2024-02-27 10:43:43
The DragonFirea British laser program[1] of power, made the headlines a few weeks ago[2]. What does this laser bring new compared to the many equivalent programs existing in the world? Absolutely nothing, except that he beats them all when it comes to communication. It has been more than ten years since the first power lasers were tested. The United States, Israel, China, Russia, France, Germany, India… already have, at least in testing, such weapons whose power varies from a few kilowatts for the least powerful, to 300 kilowatts for the laser High Energy Laser Scaling Initiative the Lockheed Martin.
It must be said that laser weapons present, at least on paper, some interesting advantages:
– the cost of each shot is ridiculously low, equivalent to the value of a rifle bullet, or barely higher;
– the high directivity of a laser allows very precise shots, de facto limiting the risks of collateral damage and allowing great selectivity of targets;
– with a laser, there is no need to ensure ammunition supplies, logistics are limited to energy production. As long as this is available, there is no risk of running out of ammunition;
Ÿ it is possible to modulate the power of the laser according to the desired effects, the engagement distance or the environment;
Ÿ power lasers allow for very varied application cases and are not specific to a particular type of target.
The futuristic side of these weapons, which refers to science fiction, would tend to make people think that they are ultimate and unstoppable equipment. However, if we know their limits and their constraints well, it is possible to find countermeasures allowing, not to completely ward off a laser, but to attenuate its effects.
Physical limits and constraints of lasers
The principle of operation of laser weapons is quite simple. A concentrated beam of light strikes a surface. This causes heating which causes, after a more or less long time depending on the material and the power of the laser, a melting or combustion of the material which ends up being pierced.
A laser beam, to maintain its power density as much as possible (number of watts per cm²) over the distance, must diverge as little as possible, which requires particularly rigorous aiming of the beam. We are talking about less than a centimeter per 1,000 m. This level of pointing precision therefore requires having, beforehand and at a minimum, the position of the target in elevation and azimuth, with extreme accuracy. However, there are relatively few sensors capable of providing such a level of measurement. This involves using several complementary devices. For example, the position given by a radar is then refined by a LiDAR[3] ; but we can also use a high-resolution optical system (the level of precision will be determined by the number of pixels of the camera). Of course, we then understand that the effective firing range will depend on the distance over which the sensors can maintain the required level of precision, depending on the size of the target: the requirement will not be the same if it is involves hitting a drone or an aircraft with a wingspan of several tens of meters. Therefore, the larger the target, the more it can be struck by a laser located at a great distance.
This requirement for precision also requires very high stabilization responsiveness of the laser pointer. The effects of wind, vibrations or any other movement must be compensated with great care throughout the time the target is pointed, which itself can move. This makes this type of system particularly difficult to use on a mobile platform (vehicle, ship, aircraft), requiring very sophisticated pointing and stabilization devices. Even on a large target, the laser beam must always aim at the same location to create sufficient heating and be effective.
A very important point is also the ability of the laser system to compensate for the effects of refraction of the beam which, depending on the passage through air layers of different temperatures and hygrometry, will then no longer have a rectilinear trajectory. The greater the distance between the source and the target, the more significant the phenomenon is likely to be.
Of course, a laser also remains vulnerable to aerological and weather conditions. In order to limit these effects, most power lasers use SWIR band wavelengths (Short Wave Infra Red) which is less sensitive to these effects. In fact, the wavelength used is often around 1064 nm. However, rain can render a laser completely ineffective as the level of diffraction can be significant.
Let us not forget, even if it seems logical, that laser firing requires maintaining intervisibility with its objective, unlike a missile which, depending on its guidance mode, can be autonomous in pursuing the target, even if it -it hid from the shooter (“fire and forget” mode).
Finally, the firing rate of a laser is also conditioned by the power emitted: of all the energy supplied, the beam uses no more than 50%; the rest is dissipated in the form of heat; therefore, the more powerful a laser, the greater the cooling requirements. Consequently, the more powerful a laser is, the more likely it is that its firing rate and illumination time will be low.
What countermeasures against lasers?
This question does not yet arise but, from the moment this type of weapon becomes widespread, whether in ground/air defense or against ships or vehicles, it will become crucial. However, when we study the constraints and limits of this technology, it is possible to determine at least four areas of work to develop countermeasures.
– The first axis is the simplest and most obvious. This involves jamming the radar responsible for detecting and acquiring the target. As with any other weapon system, preventing this step is guarding against attack. This solution is only accessible to large platforms such as weapons planes or combat ships which have a suite of countermeasures. This also means that existing systems can already offer protection against high-power lasers.
– The second axis consists of playing on the albedo, that is to say the reflective power of the material. There are paints (with titanium oxide for example) offering very good albedo and resisting heat well without significantly weighing down the wearer. Likewise, there are polymers and ceramics with excellent light reflection and temperature resistance properties. This makes it possible to return a significant part of the light energy and therefore to limit the heating generated. In this way, it is possible to delay the “cliff” effect, the moment when the material loses its reflective properties under the effect of heat, and to make its destruction much longer. This approach limits the effects of the laser and allows either to delay destruction sufficiently so that the targeted object (shells, rockets, missiles or drones) reaches its goal, or, in the case of an aircraft or vehicle, to allow him to escape. Delaying the effects also prevents the laser from being able to deal with other threats during this time, making saturation attacks all the more effective.
– The third axis can be combined with the previous one. This involves varying the exposures of the target so that it is not the same place that is pointed, thus allowing its surface to cool. This can take several forms: autorotation for shells, rockets or certain missiles, erratic trajectory with change of direction for drones or aircraft, for example.
– The fourth and final axis proposes using smoke bombs generating opaque carbon clouds around the intended target. These will have the effect of absorbing and deflecting a very large part of the laser energy. These types of smoke bombs already exist and are used by the Russian navy to mask its ships, those equipped with a laser detector Spektr-F (Half Cup), a laser beam designation. They are launched from the decoy launchers (PK-2, PK-10 and PK-16) of the ship and allow it to be hidden in its entirety. Of course, this equipment is only suitable for slow platforms that are large enough to allow their transport, such as ships, land vehicles, but also helicopters which could pull this type of smoke behind them in a maneuver away from the laser. In the naval field, it would also be possible, by watering, to create diffraction of the beam causing it to lose all effectiveness.
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Laser weapons have a certain number of advantages which explain why they are gradually arriving in arsenals; their entry into service should not take long in certain countries like Israel, for example, for the fight against drones. As their power increases, so will their range of potential targets. However, lasers are not without certain defects or certain limitations, which mean that they will probably not replace cannons or missiles but will complement them.
Lasers aren’t invincible either; As these weapons come into use, countermeasures will naturally be put in place. Ultimately, laser weapons will be part of the equipment of armies, alongside existing weapons and will find their place as one effector among others.
[1] English acronym Light Amplification by Stimulated Emission of Radiation (amplification of light by stimulated emission of radiation). It has now become a common name.
[3] English acronym Laser Imaging Detection and Ranging (laser detection and distance estimation), is a distance measurement technique based on the analysis of the properties of a beam of light returned to its emitter.
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