Resonantly tunable quantum cascade lasers (QCLs) are high-performance laser light sources for a wide range of spectroscopy applications in the mid-infrared (MIR) range. Their high brilliance enables minimal measurement times for more precise and efficient characterization processes and can be used, for example, in chemical and pharmaceutical industries, medicine or security technology. Until now, however, the production of QCL modules has been relatively complex and expensive.

The Fraunhofer Institute for Applied Solid State Physics IAF has therefore developed a semi-automated process that significantly simplifies the production of QCL modules with a MOEMS (micro-opto-electro-mechanical system) grating scanner in an external optical cavity (EC), making it more cost-efficient and attractive for industry. The MOEMS-EC-QCL technology was developed by Fraunhofer IAF in collaboration with the Fraunhofer Institute for Photonic Microsystems IPMS.

Inline measurements in industrial processes

“The market potential of MOEMS-EC-QCLs is enormous. The high brilliance in combination with spectral tunability due to the use of MOEMS diffraction gratings enables the further development of measurement methods based on FTIR spectroscopy and their use for inline measurement technology,” explains Dr. Marko Haertelt, leader of the Laser Measurement Technology Group at Fraunhofer IAF.

“We have now been able to bring the technology to an industry-ready level in terms of cost and availability: on the one hand, by placing the production of MOEMS-EC-QCL modules on a semi-automated manufacturing basis; on the other hand, by using a scalable approach to couple modules with complementary spectral ranges.

“The latter significantly reduces the number of different modules required to cover the entire MIR range from 4 to 11 µm, thereby achieving the necessary economies of scale,” emphasizes Haertelt.

Semi-automated production of quantum cascade lasers

The high manufacturing costs are the main obstacle to the widespread use of MOEMS-EC-QCLs: Until now, it was only possible to assemble the modules by hand because they had to be actively adjusted. The developed process automates the assembly process of MOEMS-EC-QCLs in essential parts with the help of a pick-and-place system, which significantly reduces manufacturing costs.

In addition, Fraunhofer IAF has developed a flexible and scalable method for efficiently combining multiple laser sources into a multi-core system. Individual QCL modules have only a limited spectral width. By combining modules with supplementary spectral ranges, application-specific multi-core systems can be configured that achieve effective spectral measurement speeds of more than 1 million wavenumbers per second.

Thanks to more efficient assembly and combination processes, the advantages of QCL technology are to be made widely available for the first time, particularly to small and medium-sized enterprises (SMEs).

Advantages and areas of application of MOEMS-EC-QCLs

MOEMS-EC-QCLs are characterized by broad spectral tunability in the mid-infrared wavelength range between 4 and 11 µm and high spectral brilliance. They are suitable for a wide range of spectroscopy methods (transmission, backscattering, ATR, microfluidic, point-of-interest spectroscopy) and allow complete infrared spectra to be recorded in just 1 ms.

The potential fields of application for MOEMS-EC-QCLs are correspondingly diverse: They can be used, for example, in semiconductor measurement technology to determine epitaxial layer thicknesses and their compositions, in process analytics to optimize chemical reactions, in process control to test coatings, in security technology to detect hazardous substances or intoxicants, and in the pharmaceutical industry for quality assurance.

To demonstrate the newly developed manufacturing and combination processes for MOEMS-EC-QCL modules, Fraunhofer IAF will be presenting a multi-core system comprising a total of four semi-automatically manufactured MOEMS-EC-QCL modules and associated peripherals at this year’s Laser World of Photonics in Munich from June 24 to 27. It will be exhibited together with other highlights from the optoelectronics business unit at the Fraunhofer joint booth in Hall A3, Booth 431.

The results were obtained as part of the AIRLAMet project (Electro-optical measuring system for inline production control in chip manufacturing). In this project, the partners Fraunhofer IAF, Fraunhofer IPMS, and Sacher Lasertechnik GmbH are working under the coordination of sentronics metrology GmbH on a device for measuring the thickness and composition of thin functional layers in semiconductor production. The provision of a high-performance and cost-effective laser light source for the measuring system marks a first milestone on the way to achieving the project objectives.