High Speed Infrared 4k cams

Recent developments in cooled mercury cadmium telluride (MCT or HgCdTe) infrared detector technology have made possible the development of high end infrared 4k cams for use within a wide selection of demanding thermal imaging applications. These infrared cameras are available nowadays with spectral sensitivity in the shortwave, mid-wave and long-wave spectral bands or alternatively in two bands. In addition, a number of camera resolutions can be found consequently of mid-size and large-size detector arrays and various pixel sizes. Also, camera features now include high frame rate imaging, adjustable exposure time and event triggering enabling the capture of temporal thermal events. Sophisticated processing algorithms can be found that result in an extended dynamic range to prevent saturation and optimize sensitivity. These infrared cameras may be calibrated so that the output digital values match object temperatures. Non-uniformity correction algorithms are included that are independent of exposure time. These performance capabilities and camera features enable a wide variety of thermal imaging applications that have been previously not possible.

At the heart of the high speed infrared camera is really a cooled MCT detector that gives extraordinary sensitivity and versatility for viewing high speed thermal events.

1. Infrared Spectral Sensitivity Bands

Because of the accessibility to a number of MCT detectors, high speed infrared cameras have been designed to use in many distinct spectral bands. The spectral band may be manipulated by varying the alloy composition of the HgCdTe and the detector set-point temperature. The effect is really a single band infrared detector with extraordinary quantum efficiency (typically above 70%) and high signal-to-noise ratio in a position to detect extremely small quantities of infrared signal. Single-band MCT detectors typically fall in among the five nominal spectral bands shown:

• Short-wave infrared (SWIR) cameras - visible to 2.5 micron

• Broad-band infrared (BBIR) cameras - 1.5-5 micron

• Mid-wave infrared (MWIR) cameras - 3-5 micron

• Long-wave infrared (LWIR) cameras - 7-10 micron response

• Very Long Wave (VLWIR) cameras - 7-12 micron response

In addition to cameras that utilize "monospectral" infrared detectors which have a spectral response in one band, new systems are being developed that utilize infrared detectors which have a reply in two bands (known as "two color" or dual band). Examples include cameras having a MWIR/LWIR response covering both 3-5 micron and 7-11 micron, or alternatively certain SWIR and MWIR bands, as well as two MW sub-bands.

There are certainly a selection of reasons motivating the choice of the spectral band for an infrared camera. For several applications, the spectral radiance or reflectance of the objects under observation is what determines the very best spectral band. These applications include spectroscopy, laser beam viewing, detection and alignment, target signature analysis, phenomenology, cold-object imaging and surveillance in a marine environment.

Additionally, a spectral band may be selected due to the dynamic range concerns. This extended dynamic range would not be possible with an infrared camera imaging in the MWIR spectral range. The wide dynamic range performance of the LWIR system is easily explained by comparing the flux in the LWIR band with this in the MWIR band. As calculated from Planck's curve, the distribution of flux as a result of objects at widely varying temperatures is smaller in the LWIR band compared to MWIR band when observing a scene having exactly the same object temperature range. In other words, the LWIR infrared camera can image and measure ambient temperature objects with high sensitivity and resolution and at once extremely hot objects (i.e. >2000K). Imaging wide temperature ranges with an MWIR system could have significant challenges as the signal from high temperature objects will have to be drastically attenuated leading to poor sensitivity for imaging at background temperatures.