Understanding Photonic Barriers
A Master Class in Low-Light Fighting Science by Chuck Pressburg
Credits and description of terms:
Before I begin the body of the article I feel it important for the reader to know a couple of things so that we are on the same sheet of music and the reader does not become overly confused by the various terms used in the article.
The term Photonic Barrier was coined in modern night vision tactical training by John “Chappy” Chapman of LMS Defense. Although I was very familiar with photonic barriers in real world applications over my 26 years of SOF experience, in the military we always called it “whiting out” or “Blooming” which were descriptions of what we were seeing in our Image Intensification(I2) devices. When you become savvier about how these devices work it becomes very clear that Photonic Barrier is the perfect label for the phenomenon covered in this article and when I heard Chappy say it for the first time it was like a bolt of lightning hit me. Of course that’s how we should refer to this subject matter. So consider this first paragraph a hat tip to Chappy, not only for coming up with a scientifically accurate description but for pushing Night Vision Training to Law Enforcement and Civilians while I was still out getting after it night after night overseas and unable to spread the Night Vision “Gospel” to domestic LE.
NVD (Night Vision Device), NOD (Night Observation Device), NVGs (Night Vision Goggles), Green TV, Green Screen, and Starlight scopes. All of these terms are interchangeable when it comes to the context of this article. We are talking about amplifying visible light to produce an increased situational awareness of what’s around you. The end users routinely use the term Infra Red to describe this, but that is not entirely accurate. Near IR spectrum above 700 Nanometers (nm) and below 1mm (or Micron) along the spectrum of light is where we are talking about. Specifically 850-900 in that ball park. For the purpose of this article the term IR pointer or IR illuminator are actually referring to this spectrum. I’m merely choosing to use common vernacular used by the people who normally employ these systems. Consider IR pointer a slang term and if it gets the point across, I’m sticking with it. So now that we have the techy boring stuff out of the way, let’s talk about operating under green screen in practical application.
Students and Agencies often ask me questions about weapons mounted lasers and performance characteristics.
Like good shoppers they want….NO, They NEED to know what the numbers mean and which numbers really matter. When it comes to Near IR laser pointers and illuminators, power matters and power is expressed in milliwatts of output (mW). As a general rule more mW of power is always better, as long as it is adjustable and can be used at less than maximum settings
Why is power important? The simple answer is that if it is really dark outside and there is very little ambient light you can get by with very little power because your Night Vision Device (NVDs) will process the near IR photons like a starving man devours water at an oasis in the desert. The intensifier tubes in the NVDs are greedy and needy for photons (light) and they will take as much as they can get paying the most attention to the most powerful light source within the field of view of the objective lens of the NVD. So if you are on a ranch in Texas trying to spotlight hogs or vermin with your suppressed rifle and NVDs on a no moon night even “the stars at night being big and bright deep in the heart of Texas” will not compare to the NIR energy of even a class I eye-safe laser pointer or LED IR illuminator and you should not have any issue seeing in the dark or identifying your aiming laser’s location within your field of view.
“So why is more power usually better”?
Unfortunately Police and Military serving in urban areas rarely if ever operate in an environment devoid of ambient light. This is where the problem of photonic barriers comes into play. Remember when I said that Image intensification tubes were attracted to the brightest light source? Because of this, NVDs will often get a blooming effect around the most powerful light source in the field of view. If that light source is between you and an area that you wish to observe, the NVD will highlight the light source and the area beyond it may seem invisible or may appear as a darkened shadow. The light is causing a wall between you and what you want to see. This phenomenon is referred to as photonic barrier. The way to overcome the barrier is to bully the intensifier tubes into doing your bidding by throwing more NIR energy where you want to see than the amount of light being put off by the photonic barrier light source.
Projecting NIR laser energy beyond photonic barriers like porch lights or street lights with enough concentration and power output will cause the intensifier tubes to process this new energy source and show contrast within your image, illuminating the previously shadowed or invisible area, much like shining a flashlight into a dark corner.
Illuminator output and adjustability are key factors in “Duty Grade” weapons laser selection. Too many LE agencies run laser systems that are grossly underpowered for the jurisdiction that they are responsible for. For example let’s say that you are a responding SWAT officer to a terror or active shooter situation where the suspects have gone dynamic on foot. The Boston Bombers’ apprehension is a good example of this kind of situation. Due to your recent night weapons training and NODs usage, the decision to use NODs to gain an advantage is made and a neighborhood search is ordered. As your officers skirt along houses looking into bushes and in back yards your team is pulling 360 security. Officers looking across the street at a two story building have a street light on the far side of the street in front of the building. Through their High FOM autogated tubes in their PVS31’s (that UASI paid $15,000.00 each for) ALL windows on the far side of the street look like giant black rectangles. The street light illuminates the face of the building but the energy does nothing to illuminate the spaces beyond the windows. You are being blocked by the photonic barrier of the street light. This is the moment that you realize that you didn’t know what you didn’t know and your teams’s LE laser policy and purchase decisions to go with Class I eye safe lasers with adjustable diode IR laser illuminators was a terrible choice. As your team mates fire up their illuminators on their DBAL or ATPIAL-C’s you realize you don’t have enough energy to burn through the light energy from that street light.
Now, let’s look at that exact same situation but with a team that has a well researched and thought out Night Vision Policy that has properly justified the need for Class IIIB lasers and illuminators or at LEAST class I lasers with illuminators that are not splitting a single low powered illuminator diode and a beam splitter. You are in the exact same situation except when your officers attempt to see across the street into the building windows, the officers see that their wide field of view illuminator setting that they had been using to search in the bushes cannot burn past the street light photonic barrier, so they quickly increase power and narrow the beam to concentrate 150mW of power into a tight 6 degree spot of clean IR energy. Like a giant spotlight the IR energy spills into each room through the previously blackened windows. The outline of one of the shooters is clear in one of the second floor windows. He is standing back away from the window about 4 feet deep in the room and the outline of the AK-47 contrasting against the shooters shirt is clear in your NODs. Congratulations, you have found your bad guy.
“If more power is better, then why not more power all the time”?
Remember that the tubes focus on the brightest thing. Well in dark situations high power floods and lasers will bloom you out in the darkness and you will create a photonic barrier on yourself. So it is important to have a multi-function laser system with adjustable power settings so that you have enough power when you need it but not too much when you don’t.
One should also keep in mind that anything on your weapon in front of and slightly offset from your laser emitters, can also reflect NIR energy back into your goggles causing a photonic barrier. Laser placement on the rifle and the location of back up iron sights, flashlights, slings, etc. should always be taken into consideration. It’s always a good idea to “play legos” on your duty gun and anytime you move stuff around, go in a dark room or outside at night and test fire your laser and illuminator to ensure that you have not changed something to create a photonic barrier. This is a MUST prior to zeroing your newly mounted laser. Laser zero can be a time consuming process. Don’t wait until AFTER you have the laser bolted on and are halfway done zeroing it, that you want to move it to a different location and have to start all over.
Prior to purchasing lasers for your dept or team, request a consult with a Night Vision Subject Matter Expert (SME) or professional training entity for a night vision course. Too many dept’s buy first, then when they bring in a professional trainer and realize what a laser NEEDS to be able to do, they realize that they listened to some sales dude somewhere and they have bought the wrong stuff. IR illuminators are to Night Vision operations what weapon mounted flashlights are to low light operations. TAC officers want the brightest flashlight they can get to process information, right? If you are rocking some class 1 or 1033 DRMO laser on your duty gun now, roll that sucker over and read the data plate on laser. The output for the pointer and illuminator will be listed. If your IR illuminator is below 125mW you have the NIR equivalent to the Sure-fire 6P. I had a 6P on my M-16 in 1991….. The military has not upgraded their rifle lasers since 2003. Would you issue 13 year old armor? Flashlights? Vehicles? “If it’s good enough for the military” is not an acceptable justification for an NIR laser procurement.
Research, Train, Buy….. you won’t regret it.