untangling this complicated molecular mixture into a quantitative measurement of its constituent components is currently an unsolved problem. We are developing a new instrument that leverages the Nobel Prize winning technology of the optical frequency comb to enable analysis of such mixtures.
The optical frequency is essentially a massively parallel laser source with millions of individual laser signals equally spaced across the optical spectrum. By combining a frequency comb source with an innovative parallel detector and a highly sensitive sampling system, we can generate a real-time spectral signature of the sample. Computational techniques developed by the radio astronomy community will then be used to extract concentrations of individual molecular components at the parts-per-billion level.
Real-Time Contaminant Monitoring in Liquid Natural Gas Processing
Solid formation in key liquid natural gas processing steps costs an estimated $500 million in lost production annually. Characterising the concentration of heavy hydrocarbons (which act as nucleation sites) is key to avoiding costly shutdowns whilst operating at economically viable temperatures.
We are developing an instrument for real-time analysis of the concentration of these heavy hydrocarbons based on massively parallel absorption spectroscopy using an optical frequency comb.
Spectroscopic Determination of the Boltzmann Constant
The International System of Units (SI) system is an extremely successful coherent framework for describing the physical world. At its heart are seven base units, from which all others are derived. It is highly desirable to link these base units to fundamental constants, rather than man made artefacts. It is also desirable to have a systematic, easily replicable determination process for realising these units anywhere in the world. This project is aimed at fulfilling these ideals for the Kelvin, the base unit for temperature, by linking it to the Boltzmann constant and developing a determination process based on atomic caesium gas.
Atomic gases in thermal equilibrium exhibit the well-known Maxwell-Boltzmann velocity distribution. When interrogated at a suitable transition by a sufficiently pure laser source, the width of the resulting Doppler-broadened lineshape is related to the true, thermodynamic temperature of the caesium gas. If an independent measurement of temperature is available, then this system can also measure the Boltzmann constant.
Our current system is capable of a Boltzmann constant determination with 6ppm precision and uncertainty of 71ppm, primarily limited by the purity of the laser source.
Narrow-Band Parallel Absorption Spectroscopy
We are developing the technology to utilise the optical frequency combs as an interrogation source for high-precision narrowband absorption spectroscopy of caesium. By modifying the effective repetition rate of the comb, we can make an interrogation source of with very closely spaced optical frequencies, which is perfect for sampling the narrow hyperfine features of a caesium vapour. Novel RF acquisition techniques allow the entire lineshape to be measured in real time - removing the need for a scanned laser source.
Whispering Gallery Resonators for Precision Thermometry
The Whispering Gallery in St Paul's Cathedral, London, famously allows visitors to talk to each other across the vast expanse of the dome by exploiting multiple reflections of acoustic waves from the curved inner wall. Our whispering gallery resonators exploit an analogous phenomenon in which total internal reflection around the curved, highly polished edge of a crystalline disc leads to extremely high quality factor resonances for laser light. By using two lasers separated by nearly an octave in optical frequency, each locked to a resonant mode, we can build a device that is effectively immune to thermal expansion effects and resolve extremely small fluctuations in temperature (via the thermo-optic effect) at the level of 30nK. This has produced the most sensitive measurement of temperature ever recorded! (link to press release) Such a device can find application in biology and medicine, for calorimetry of biological interactions. With slight modification it could also be used as a force, humidity or pressure sensor - as well as a platform for measuring small levels of contaminants or chemicals in the environment.
High Precision Atomic Magnetometry
Detection of small deviations in magnetic field is extremely useful in many applications, including: medical, for detection of fluctuating magnetic fields in the heart or brain; defence, for passive detection of submarines and geology, for geomagnetic surveys. We are developing small, all optical, atomic magnetometers based on the Non-linear Magneto-Optical Rotation (NMOR) technique. By using an appropriately tuned and modulated laser it is possible to sample the Larmor frequency of a collection of atoms, which, in turn, is determined by the local magnetic field. These magnetometers have demonstrated sensitivity at the picoTesla level, which compares very well with current technologies. In addition, these sensors can be easily miniaturised and fibre coupled, making it an extremely convenient platform for application in the field.