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Two weeks ago we published a blog post looking at time-of-flight (TOF) laser radar, now in this post, we are going to a look at what happens when you combine this technique with near-infrared (NIR) imaging in order to do active night vision imaging. In all TOF systems distance (or depth) is determined by the round-trip time it takes a laser pulse to travel to the target and back, but with the addition of a camera, this method can be used to produce a hypercube or “point cloud” containing a three-dimensional image of the target. While theoretically this can be done using short pulsed lasers of any wavelength, it is generally preferable to work in the near infrared, and 1.5 microns in particular because it is simultaneously eye safe and invisible.
In order to understand why 1.5 microns is considered to be an eye-safe wavelength, we must first take a look at the absorption properties of water which has a rather high absorption coefficient around 1.5 microns as shown in the plot below. As a result, the liquid inside of the human eye sufficiently absorbs and diffuses the laser light before it is able to damage the retina, making this wavelength ideal for field applications.
While in theory this approach can be utilized for generating time-gated images under any lighting conditions, the most common application of this technique is in night vision surveillance systems. The image below is an example of one such active night vision system which was taken using a q-switched Er:Glass laser at 1540 nm with 10mJ pulse energy and an InGaAs time-gated camera.
At RPMC Lasers we offer a wide variety of q-switched Er:Glass lasers from Optitask which are ideally suited for both active night vision systems and more traditional laser rangefinders. These lasers are available with both diode pumped and flashlamp pumped excitation depending on your pulse energy requirements, and are also available with both active and passive q-switching. This allows you to choose pulse energies between 2mJ and 10mJ, pulse widths from 9ns to 40ns, and pulse repletion rates from 1Hz to 30Hz.
For detailed technical specifications on our Er:Glass lasers click here or talk to one of our laser experts today by calling 1-636-272-7227.