Staying hidden: Countering laser-based optic detection

By Jackson White, Head of Commercial at Sentinel Photonics

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Lasers are an integral reality of modern warfare. From rangefinding and target designation for long-range targeting, lasers are influencing how militaries combat, manoeuvre and stay ahead.

Recognising this shift, UK Chancellor Rachel Reeves recently earmarked a £2.2 billion uplift in defence spending. Within that, laser technologies were cited as critical to the UK's defence future, including greater investment in the Royal Navy's DragonFire directed energy weapon capability.

But while laser development has focused heavily on offensive power, adversaries are also exploiting them in more subtle - and often more insidious - ways. One growing concern is the use of lasers to locate covert operators via their optics. This threat has evolved rapidly in recent years, and traditional camouflage and concealment are no longer sufficient to stay hidden.

Retroreflection: The hidden giveaway

The science behind the threat is simple but deadly effective. Most optics - from rifle scopes, night vision goggles and thermal cameras - rely on precision glass elements that channel light to the user's eye. But an invisible laser pulse can illuminate these optics, and that non-visible light is bounced back in the exact direction it came from - this is retroreflection.

Retroflection, or the “cat's eye effect”, is what makes road signs and reflective clothing visible at night. In the field, it has lethal consequences. Any adversary scanning an area with a non-visible laser will instantly spot a returning flash from an optic, revealing not just a general presence, but an exact location.

It's a modern form of backscatter - the non-visible light betrays the operator. And it does so with clarity and precision, regardless of how well they are concealed in other spectrums.

What makes retroreflection especially problematic is its consistency and predictability. Light enters the optic, reflects off the reticle or internal surfaces, and is returned with minimal loss. It's a reliable and repeatable detection method that works at speed, at distances often beyond the effective range of the weapon they are attached to, and in low-light conditions.

In extreme cases, adversaries can use retroflection to send a harmful laser back to the optic. Dubbed “the eyeball popper”, this has been used to cause irreversible damage to the retina of the eyeball looking through the optic. Equally, once an optic's location has been identified adversaries can deploy targeted munitions to the area such as artillery or mortar strikes.

The battlefield cost of being seen

Laser detection is particularly devastating because it offers passive targeting - an adversary can identify and plot the location of optics without emitting any RF or visible signal that might alert the user. By the time the operator realises they've been seen, it may already be too late.

Despite this risk, most NATO and allied optics currently in service lack robust protection. Some have laser filters, but these are often tuned for a narrow band of known wavelengths and can be defeated by modern variable-wavelength (multispectral) laser systems.

Addressing the vulnerability

This is one of the key operational gaps that Sentinel Photonic aims to address. Developed in the UK by former DSTL scientists, its FROST solution is a field-ready, passive protection system that eliminates retroreflection without compromising optical performance.

FROST - short for Filter for Retroreflection and Optic Signature Treatment - is a signature management device designed to be mounted on the front of common optics. It neutralises the cat's eye effect by preventing incoming laser light from being reflected straight back to the source.

FROST filters, which can be retrofitted to a wide range of optics using standard mounting threads or custom mounting masks, provide laser protection and counter-surveillance capabilities, and ensure operators remain undetectable in the face of advanced laser systems.

The FROST system is designed to be used without the need for additional power, software, or calibration, therefore minimising the SwaP burden to the soldier, making it ideal for dismounted troops or low-signature operations. It is also effective against both detection and visual damage, protection level dependent, reducing the risk of eye injury, or worse, from high-powered laser systems.

In rigorous trials across the globe, FROST has never been defeated by a tested laser system. That includes emerging threats from China and Russia, which use dynamic wavelength selection to bypass traditional optical filters.

Lessons from the field

In a recent end user evaluation, Sentinel was invited to test a newly acquired batch of optics believed to be protected. Using a threat-representative laser pulse, the Sentinel team identified the location of each optic in less than 10 seconds.

Operators were unaware they were being observed - and had no means of detecting the laser. In an operational environment, these optics would have acted like beacons, compromising both the mission and the lives of those using them.

FROST-equipped versions of the same optics were then tested under identical conditions. No retroreflection was detected, and the operators remained hidden throughout the exercise.

LasINT: The new discipline in EW

FROST has been designed using real-world, measured, laser threat data and performance verified against a range of battlespace laser threat systems - this is known as laser intelligence (LasINT).

Indeed, understanding and countering laser threats requires more than hardware. It demands intelligence - knowledge of what lasers are being used, how they are deployed, and how they are evolving. By collecting and analysing data on enemy laser activity, militaries can gain insights into enemy tactics, techniques, and procedures.

This emerging field is known as laser intelligence, or LasINT. Sentinel Photonics is one of the few companies with LasINT expertise. Its engineers and analysts track global developments in laser-based detection, mapping out known wavelengths, pulse patterns, and delivery systems. This insight enables more effective countermeasures - not just for today's threats, but tomorrow's, too.

In tests, Sentinel has been able to use the newest threats to demonstrate weaknesses in a defence team's capabilities. This is in part because of its heritage in collecting and understanding lasers. It's this intelligence that enables Sentinel to provide a comprehensive laser protection capability, updating the specification and performance of protective filters in response to battlespace trends.

Proven and robust

The Sentinel Photonics team has over two decades of experience in laser systems, optics and threats. It manufactures state-of-the-art laser detectors and filter systems and provides consultancy to mitigate the latest laser threats.

On today's battlefield, optics are essential yet exposed. As laser threats proliferate, the ability to remain undetectable becomes increasingly difficult. Retroreflection is a quiet vulnerability with big consequences, and traditional defences are no longer enough.

FROST gives dismounted soldiers, special forces and vehicle crews a vital edge: the power to see without being seen.

For more information please visit:
https://sentinelphotonics.co.uk