Active CWA stand-off detection


We make people believe in stand-off detection again!

When you ask CBRN experts across the globe what they think about stand-off detection, a typical answer is: “I don’t believe in stand-off detection!” or “Stand-off detection doesn’t work!” Our company’s mission is to make people believe in it again. Under stand-off detection, we understand detection of even small quantities of an agent from a distance as great as 6 km – in a real environment.

Our R&D team has developed Falcon 4G – an active DIAL (differential absorption light detection and ranging (LIDAR)) stand-off detector that uses two tunable CO2 lasers.

The lasers enable Falcon 4G to detect, identify and also evaluate concentrations of chemical warfare agents (CWAs) at long range without the need of physical contact with the agents.



At the heart of Falcon 4G is a tunable CO2 laser with a wavelength of 9.6 µm-11.3 µm. The two lasers allow for:

  • Detection range of 6 km
  • Unmatched sensitivity

Stand-off detection relies on the absorption of infrared radiation by molecules of a gas. The key difference between active and passive stand-off detection systems is the utilization of an integrated source of infrared radiation for the active stand-off detection system.

Active and passive

The operation of a typical passive stand-off detection system can be explained as:

  • The background emits infrared radiation.
  • The emitted radiation passes through an agent, which causes partial absorption of the infrared radiation.
  • Infrared radiation that passes through the cloud is received by a passive stand-off detector.
  • Finally, the detector evaluates the received optical radiation.


A typical active stand-off detector is equipped with a dedicated source of infrared radiation and operates as follows:

  • The active stand-off detector emits short pulses of infrared radiation that pass through investigated volumes of air.
  • The transmitted infrared pulse is reflected of the background, pass through the cloud a second time, and finally, is received by the active stand-off detector.

Advantages of active stand-off

The key differences of active stand-off detectors compared with passive detectors are:

  • An integrated tunable source of infrared radiation (e.g. a CO2 laser)
  • Infrared radiation passes through the cloud twice – producing a stronger signature of the cloud on the received infrared radiation
  • The field of view of an active stand-off detector can be far smaller and results in a correspondingly higher effective range for the detection of heavy gases like CWAs
  • The possibility to eliminate influences of typical atmospheric constituencies, especially water vapours and CO2.

These differences result in better sensitivity and a bigger detection range for active stand-off detectors compared with passive stand-off detectors.


Eye safety

Because of used wavelengths, low pulse energies, and the large diameter of laser beams, the lasers utilized in Falcon 4G are eye safe. The infrared radiation emitted by the CO2 laser is absorbed by the eye’s vitreous humor (the clear jelly that fills the middle of the eye).

Elimination of influences of typical atmospheric constituencies

The tunable CO2 laser enables the Falcon 4G to select which wavelengths (laser lines) are utilized for the detection of CWAs. Falcon 4G does not use laser lines absorbed by water vapours; therefore, the negative impact of water in the atmosphere is negligible. Also, adverse effects of atmospheric CO2 can be minimized using the effective strategy of choosing detection laser lines.

Extra capabilities

Falcon 4G’s other capabilities through utilizing two pulsed tunable CO2 lasers are:

  • Detection of biological warfare agents (BWAs)
  • Evaluation of concentration profiles.

The usage of DISC (differential scattering) makes Falcon 4G capable of evaluating the particle size distribution of an aerosol. Keeping in mind that dangerous aerosols are approximately 5 µm in size, Falcon 4G can trigger an alarm in response to a potential BWA threat.

Falcon 4G is also capable of receiving back-scattered radiation from natural aerosols in the air such as water droplets, dust particles, and pollens. The reflected laser radiation enables a concertation profile of the CWA cloud along the measurement path to be evaluated.



We have tested Falcon 4G in various conditions and scenarios – urban areas, deserts, high-humidity environments and snow, and have hosted a number of end-users from several countries at our R&D facility to demonstrate its performance. Recently, TNO (the independent Organization for Applied Scientific Research in the Netherlands) visited our R&D facility to observe Falcon 4G in operation. TNO confirmed Falcon 4G had very good sensitivity and detection range using sulphur hexafluoride (SF6). The full report from this activity can be downloaded from our website.

groupWe have also invited a number of end users, mainly from Europe, for a demonstration of Falcon 4G. The weather conditions turned out to be challenging: snowing and cloudy. In these conditions Falcon 4G successfully detected SF6 in various concentrations, at a range of 4.6 km, and with SF6 releases as small as 150 g.


Active CWA stand-off detection offers new possibilities in detection, identification and evaluation of concentrations of agents from large distances. Falcon 4G has proven that the technology is ready for the market. Falcon 4G is capable to detect CWA vapours with sensitivities close to physical limits at large distances, due to the usage of tunable CO2 lasers. Our company’s mission is to make people believe in stand-off detection again. With Falcon 4G, SEC Technologies is one step closer to achieving this mission.