GoPhotonics interviewed Søren M. M. Friis, PhD, the Head of Sales and Business Development at NLIR. He is responsible for driving the commercial development of NLIR’s mid-infrared spectroscopy technology, with a focus on identifying and scaling high-value applications in both research and industry. He holds a PhD in nonlinear optics from the Technical University of Denmark (DTU), where his work focused on all-optical signal conversion and amplification in optical fibers.

At NLIR, Søren works closely with customers to translate technical capabilities into practical measurement setups. His work focuses on application development, customer support during evaluation and implementation, and close dialogue with users, with a strong emphasis on bringing mid-infrared spectroscopy into real-world production environments.

Q. Could you start by introducing NLIR, when was the company founded, and what does it specialize in?

Søren M. M. Friis: NLIR was founded in 2013 as a spin-out from the Technical University of Denmark. The company is built on a patented technology that enables frequency upconversion of mid-infrared light into the visible and near-infrared range, where high-performance silicon detectors can be used. This approach allows mid-infrared signals to be detected with significantly higher speed, sensitivity, and lower noise compared to conventional technologies.

Today, NLIR designs and manufactures mid-infrared spectrometers and light sources for research, industrial, and defense applications. The spectrometers operate in the 2.0 - 5.0 µm spectral range, where many molecules, including water, carbon dioxide, and hydrocarbons exhibit strong fundamental absorption features.

NLIR’s spectrometers have no moving parts and are designed for use directly in industrial environments. Combined with the performance of CMOS line-array detectors, this enables fast, sensitive, and robust measurements. The result is a platform well-suited for real-time quality control and process monitoring.

Q. What exactly is mid-infrared technology, and what inspired NLIR to focus on this field?

Søren M. M. Friis: Mid-infrared light in the 2.0 - 5.0 µm range covers the strongest absorption bands of many fundamental molecular vibrations, enabling highly specific and sensitive chemical identification. Unlike near-infrared techniques, which rely on weaker overtones and often require complex modeling, mid-infrared spectroscopy allows for more direct and quantitative analysis of gases, vapors, and condensed-phase materials.

Despite this advantage, traditional mid-IR instruments such as FTIR spectrometers are typically too slow, sensitive to environmental conditions, and confined to laboratory use. As a result, many industries still rely on periodic off-line measurements rather than continuous monitoring.

NLIR chose to focus on this spectral region because it represents a clear gap in the sensor market. By leveraging its upconversion technology, NLIR enables fast, sensitive, and robust mid-IR spectroscopy in a compact, field-deployable format. This makes it possible to perform real-time, multi-component measurements directly in industrial processes, replacing intermittent lab-based analysis with continuous, in-line insight.

Q. Could you give us an overview of NLIR’s product portfolio? Which product segment currently represents your largest market?

Søren M. M. Friis: NLIR’s core product portfolio consists of fiber-coupled mid-infrared spectrometers covering the 2.0 - 5.0 µm wavelength range. These instruments are designed to integrate easily into existing setups and are conceptually similar to conventional grating spectrometers used in the visible range but optimized for mid-infrared performance and industrial use.

In addition, NLIR offers thermal light sources, optical accessories, and interface solutions that simplify system integration, including sample illumination and efficient light collection.

In addition to spectrometers, NLIR also provides its core upconversion technology as a stand-alone device – Wavelength Converter. This solution is primarily used in research applications, where there is a need for ultra-fast or low-light mid-infrared detection.

In terms of market segments, industrial applications currently represent the largest share of demand. This is driven by the need for fast, robust, and real-time measurements in process monitoring and quality control.

Q. Which industries or applications are currently driving the strongest demand for NLIR’s mid-infrared solutions?

Søren M. M. Friis: NLIR’s technology is applied across both industrial and research environments, but current demand is primarily driven by applications that require fast and robust measurements under real operating conditions. One key application is monitoring the transmission of engineered optical coatings. During production, NLIR’s spectrometers enable real-time measurements inside coating systems, allowing process optimization and improved quality control.

Another important area is black plastic sorting. By measuring mid-IR reflection spectra, different polymer types can be identified, even when conventional visible or near-infrared methods fail.

A third growing application is surface coating analysis, where NLIR systems are used to measure thickness, composition, and coverage through reflection-based measurements, often directly on production lines.

Across these applications, the common requirement is the ability to perform fast, reliable, and continuous measurements in industrial environments. This is where NLIR’s combination of speed, robustness, and sensitivity provides a clear advantage.

Q. Could you share some interesting or emerging applications of mid-infrared spectroscopy?

Søren M. M. Friis: NLIR’s primary focus is on enabling mid-infrared measurements in well-established environments where conventional technologies like FTIR fall short. Our goal is to bring mid-infrared analysis out of the laboratory and into production environments, where speed, robustness, and real-time measurement capabilities are required.

Q. How can the production of optical coatings be monitored in real time using the MIDWAVE NLIR spectrometer?

Søren M. M. Friis: Optical coatings are produced by vapor deposition inside a vacuum chamber, where thin layers of material are deposited onto a substrate with high precision. The final optical performance depends critically on the thickness and sequence of these layers.

The MIDWAVE Spectrometer can be integrated directly into the coating system to monitor the process in real time. For infrared coatings, it measures the evolving transmission or reflection spectrum during deposition, providing a direct readout of the optical performance. This enables operators to track whether the coating is developing according to specification and to stop the process at the optimal point.

Because the measurement is fast and continuous, the system supports real-time process control, improving yield and ensuring consistent coating performance.

Q. Software plays an important role in all NLIR products. Could you tell us more about the NLIzeR software, which products it supports and the key features it offers?

Søren M. M. Friis: NLIR provides a simple and user-friendly software interface, NLIzeR, for operating its spectrometers and collecting spectral data. The software is designed for straightforward setup and reliable data acquisition, both in laboratory and industrial environments.

In addition, NLIR offers an easy-to-use SDK that allows customers to integrate the spectrometers directly into their own systems. This enables full control over data acquisition and supports seamless implementation in automated setups or existing process infrastructure.

The focus is on making the hardware easy to operate and integrate, rather than relying on complex software layers.

Q. How does NLIR’s upconversion technology enhance real-time detection of multiple gases in dynamic industrial or environmental settings?

Søren M. M. Friis: NLIR’s upconversion technology enables real-time detection of multiple gases by combining broadband mid-infrared spectroscopy with high-speed detection. In a typical setup, infrared light is transmitted through a gas stream, and the spectrometer measures how different wavelengths are absorbed. Because many gases have distinct absorption features in the 2.0 - 5.0 µm range, this allows simultaneous identification of multiple species within a single measurement.

The high acquisition speed makes it possible to follow rapidly changing gas compositions in real time. This is particularly valuable in dynamic environments such as industrial processes, combustion systems, or emissions monitoring, where conditions can change on very short timescales.

Unlike conventional gas sensors that typically target one or two species at a time, NLIR’s approach provides continuous, multi-component analysis from a single measurement. This enables more complete insight and faster response in applications where gas composition is critical. As illustrated in NLIR’s multi-gas monitoring applications, the technology supports live tracking of gases such as CO₂, CH₄, NOₓ, and H₂O directly in process streams, without the need for sequential measurements or multiple sensors.

Q. Who are NLIR’s typical customers — what types of companies or laboratories use your systems, and where are they based?

Søren M. M. Friis: NLIR works with a mix of industrial companies, system integrators, and research institutions. On the industrial side, customers are typically companies involved in manufacturing processes where real-time chemical or material insight is valuable, such as coatings, plastics, and process industries. In research, our systems are used in universities and specialized laboratories working with mid-infrared spectroscopy and advanced sensing.

We generally operate globally, with customers across Europe, North America, and Asia.

Due to the nature of our collaborations, we are not able to share specific customer names, but the common denominator is large manufacturing or production units with a need for fast, robust, and application-specific mid-infrared measurements.

Q. How does NLIR support its customers in integrating your systems into existing processes to ensure ease of use and reliable performance?

Søren M. M. Friis: NLIR focuses on providing strong technical guidance during the evaluation and onboarding phases. We work closely with customers in the early stages to ensure the system is well understood and correctly implemented.

Our spectrometers are designed to be easy to set up and operate, and most customers can get started quickly. During initial integration, we support typical tasks such as system setup, basic communication, and first measurements.

If customers encounter challenges, we are available to assist with specific technical questions related to the instrument and its integration.

For more advanced or application-specific support, we offer additional assistance on an hourly basis. In most cases, however, customers are able to work independently once the system is up and running, as the product is a well-defined measurement instrument rather than a complete analytical solution.

Q. Looking ahead, where do you see NLIR in the next three years within the mid-infrared spectroscopy landscape, and what are your main goals for growth and innovation?

Søren M. M. Friis: NLIR’s ambition is to become a leading supplier of high-performance mid-infrared spectroscopy solutions, with a particular focus on speed, compactness, and real-world usability.

Today, our systems are already used in both research and industrial environments, including real-time monitoring applications. Building on this foundation, our primary focus over the coming years is to expand our presence in industrial settings, where spectroscopy can be integrated directly into production processes. NLIR wants to bring mid-infrared analysis into production environments.

A key part of this development is making our systems even easier to use, while improving sensitivity and measurement precision. Equally important is strengthening how our technology interfaces with real processes. In many applications, the interface between the spectrometer and the measurement environment is just as critical as the instrument itself.

As we work across different industries, we continuously build application knowledge and experience. Each measurement case presents its own challenges, and expanding our ability to support these is central to our growth.

Overall, the goal is to provide highly capable, easy-to-integrate measurement instruments, combined with the expected application expertise needed to ensure they can be used effectively in real-world conditions.

About NLIR

NLIR (Non-Linear-Infrared) is revolutionizing mid-infrared light detection with its innovative spectrometers that offer rapid spectral acquisition in milliseconds, exceptional sensitivity, and high resolution. Its sensors are based upon a novel upconversion technology, converting MIR light to NIR light. This enables the use of uncooled silicon-based sensors for detection of mid-infrared light, lifting many challenges of the conventional Fourier-Transform InfraRed (FTIR) spectrometry methods and opening new MIR measurement opportunities.

NLIR's mission is to advance optical sensing solutions, helping industries overcome challenges and pioneer future innovations. Its products cater to research groups in public institutes, private companies, and production departments needing in-line, on-line, or at-line MIR spectroscopy across diverse sectors, including but not limited to optics manufacturing, laser characterization, gas analysis, material inspection, and others.