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NLIR, a pioneer in mid-infrared (MIR) spectroscopy solutions, is setting new benchmarks with its unique upconversion-based detection technology. By converting challenging mid-infrared (MIR) wavelengths into the visible and near-infrared range using sum-frequency generation in nonlinear crystals, NLIR eliminates the need for cryogenic cooling and complex MIR detectors. This innovation makes MIR sensing faster, more sensitive, and more accessible for a wide range of applications.

NLIR’s technology represents a fundamental shift in how mid-infrared (MIR) light is detected and measured. Traditional MIR detection relies on specialized detectors that are often bulky, expensive, and require cryogenic cooling. MIR wavelengths are particularly susceptible to thermal noise, and the detectors themselves generate significant internal noise due to their operating temperature. NLIR takes a very different approach, rooted in advanced nonlinear optics, which eliminates many of these limitations.

At the heart of NLIR’s innovation is sum-frequency generation (SFG), a process that mixes mid-infrared light with a high-power laser inside a nonlinear crystal. When these beams interact, they generate a new photon whose energy equals the sum of the two originals. This photon falls within the near-visible spectrum, which can be easily detected with common technologies like CMOS sensors or silicon photodetectors. To make the process efficient, NLIR developed a method to introduce a 1064 nm laser into a nonlinear crystal, such as lithium niobate. This design allows mid-infrared light to enter from one side while the upconverted light exits from another, minimizing absorption and intensity loss. This setup makes the technology compact and efficient, avoiding the complexity of older MIR systems.

One of the remarkable features of this upconversion technique is its resistance to noise. Conventional MIR detectors capture substantial thermal radiation from the environment. NLIR’s method is selective; it only converts light that matches specific energy criteria, effectively filtering out much of the environmental noise. Furthermore, since the upconverted light is in the near-visible range, it doesn't suffer from the same thermal noise problems that plague traditional detectors. The result is a much cleaner, more accurate signal.

However, two parasitic processes take place inside the crystal during upconversion. Firstly, the crystal itself emits random photons due to its temperature. The photons emitted in the same direction as the signal are upconverted and added to the detection as noise. This noise dominates above 3.0 μm and grows with wavelength. Secondly, photons from the high-power laser decay through spontaneous downconversion, another nonlinear process. When these photons are upconverted, they are detected as noise. This latter process is referred to in the literature as upconverted spontaneous parametric down-conversion (USPDC) noise, and it dominates at wavelengths below 3.0 μm.

The two new sources of noise introduced in the upconversion scheme are significant enough to be observed in the 2.0 – 5.0 μm Spectrometers at sampling frequencies <0.1 Hz. In the Single-Wavelength Detectors, the contribution varies depending on wavelength and bandwidth, but its effect is always included in the specifications.

Speed is another advantage of NLIR’s approach. Although the upconversion interaction is complex, it occurs almost instantaneously. The nonlinear crystal responds extremely rapidly to the light fields, so any delay is practically negligible for measurement purposes. Only in very high-frequency scenarios, such as above 100 GHz, does the interaction speed become a limiting factor, and even then, the effect is minimal.

Upconversion efficiency depends on the applied laser power and the width of the wavelength range being measured. Narrow ranges of MIR light can be converted with high efficiency, allowing very precise and sensitive measurements. When broader wavelength bands are needed, the efficiency drops, but not so much that it prevents practical use. In fact, even at lower efficiencies, NLIR’s detectors can still produce valuable data, especially when paired with powerful signal processing and modern software. NLIR has also made this advanced technology accessible. Their devices are designed to be easy to use, simply connect the hardware, run the software, and you can begin taking mid-infrared measurements in real time. The output is high-resolution, high-speed, and remarkably clean, making it ideal for demanding applications in research, industry, and environmental monitoring.

NLIR has redefined what’s possible in mid-infrared spectroscopy. By turning an elaborate scientific concept into a practical detection system, they’ve opened new frontiers for fast, low-noise, room-temperature MIR sensing. Their upconversion technology combines precision, simplicity, and scalability, bridging a long-standing gap between high-performance optics and real-world usability.