The Romance of Laser Weapons

Visions of Pinpoint Control

By MANUEL GARCIA, Jr.

The US Senate "has embraced last year's Defense Science Board conclusion that directed-energy weapons -- such as high-, medium- and low-power lasers -- hold great potential and should be developed as soon as possible. In the fiscal 2009 defense authorization bill, which was approved Wednesday [17 September], the Senate included additional funds for laser programs and a provision requiring Defense Secretary Robert M. Gates to accelerate work that would make directed-energy weapons operational in the near future." So reports The Washington Post.

The impetus behind this push is a vision of having invincible control by being able to project destructive power instantly along lines-of-sight onto objects identified as threats or obstacles.

This vision is as old as the Perseus myth, with Medusa's petrifying death-ray vision. Just over a century ago, during the birth of modern physics and electrical technology, the vision was updated by H. G. Wells to that of a Martian heat ray (in his novel "The War Of The Worlds"). For the last 48 years, the vision has been a fantasy halo around laser technology.

What is a laser? How can it be used as a weapon? What are the major obstacles to devising laser technology for realizing the vision of petrifying control?

A laser is an electro-optical devise that emits a beam of coherent light. "Coherent" means the light is like a single wave (the phases of many wavelets are aligned into a single entity), which does not disperse (spread out, dissipate) as it propagates. Another feature of laser light is that it is monochromatic, or made up of a very narrow band of frequencies (colors). The idea of a laser weapon is to produce a very powerful beam and to rely on its speed-of-light straight-line non-dispersing propagation to deposit energy on a distant target, where it is ultimately absorbed as heat.

The physics of lasers is based on the quantum physics of atoms (and molecules) and the statistical mechanics of large ensembles of atoms or molecules as fluids (gases or liquids) or solid-state materials, like crystals. Let us describe lasing by the use of simple analogies, which are suggestive but not quantitative.

An atom is the basic unit of matter for any of the 115 chemical elements (of which only 92 occur naturally). An atom can hold energy up to a maximum amount without changing its mass or charge (without emitting electrons or undergoing nuclear fission). One could imagine an atom to be analogous to a drinking glass, and the level of water in the glass analogous to the energy it holds. This is a continuous model of energy storage in an atom, and it is wrong. Atoms store energy in discrete bundles, or quanta, and the detailed description of this phenomenon is called quantum physics. We can imagine an atom as analogous to a macroscopic vertical pole along which a series of baskets is attached, and with the spacing between baskets diminishing as the height increases. Consider these baskets being numbered upward, 1, 2, 3, etc. A ball resting in a basket indicates the quantity of energy held by the atom. Were the atom a continuous system (the glass of water) then any incremental amount of energy could be poured into it, up to "the rim." However, for our quantum basket system, energy can only be absorbed if it is delivered in a bundle that exactly matches the spacing to a higher basket above the ball, for example from #3 to #4, or from #3 to #6.

Another feature is that the atomic energy level system is dynamic. Each energy level has a unique maximum lifetime; in general, maximum lifetimes diminish with height (energy level). The ball will remain in a particular basket until:

1. the maximum lifetime for that level has elapsed, so the ball falls to a lower level and a bundle of radiation called a photon, equal to the energy drop (e.g., from #6 to #1), is emitted; this is called spontaneous decay;

2. an incident photon excites the ball up to a higher level prior to spontaneous decay;

3. an incident photon whose energy matches a downward transition (e.g., from #3 to #1) causes the ball to drop and a second photon with the same energy, phase, frequency, polarization, and direction of travel is emitted along with the first photon; this is called stimulated emission;

4. a collision with another atom (or molecule, or ion) causes the ball to drop and the energy released to be parsed into some combination of a quantum of radiation and quanta of energy absorbed by the colliding particles.

Stimulated emission is the essence of the lasing process and was incorporated into the name "laser," Light Amplification by the Stimulated Emission of Radiation.

The laser medium is an ensemble of a vast number of the atoms or molecules whose energy levels are being exploited. The statistical mechanics of this process are -- very approximately -- as follows. Because the maximum lifetimes in energy levels generally diminish as they are "higher," most atoms are found to be in low energy levels at any given instant. As particles absorb and emit photons, and collide into one another in fluid media, or continuously vibrate into each other in solid-state material, they bump each other up and down in energy level so that on average most reside in low energy levels at any given instant, and decreasing fractions of the entire population are to be found at increasingly higher energy levels. This population distribution is stable over time, even though any single atom will jump chaotically from one state to another, over its entire sequence of possible states, as energy flows into and out of that atom from instant to instant. (In this regard population distributions of quantum energy systems are dynamically egalitarian in comparison to the stagnant population distributions of wealth in our national systems.)

Lasing is accomplished in four steps: 1, pumping a population inversion; 2, creating a cavity resonator; 3, coherently amplifying a selected frequency (color) of light by avalanching a matching stimulated transition, and; 4, depopulating the lower laser level and removing waste heat from the medium. Each of these steps is described in turn.

External energy is used to impulsively excite an unnaturally large number of atoms from their typically low energy levels up to a significantly higher "upper laser level" (say, level #10). During the lifetime of this upper laser level there will be fewer atoms of lower energy at the "lower laser level" (say, level #9). This is a population inversion; it is analogous to a wealth profile in which all/most/many of the people who had been making $30K/year simultaneously win lotteries putting them at $30M/year, so that suddenly there are more people at this bracket than at, say, $10M/year. The energy to pump a population inversion is often in the form of photons from flashlamps or light-emitting diodes. For some fluid lasers, the energy can be introduced by chemical reactions, or by electric discharges freeing electrons that collide into atoms and molecules to excite them, or by the supersonic expansion of molecular gases whose rapid cooling and rarefaction stops particle collisions and allows an unnatural number of molecules to remain in a particular high energy state for its full lifetime, and thus exceed the population of some lower state.

Any population inversion has a finite lifetime, which might be quite short, and is spatially localized in a manner dependent on the medium and the pumping mechanism. A laser is designed so that the population inversion occurs within a cavity, generally a tube (real or virtual) with mirrored inside end-surfaces. The length of this cavity is carefully set so that the period of time over which a light wave bounces between the mirrors is smaller than the expected lifetime of the population inversion, or maximally, equal to it. This is a cavity resonator.

The lasing process is initiated by either the spontaneous occurrence or the intentional introduction of a small flux of photons whose frequency matches that of the desired laser de-excitation (from upper laser level to lower laser level). As these seed photons resonate between the mirrors, they stimulate an avalanche of emission from the selected laser transition. Because of the population inversion, downward transitions from the upper laser level (stimulated emission) outnumber upward transitions from the lower laser level (absorption). This avalanche occurs coherently, the phases of the emitted photons align because of the quantum physics of stimulated emission and because of their presence within the resonator. The seed wave or beam is amplified because it has absorbed the energy of the population inversion, which is destroyed in the process. The amplified, monochromatic, coherent beam can be emitted from the cavity by suddenly moving a mirror, or by allowing one of the mirrors to be partially reflecting and partially transmitting.

The final step to lasing is to return the medium to a condition where it can be reused. Whether a laser is a pulsed or continuously operating device, the population distribution of the medium must be returned to its initial state so that the pumping mechanism can produce another, or a continuing, population inversion. This means that the lower laser level must be depopulated to ensure that subsequent pumping produces a population inversion between the two laser levels. The energy held by molecules excited to the lower laser level must first be spread among even lower levels, and then removed entirely from the medium as waste heat. If this energy is not removed then the statistical mechanics of the medium (particle collisions) will push some of it back up into higher levels and work against the effort to produce a population inversion. Another detrimental effect of excess heat in the medium is that it can create pockets of varying density, which can spoil the passage of laser light through it in a manner quite similar to the "heat waves" and mirages one can see through unevenly heated air along desert terrain or hot asphalt roads. Excess heat can also crack crystalline media.

Lasing is an inefficient process, and lasers can require high precision components (mirrors, windows) in contact with energetic or corrosive environments (high ultraviolet flux, chemicals, electrical discharges, heat). Lasers require relatively large pump power supplies, and active cooling or long duty cycles; the output power of a laser is limited by its cooling needs. The reliability and robustness of a laser is limited by that of its high-precision and delicate components, usually its mirrors and windows. "Weaponizing" a laser system is an exercise of integrating all the necessary components into as compact and robust a package as possible. Obviously, this becomes more of a challenge as the laser become more powerful. We can surmise that the major obstacle to fielding lasers of the immense power desired by military planners is that their pump power supplies cannot yet be made small enough, or with sufficient energy storage capacity, to carry on small mobile platforms (tanks, trucks, patrol boats, fighter and ground attack aircraft, and individual troops).

How are lasers to be used "in combat?" Let's quote The Washington Post again, on: Lasers as anti-personnel devices,

Low-power lasers known as "dazzlers" are being used in Iraq, mounted on M-4 rifles, "to warn or temporarily incapacitate individuals," according to the Defense Science Board's report. Army, Special Forces and more recently Marine units are using them to warn or deter drivers approaching checkpoints and to "defuse potential escalation of force incidents," according to the report. Marines were given approval to use a green laser whose beam can temporarily reduce a person's vision when aimed from a distance of 1,000 yards, according to the report. These "laser optical incapacitation devices" were being procured on a case-by-case basis. Laser use remains controversial because a protocol of the Geneva Conventions bans their use in combat when they are designed to cause permanent blindness. Two years ago, when the lasers were introduced in Iraq, Army Lt. Col. Barry Venable, a Pentagon spokesman, said the devices were legal. "They don't blind people," he told reporters. "It's like shining a big light in your eyes," he said, adding that he did not know how long the "optical incapacitation" lasted.

Laser and electro-optical technology for spying and assassination,

A 2004 [Defense Science Board] report recommended a "Manhattan Project" approach to take "available and emerging technologies . . . to identify objects or people of interest from surveillance data and to verify a specific individual's identification." It suggested that "biometrics, tags, object recognition and identification tokens" be harnessed with sensors and databases "to overcome the shortcomings of conventional intelligence, surveillance, and reconnaissance systems." Tags allow distant tracking or detection. Some tags are active, emitting radio waves that can be collected. Others are passive, including chemicals that give off a color when hit by an infrared beam. The board said these "represent a very important area for research and technology development..." A recent congressional report said Special Forces in Iraq are using newly developed "sophisticated capabilities to identify, find, track, and kill or capture high-value individuals."

Lasers as aerial ground-attack weapons,

The science board said tactical laser systems could be developed for broader use because they "enable precision ground attack to minimize collateral damage in urban conflicts." The report suggested, for example, that "future gunships could provide extended precision lethality and sensing."

Lasers as ground-to-ground and ground-to-air weapons,

The board also proposed using lasers to protect against rockets, artillery, mortars and unmanned airborne vehicles by blasting them out of the sky. Last month, the Army awarded Boeing $36 million to continue development of a high-energy laser mounted on a truck that could hit overhead targets. But deployment is not expected until 2016, even if all goes well.

Imperial impatience in realizing its vision of control,

The Senate Armed Services Committee, in its report on the fiscal 2009 authorization bill, asked about the progress of lasers. "Years of investment have not resulted in any current operational high-energy laser capability," the committee noted in its report...The Senate committee was critical of the "airborne laser" program, a first-generation missile defense system. It held back $30 million from next year's budget and said funds for a second version would not be authorized until the first shoot-down test from a 747 aircraft is conducted at the end of 2009. More information is needed to determine whether the system "could eventually provide a militarily useful, operationally effective and affordable missile defense capability," the panel's report said.

It is probable that laser weapons and other military electronic and electro-optical identify-track-and-kill technology will be used to eliminate specifically targeted, usually poor, darker-skinned individuals in far-flung "low intensity" "war on terror" zones, at a cost per kill that will exceed the entire cost of sustaining that person's existence from conception, through maternal care while in utero, through family life, though education and maturation, to rebellion, to imperial inconvenience, to the moment of elimination. This is like the insanity in the homeland of sinking over $20,000/person/year for 1 percent of the population to be in prison, $60B/year. "Like many other states, California spends more on prisons than it does on higher education. Forty per cent of prisoners cannot read." I can imagine the assassinations our Special Forces and techno-warriors will carry out with GPS linked laser weapons, remotely piloted vehicles and electro-optical surveillance technology, will easily cost an order of magnitude more, hundreds of thousands of dollars per elimination, and perhaps many millions per hit if one divides the full cost of technical development and field operations across the actual number of subsequent eliminations.

Why are we planning for so many of today's homeland children to be tomorrow's convicts, by sinking money into more prisons yet refusing to sink that same money into the designated ill-fated youth: for education, for child-care, for supervised recreation, for job training, for mental health, for family support, for decent meals, for simple demonstrations of love for them? Why wait? Similarly, why are we willing to spend so much to kill off the most rebellious of foreign peasants and proletarians who oppose our imperialism, our obsession to control, when we could more easily have lifted their societies to greater prosperity, health and security with the same cost, and found ourselves surrounded by a world of friends instead of "terrorists?" Euripides wrote "whom the gods would destroy, they first make mad" (in Longfellow's rendition), and we in the US Imperium are truly mad, obsessed with our greed and lacking character, we can only run our economy as a pork barrel feeding frenzy while terrified by everything and everyone. Funding military technology and the prison industry slops many prized corporate hogs and trickles down to many grasping little constituencies, and the hard assets finally produced from these "building programs" can be thrown against the tribes of dark outsiders who frighten the "us" who have the self-bestowed right to be frightened, and thus the right to control everything in order to drape that fear with denial -- and to kill.

Manuel Garcia, Jr. is a retired physicist. E-mail = mango@idiom.com