Combat zones can be extremely chaotic. With a massive influx of sensory input, implementing clear communication, rugged tools, and reliable instrumentation is key to a successful mission. One of the most challenging tasks in any aerial combat situation is determining which assets on the ground to target and which ones to avoid. This determination is particularly challenging when enemy assets are camouflaged or hidden amongst civilian assets. Because of this challenge, a practice, commonly referred to as “painting the target,” was developed and has been successfully deployed for many years, allowing ground forces to identify and designate targets for successful engagement by aerial support. Of course, on the modern battlefield, soldiers aren’t marking targets with cans of spray paint for pilots to try to locate. Instead, they use portable laser designator systems, designed to illuminate the target with infrared radiation, easily detected and tracked by their aerial counterparts. In this application note, we will examine the critical laser requirements for laser designation systems and discuss what types of lasers are ideal for these systems.
There are many different types of laser designation systems used by the military today, as shown in the figure below (courtesy of Areté Associates). Still, they all share the same basic functionality and outcome. In a laser designation system, an infrared laser is fixed onto a target of interest and pulsed with a predetermined frequency code. This frequency code allows the infrared receiver on the plane or missile to efficiently recognize and lock onto the pulsed signal, scattered off the target, which enables the effective delivery of the projectile on target. At a glance, the laser requirements seem relatively straightforward. The laser needs to be invisible to the human eye, and it needs to have a programmable pulse rate. Still, when you look in more detail, many small factors add up to big problems if not appropriately addressed.
According to the NATO standard STANAG 3733, the laser beam divergence must be small enough that 90% of its energy is incident upon the target for 95% of the time, assuming a target size of 2.3m^2. Ideally, a soldier would be positioned at a safe distance (up to 5km away) from the designation target. Given this great distance, it is critical that the laser source has excellent beam divergence and pointing stability ratings. For example, if a laser beam has a half-angle divergence of 1 mrad, its radius will expand at a rate of 1 mm per meter. While this slight increase in radius may not seem like much, at a distance of 2km, an initial laser beam diameter of 1 mm will have expanded to 4 meters in diameter at the target. The figure below gives a visual representation of how rapidly a laser with a half-angle divergence of 1 mrad can balloon in size. This rapid divergence is problematic when locking onto smaller targets without more than 10% of the light missing the mark. Furthermore, it dramatically reduces the overall intensity of the reflected light, making it harder to be detected by the missile's targeting system. Similarly, problems can arise regarding the laser's pointing stability, given that any minuscule variations in beam angle at the source can result in massive variances of the beam's position at a distance. These significant variances in beam position can be devastating when trying to meet the 95% stability requirement also laid out in the NATO standards.
The accuracy of the pulse repetition rate is another critical property that one must consider. The infrared receiver on the plane or missile must confirm that the illuminated target matches the predetermined frequency code. Otherwise, the guidance system will not be able to lock on, regardless of the signal's brightness. Therefore, if there is jitter in the pulse triggering, the frequency and timing can be altered, distorting the frequency code and hindering the receiver's ability to confirm the signal. Lastly, in addition to the optical considerations laid out in the last paragraph, ruggedization, miniaturization, and power consumption requirements for the laser are equally important. Having reliable, rugged tools, built to withstand vibration and shock, and designed with low SWaP in mind - to be easily integrated with various equipment, where space and resource constraints limit your options - is key to mission success.
Areté Associates, based out of Northridge, California, set out to make the ideal source for laser designators, taking into account the full range of performance requirements laid out above, developing the AIRTRAC-LD laser source. This rugged 1064 nm DPSS laser source provides low divergence (< 250 mrad), high pulse energy (>70 mJ), and a programmable pulse repetition rate (up to 30Hz) with less than 1ns pulse jitter. All of these features combined make the AIRTRAC-LD fully compliant with NATO STANAG 3733, and therefore ideal for military deployment in laser designator systems. In addition to excelling at the optical requirements for laser designators, the AIRTRAC-LD also meets all MIL-SPEC requirements with a TRL7 rating, and is an ultra-compact, highly efficient, low SWaP laser source, weighing < 0.5 pounds, with a volume < 7 cubic inches, and a wall plug power consumption of < 30 W.
Here at RPMC lasers, we have teamed up with Areté Associates to introduce the AIRTRAC into the laser designation market. In addition to the AIRTRAC-LD, 1064nm variant described above, we at RPMC also offer the AIRTRAC-6M laser series in both the second (532nm) and third (355nm) harmonics. For additional information, including detailed technical specifications on these lasers, click here or talk to one of our knowledgeable Product Managers today by clicking the link below or calling us at 636.272.7227.