Mid-IR Spectrometers and Detectors

All mid-IR spectrometers and detectors from NLIR are based on sum-frequency generation (SFG). These products use SFG in a process called upconversion, which aims to change the wavelength of incoming mid-infrared (MIR) light to near-visible light. Nonlinear optical processes are generally driven by high-intensity electrical fields inside media that exhibit large nonlinear coefficients and small losses, for example, LiNbO 3 crystals. For upconversion, in which three electrical fields participate, one of these fields must be of sufficiently high intensity. Although upconversion has been known for many years, the need for a high-intensity laser field has made it either too expensive or too inefficient for commercialization.

NLIR mid-IR spectrometers and detectors contain years of development and expertise, and have achieved exceptional properties in terms of noise, speed, sensitivity, and reliability that makes them unique in the Mid-IR market.


The requirements for upconversion, which limit the achievable efficiency and bandwidth, inherently filter out thermal noise from the surroundings. The only noise in the detectable bandwidth that co-propagates with the signal is upconverted and makes it to detection. The rest of the thermal noise from the surroundings that would be detected by a conventional mid-IR detector is simply not upconverted. Similarly, a conventional mid-IR detector also has a significant amount of internal noise because of its own temperature, which is the reason why many mid-IR detectors are cryo-cooled. This noise contribution is also largely avoided after upconversion because hardly any thermally emitted photons exist at the upconverted wavelengths at room temperature.


A high-power laser and the desired optical bandwidth determine the efficiency of the upconversion process. Higher power and a narrower bandwidth give higher efficiency. For a wide bandwidth of 2.0 – 5.0 μm, the conversion efficiency is approx. 0.001. Combined with an appropriate near-visible light detector, that still outperforms a standard mid-IR detector alternative in terms of noise-equivalent power for many applications. If a narrower bandwidth is desired, for example, 3.3 – 5.0 μm, the conversion efficiency is> 0.01, and for a bandwidth of only 50 nm around 3.0 µm, the conversion efficiency is> 0.1. 

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