Laser-based gas analyzers are valued for their robustness, their real-time measurement capabilities, and their sensitivity. They provide unattended monitoring solutions for process analytics and environment.
Laser-based gas analyzers are however limited because of their narrow tunability: usually only light molecules can be measured, and one laser spectrometer will measure only one molecule.
Blue’s BTL technology unleashes the untapped potential of laser based gas analyzers:
- it measures hundreds of molecules including heavy compounds
- it measures traces of multiple molecules in real-time, all with a single source
- it dynamically identifies and eliminates unknown interference for specific measurement
Benefits of laser spectrometers are tied to their narrow tunability and high spectral resolution – so are their limitations
The common scientific principle is infrared spectrometry: each molecule has its unique infrared spectrum – or signature – which, when detected and selected from the signature of the other molecules, is used to quantify its concentration.
Compared to other light sources, lasers are very robust and stable, and offer spectral characteristics that enable a fast and sensitive measurement of molecules concentrations:
- focused power, that lights a couple wavenumbers only,
- high spectral resolution (<0.01 cm-1)
Specificity is achieved “by design”: laser spectrometers are traditionally built by taking into account the target molecule and the probable gas matrix in which the measurement needs to be performed: this enables to identify the peak of the target molecule where there is supposedly no interference. The laser source is then specified and integrated in the laser spectrometer.
The spectral characteristics of lasers however explain also the 2 limitations of laser spectrometers:
- laser’s narrow tunability enables to measure only light molecules, with absorption peaks that can be recognized over a couple of wavenumbers. It is typically difficult for a standard laser spectrometer to measure organic compounds with C>=3.
- laser’s narrow tunability enables to measure usually no more than one molecule. Another laser would be needed to measure another molecule.
What’s a Broadly Tunable Laser and how does it works?
Our Broadly Tunable Laser combines high resolution (<0.01cm-1 typical) with a wide spectral tunability. These 2 characteristics are not easily compatible. The wider the tunability, the harder it is to keep a good spectral resolution.
We achieve wide tunability by adding a small optical cavity to the laser. That optical cavity is an evolution of the OPO (Optical Parametric Oscillator) technology; it uses the properties of non-linear optics: from the source beam of the laser, the OPO cavity generates 2 output beams (called idler and signal). By changing in real-time some parameters of the OPO cavity, we are able to tune the output beam over a very wide spectral bandwidth (2×800 cm-1), while keeping the spectral characteristics of the laser (that is what’s difficult about this).
OPOs are usually limited to lab applications because they are – by nature – unstable optical cavities. A lot of our efforts were to develop (and patent) effective and robust controls to “tame the mustang” and make it a reproducible, repeatable device, that includes no moving parts.
The wavelengths are generated at will: a set of software-controlled instructions triggers routines in the OPO to generate the idler beam at the desired wavelengths, anywhere in the spectral range of the idler.
Schematically, the total idler bandwidth is divided into hundreds of contiguous spectral zones of a few wavenumbers, and each of these zones works like a single laser, that can be activated on demand to measure the target molecules. There is no limit in the number of such “Virtual Lasers” that can be activated for a measurement need.
- In order to measure heavy molecules, multiple contiguous Virtual Lasers are activated, providing enough bandwidth to target a recognizeable peak.
- Multiple Virtual Lasers are activated to measure multiple compounds.
- Probable interference can be avoided by design, but if unexpected interference happens, it can be measured and eliminated.
- Measurement routines can be combined, and can be adjusted at any time to adapt to changing conditions… It’s “just” software!
Interested to know more? Please contact us, we are happy to explain and share scientific articles about the technology. We also regularly speak at conferences.