Fundamentals, Fun and Funding
I’ve been lucky enough to spend time in the grey area between analytical spectroscopy and atomic physics. It’s fascinating and enlightening – but is it chemistry?
Working with lasers – the major tool of spectroscopy research for the last 40 years – I have become very well acquainted with the dangers of being swallowed up by the fascinating subject of atomic physics. But I am a chemist! Getting the balance wrong can have a negative impact on funding if you’re unlucky. For example, it’s difficult to get funding for research on the coherent interaction of atoms with radiation fields if you’re an analytical spectroscopist... they’ll tell you it’s not chemistry. And they’re right – in a way.
Atomic physics is clearly at the root of understanding spectroscopy. Take the diode laser. If you want to do the perfect atomic absorption spectroscopy experiment, you can take a diode laser with an extremely narrow frequency and tune it to the center of an atomic absorption profile of an atom trapped by laser cooling. At that point, only natural broadening is occurring, and guess what: you no longer need to be concerned with the absorption oscillator strength... Suddenly, the language of atomic physics starts to take over.
While having fun with spectroscopy, the ability of lasers to manipulate atoms and molecules has fascinated me most of all, even if it is actually in the realm of atomic physics. It’s quite comical that BEC here stands for Bose–Einstein condensate rather than ‘background equivalent concentration’ as it should for an analytical spectroscopist. But perhaps we should not be too quick to pigeonhole academic interests. Let’s consider single atom detection and single molecule detection – those advances come from excellent work done by atomic physicists but also by atomic and analytical spectroscopists, such as James Winefordner.
I for one am certainly very pleased to have an atomic physicist as a colleague; Ove Axner has been following the impressive work in noise-immune cavity-enhanced optical heterodyne molecular spectroscopy (NICE-OHMS) done at the Joint Institute for Laboratory Astrophysics in Colorado. From the theory, one can calculate the signal-to-noise ratio and find that NICE-OHMS is capable of detecting less than one atom – theoretically, of course. With that kind of sensitivity, it’s hard to imagine all of the amazing possibilities. Unfortunately, as an analytical chemist you need a practical application. There is a dichotomy at work here. As said by many analytical spectroscopists, it’s difficult to develop a fantastic method if it’s not driven by an application. But on the other hand, the application would have to be extremely demanding and important to develop such a sensitive method. Sometimes, predicting where the future might lead – or where we should focus our efforts – can be almost impossible.
The NICE-OHMS example clearly highlights the strong connection between analytical spectroscopy and atomic physics, especially with regards to noise. After all, there is no signal without noise. To fully understand spectroscopic noise, you quickly enter the territory of stochastic variables, signal communication theory, and so on. At first, it can appear that such discussions are outside the scope of analytical spectroscopy, but actually, understanding the fundamentals and characterizing noise is at the very root of improving the quality of our measurements.
Only if we know the characteristics of noise can we devise instrumentation that is capable of improving the signal-to-noise ratio, decreasing the limit of detection, and increasing analytical sensitivity. In other words, we can only improve if we understand. Unfortunately, I don’t think we have enough people working on problems with this philosophy in mind. On a more elementary level, I certainly focus on signals and noise, and how they relate to measurement in my spectroscopy classes. After all, there is no algorithm or chemometric program that is capable of superseding a good understanding of data quality, which can only come from fundamental knowledge. For the same reason, I believe that it is very important for students (and academics!) to invest heavily in learning what has been done before. I am absolutely convinced of the need to not only look at papers that have been published in the last four years, but rather the last forty.
It’s true that the grey (and yet extremely exciting) border between physics and chemistry can have difficulty attracting funding these days – especially for an analytical spectroscopist – but that doesn’t make it in any way trivial. I feel lucky to have been given the freedom to explore so many different facets of my field – and I worry that the current generation will not be so fortunate.
