Quantum Leap in Real-time Spectroscopy
Continuous monitoring of chemical products with an innovative matchbox-sized laser
Product quality monitoring is essential in pharmaceutical and chemical production, but often performed manually. Researchers from two Fraunhofer Institutes (Applied Solid State Physics in Freiburg and Photonics Microsystems in Dresden, Germany) may have found the ultimate solution. The team has developed a matchbox-sized laser module that can be rapidly tuned over a wide spectral range, opening the door to spectroscopic identification and quantification of chemical substances in real-time. Ralf Ostendorf, project manager at the institute in Freiburg, says the original goal was simply to develop a miniaturized laser source.
“Next, we decided to build a compact laser source with the aim of demonstrating the capability of laser-based mid infrared spectroscopy in different applications,” says Ostendorf. “We used a small silicon chip that integrates an optical diffraction grating in a micro-optical-electric mechanical system (MOEMS) scanner and combined this with a quantum cascade laser (QCL) chip. Both chips independently measure only a few millimetres – but the potential is enormous.”
QCLs emit light in a very broad spectral range in the mid infrared but the MOEMS diffraction grating can be continuously tilted (with frequencies of up to several kHz) using electrostatic forces, which in turn rapidly “tunes” the wavelength of the laser to a narrow band that can “scan” a wide spectral range. “At this point, we realized that we are able to perform very fast spectroscopy – even in real-time,” says Ostendorf.
Real-time spectroscopy allows continuous monitoring, which can be used to optimize chemical reactions or measure product composition. Moreover, Ostendorf says, “The spectral brightness of our laser also makes it possible to measure aqueous solutions. Traditional techniques like FTIR can only measure water film solutions up to 10 µm. We were able to identify caffeine dissolved in water (25 mg/L) through a 150 µm water film – and that’s very attractive for sensing solutions that are operated in a bypass flow cell.”
Ostendorf has high hopes for the device: “The system could be used for quality monitoring in the food industry, for the measurement of trace gases in environmental control, or even in the medical sector,” he says.
“We’re currently working on our first real-time spectroscopic measurements to demonstrate the capabilities. And we want to further miniaturize the laser source and simplify the alignment procedures of the grating and micro optics.”
Clearly, there is a great deal of work ahead, but widening the spectral tuning range could open up access to even more applications – at which point, the term quantum leap seems entirely justified.
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