A gated imaging system is built up around a Focal Plane Array (FPA) of detectors where the Read-Out Integrated Circuit (ROIC) is able to read out time-domain information about the incident light in each pixel, while a radiometric imager integrates the incident light over a certain time period. Gated imaging and time resolved imaging opens up several new opportunities.

 

Gated imaging gives a better contrast in cloudy environments. With gated imaging the exposure time of the camera is tightly controlled so that only light from a certain distance is collected on the image sensor. Light stemming from objects at other distances is not imaged. Thus, should a cloud or other scattering object be in-between the camera and the object, the time resolved camera will be able to reduce the disturbance in the image from these objects. Gated imaging is commonly used together with a pulsed laser to provide active illumination of the object. In gated imaging, we use the knowledge of the distance to the object to achieve better contrast by adapting the expose time of the time resolved camera.

 

In three dimensional imaging, the analyzed signal from the camera is used to measure the distance of the object in each pixel. This enables us to make a 3-dimensional image.

 

In some applications, one wants to image the light emerging from an object under high background conditions. This is a common problem in thermography of active objects, tomography, vibration analysis and ellipsometry, for instance. A time resolved camera can act as an imager with a lock-in amplifier in each pixel, thus canceling out the signal not in sync with a certain frequency.

 

The possibilities enabled by time-resolved imaging are very significant and the field has been a very active topic in academia for about 10 years. However, real-life applications have been scarce for a very specific reason. Most of the applications require active illumination with a laser light with power in the range of several Watt and the developed devices have been intended for visible light. Since visible laser light of the intensities required is damaging eyes already for intensities as small as 1 mW, most applications in the visible wavelength range will be confined to laboratories and operated by scientists.

 

This problem is solved by using active illumination operating in the short-wavelength-infrared (SWIR) wavelength range. This wavelength range is well suited for active illuminations for two reasons:

Eye-safety: The wavelength region is completely eye-safe due to the absorption of light by the water in your eye.

Manufacturability: For the technology to work, both powerful light sources and fast detectors are available.