annoying but only a threat as a distraction
Info below may calm things down a bit..... from company memo
(thanks to a certain Pete W)
Recent media reporting of laser light “attacks” on aircraft has been the subject of tabloid reporting and has been frequent enough to be of some concern to xx Pilots.
Optical masers as they were first called, were developed in the late 1950s and early 1960s.
The first working *laser used a ruby crystal as the resonator cavity that was optically pumped by a very high output xenon flash tube.
Its inventor, the late Dr Theodore Maiman recounted: "One reporter came up to me and asked me about using the laser in developing weapons. I told him I didn't think it very likely.
He asked me if I would deny that the laser could be used that way, and I said no”.
The very next day, all across the USA, headlines shouted: “LA Man Discovers Science- Fiction Death Ray! ” Hence, while laser technology has progressed significantly in the last 50
years, it would seem tabloid journalism standards sadly have not. Lasers are now found in devices as diverse as the IRS systems on the B744 to supermarket checkout scanners.
Tabloid press aside, should you still be concerned about your vision if the aircraft you are operating is illuminated by laser light? The short answer is no.
Contrary to popular belief, all but the most powerful continuous wave lasers give out little more light than a good “Maglite” torch. The laser, however, emits all of its light in a very narrow wavelength, over a pencil thin area and also has a property known as coherence. It is this latter property that allows lasers to be focused with incredible precision hence high power
units (ie. power rating of at least several watts) be used for cutting and etching in industry.
Unlike megawatt, precision gas or ruby laser systems (read: more text-book like properties, not portable and require governmental budgets) used, for example, at professional observatories for lunar ranging experiments, the milliwatt lasers used to capture headlines and “tag” aircraft are, almost without exception, inexpensive diode based green laser “pointers”. Their wavelength (525nm) is very close to that of the peak spectral sensitivity of the human eye at 555nm.
Virtually every green laser pointer uses Diode Pumped Solid State Frequency Doubled (DPSSFD) laser technology. These devices use a “pump” laser diode which has its frequency doubled by a Potassium Titanyl Phosphate, (KTP) crystal inside the laser cavity. The visibility
of these green pointers appears to the eye to be about six or seven times brighter than the older 670nm red diode based laser pointers, rated at the same power output. Diode lasers also lose their coherence at small distances, typically less than a metre.
Beam divergence, or the spot diameter at a distance, of these diode based lasers is a little underwhelming. Without a corrective lens these devices are rather like dim coloured flashlights and have very poor “beam” qualities. A small lens is required to collimate the diode’s output into a usable beam.
Due to their fairly cheap manufacture and lack of precision these lenses typically allow the
beam to diverge about 2mm per metre from the source diode. Hence, at around 500 feet a 1mm beam has diverged to approximately 300mm in diameter.
Let’s assume a “worst case scenario”. Our laser “tagger” has acquired a green hand held laser which is rated at the highest power current technology allows (around 400mw) selling for approximately $A1700.00 (most, however, are less than -one tenth that power level and sell for under about $100).
From before, the spot size at 500 feet is approximately 300mm. The pupil of a dark adapted
human eye is typically 6-7mm in diameter. Hence, the total possible flux that can enter a
Pilot’s eye is around one sixth of a milliwatt. This is about 2.5 times less than continuous
direct exposure to a Class One laser held directly to an eye, while not recommended practice,
is considered to be safe under all conditions. (I have ignored atmospheric scattering and
absorption plus reflection and attenuation losses from flight deck windows, which would
significantly reduce any incoming light).
Of course, a sudden flash of bright green light from the ground could be distracting, and must
not be condoned, but fortunately is no more a “death ray” or “weapon of mass murder” than the Maglite found in many Pilot’s navbags.
A secondary effect of bright light, laser or otherwise, is the temporary bleaching of the photo pigment in the retina. An everyday example of this is after having your picture taken at night,
when you may see the “afterimage” of the photographer’s flashgun etched into your retina for a time.
This physiological reaction is perfectly normal and will pass after a few minutes.
If you are flashed by a laser from the ground I would, however, recommend the following.
1. Do not look directly into the beam.
2. While the possibly of distraction exists, both the power and coherence of green laser
pointers is trivial and it is virtually impossible for your eyes to be injured from an event above an altitude of approximately 250 feet.
3. Continue with normal and safe operation of the aircraft, for example, in a manner similar
to driving at night with an oncoming motor vehicle that does not dip their headlights.
*Laser is an acronym for Light Amplification through Stimulated Emission of Radiation