Short-wave infrared (SWIR)

Short-wave infrared, SWIR, sits in the electromagnetic spectrum just beyond visible light and before the mid- and long-wave infrared bands — roughly 0.9 to 1.7 micrometres by the common industrial convention, extended to about 2.5 micrometres on extended-range InGaAs detectors. Objects at very high temperature — a welding arc, a molten weld pool, a furnace interior — radiate strongly enough in this band that a SWIR sensor, filtered to a narrow slice of it, can image them directly, where a sensor built for ambient-temperature work would either saturate or need heavy optical attenuation to survive the arc’s brightness.

That property is why SWIR and long-wave infrared are not interchangeable choices for the same job, even though arc glare itself is largely invisible in the LWIR band. A LWIR sensor is built to resolve small temperature differences near ambient and moderately elevated temperatures — the heat-affected zone, an interpass surface, a cooling bead — on an uncooled microbolometer that saturates at the top of its calibrated range and responds too slowly to freeze a fast transient. A SWIR sensor is built the other way: tuned to the intensity range of the arc and the pool themselves, with a cooled photon detector fast enough to freeze droplet transfer, it images geometry, spatter and pool boundary detail that a LWIR camera pointed at the same scene cannot resolve, because its resolution and response are built for the ambient range, not the pool.

Sensor material is the practical reason the two bands cannot be served by one camera fitted with a different filter. LWIR detectors are typically uncooled microbolometers; SWIR detectors use a different photodiode material entirely, with different cost, sensitivity and cooling requirements. A welding cell that needs both weld-pool visualization and heat-affected-zone monitoring generally carries two distinct camera types rather than one camera doing both jobs, which is also why infrared camera as a category covers instruments that are not interchangeable with each other.

Weld-pool and process cameras that work in or near the SWIR band belong to the broader welding camera product category, distinct from the ambient-band thermal cameras used for surrounding-zone monitoring described under thermography.