Pyrometry Detectors

This stacked semiconductor architecture acts as its own natural optical filter. Incoming thermal radiation first strikes the top standard InGaAs photodiode, which absorbs shorter-wavelength photons—typically up to a 1.7 µm cutoff—and converts them into an electrical signal. Because semiconductors are transparent to wavelengths longer than their bandgap cutoff, longer infrared waves pass cleanly through the top detector with minimal loss. Directly underneath, an extended-wavelength InGaAs detector captures these transmitted photons (typically 1.7 µm to 2.2 µm) and generates a second independent signal. The pyrometer’s electronics then divide the two signals, using the predictable shift in energy ratio across wavelengths to calculate an exact surface temperature.

For demanding industrial and scientific environments, this vertical design delivers critical performance advantages. Because smoke, dirty viewing windows, and shifting material emissivity reduce radiation across both bands equally, the ratio remains constant and the temperature reading stays accurate without frequent recalibration. Furthermore, ratio detection accurately measures targets smaller than the optical spot size—such as thin wires or molten metal streams—while vertical stacking eliminates the parallax errors common in side-by-side sensors. Ideal for metallurgy, semiconductor processing, glass manufacturing, and high-temperature furnaces, InGaAs sandwich photodiodes provide dependable thermal monitoring where traditional sensors fail.