Infrared Viewers improved

Third Infrared Window

Eyes of human beings can only see in short visible spectrum, thus limiting human vision physically in a very narrow spectrum of colors.

IR viewers can readily detect heat signatures. 

IR spectral windows

The heat detection often diminishes the information gathered and collected as an image by the IR cameras. 

InGaAs sensor can solve bunch of issues in imaging and surveillance in SWIR band.

The shortwave IR aka SWIR viewers however can get even better details about the image, providing better surveillance compared to other cameras in low light situations. InGaAs is remarkable material providing peak sensitivity in the SWIR band, from 900 to 1700 nm

SWIR camera in action

SWIR cameras can now be used to open the third and final window available for infrared photonics. Both Long wave (LWIR) and MWIR sensors can only sense a living being if his thermal signature is more than that of the surroundings. However SWIR uses reflected light, giving a window to look into yet with perks of visible light like imaging, 

Laser gated imaging: working principle

It is a technique that can be used for imaging through atmospheric obscurants such as smoke, haze, fog and dust. The technique employs laser pulses synchronized imaging sensor that illuminates object for duration as short as few nanoseconds to microseconds. The term gated is signified by the way sensor opens up for a short time, thus staying shielded off the scattered unwanted light. The camera gating time or exposure time will define the depth of view.

The two challenges for the technique are 

1. Imaging through atmospheric obscurants requires longer (IR) wavelengths, in order to reduce scattering on molecules and particles. 
2. High-power lasers in near-infrared (around 850 nm) are not eye-safe.

Lasers in the short-wave infrared (SWIR) range, &#955>1.4 μm, range, photons are absorbed in water within human eye’s surface before reaching its retina. Most eye-safe lasers operate around 1.55 μm, also the prime wavelength for telecomunication and laser range finders. Currently, most cameras operating in IR require cooling for optimal perfromance.

Sources:

1. SWIR photonics
2. Security and surveillance
3. why-swir
4. Laser Gated Imaging