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TDLAS: Laser Absorption Spectroscopy for Quality Controls
TDLAS: Laser Absorption Spectroscopy for Quality Controls

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09 December 2020

TDLAS: Laser Absorption Spectroscopy for Quality Controls

It is possible to know and monitor in a very effective and inexpensive way what happens to the product in terms of maintaining the organoleptic characteristics

Laser absorption spectroscopy, and by this we mean TDLAS (Tunable Diode Laser Absorption Spectroscopy), is an optical measurement technique for measuring the presence of certain gases. To do this, it uses a specific physical property that certain molecules in the gaseous state have, which allows them to absorb light.


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Specifically, some molecules can absorb light only at specific bands, namely for specific and defined wavelengths. The highly monochromatic, tunable emissive characteristics of new solid-state lasers allow this property to be exploited in order to measure gas presence in an extremely accurate way, and to measure partial and total pressure inside partially transparent, closed containers and various types of containers made of different materials, in different colours and with varying thickness and optical characteristics.

Antares Vision TDLAS (Tunable Diode Laser Absorption Spectroscopy)

We talk about it with Paolo Tondello, Application Specialist Gas Sensing and Leak Detection of FT System. 

What parameters can be measured? Can it be applied to in-line quality control?

With TDLAS technology, the concentration of a certain gas in a closed container can be measured, as well as the partial pressure of this gas and the total pressure caused by all the gases. The measurement can be selected depending on the specific gas to be measured. As it is an optical measurement, it is non-invasive, non-destructive and there is no need to prepare the sample to be measured in a certain way. Thanks to these properties, laboratory instruments can be created, with which the concentration parameters of a gas in the headspace of the container can be measured non-destructively and even repeatedly over time on the same sample. In this way, it is possible to find out and monitor – in a very effective and inexpensive way – what happens to the product when it comes to maintaining its organoleptic characteristics, fermentation and, more generally, its quality. We have developed applications for the bottling industry, with instruments designed for carbonated products, vacuum-packed products, or products with added nitrogen, as well as MAP monitoring applications for the food packaging industry. Since it is non-destructive, this technology can be applied in-line to measure 100% of production to check seals, preventing possible leakage from trays or flowpacks containing MAP-packaged products. It also allows for process control by monitoring the pressure and headspace filling of products in the pharmaceutical, bottling and food packaging industries.


In what way has laser spectroscopy revolutionised the way quality control is performed in various fields? Would you like to share some of the successful examples with us?

TDLAS has revolutionary features compared to conventional inspection methods based on contact between gas and sensor. The fact that it is optical, and therefore a non-contact technology, has made it possible to perform in-line checks on 100% of the samples that are now able to go beyond destructive sampling checks, which are very expensive, and especially, with much lower statistical effectiveness than checks performed on the entire production. Here are some examples of successful applications that have significantly improved production quality and efficiency:

  1. When bottling, liquid nitrogen is dosed in drops to pressurise the bottle, which makes it possible to reduce the amount of plastic used. Measuring pressure in-line, after 100% of the bottles have been capped, offers numerous advantages, including the certainty of not having any deflated containers or containers with leaking caps when palletising them. In addition, the nitrogen dosing process can also be monitored, and feedback can be sent to the dosing system itself, with considerable reductions in nitrogen consumption.
  2. In the food packaging industry, specifically MAP-packaged products, both trays and flowpacks, checking for leaks on 100% of production ensures that only compliant products are placed on the market. In fact, if the products are non-compliant, mould could form over time due to the presence of micro-holes in the sealing, causing problems in terms of quality and brand reputation. Since 100% of production is controlled, the manufacturer can monitor the packaging and sealing process and avoid rejects being produced due to a malfunction of the packaging machine.
  3. In the case of classic method sparkling wine, our technology has allowed producers to monitor 100% of the bottles at the end of the second fermentation process, before uncorking them for the disgorging process. In this way, the highest quality bottles can be selected over those in which refermentation caused some problems. As a result, product quality can be guaranteed and monitored, and the part of production where some problems occurred is not wasted either, which means that the product can be reworked and recovered.


How did the idea of applying laser spectroscopy to quality control come about? 

TDLAS technology has been well known for many decades, but was only used in laboratories until the 2000s when the ground-breaking advancements in laser technology made by the telecommunication industry finally provided reliable, relatively inexpensive lasers suitable for the purpose of TDLAS. The team of researchers, who later founded the spin-off L pro that initiated these developments, was busy measuring CO2 inside closed containers when, one day, the CO2 cylinder that they had used to create the samples ran out. At that point, initially just for fun, they tried to measure the only product in the laboratory that was sure to contain large amounts of CO2: a bottle of Prosecco. The discovery that thick, dark containers such as wine bottles could also be measured paved the way for the many applications that came later.


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