Can all electromagnetic spectra be focused like a laser?

Question

Lasers have a wide range of applications, but can be very costly to produce at high power/intensity. Since light is nothing more than a narrow band of the electromagnetic spectrum, it makes me wonder if the same high power/intensity applications can be achieved at a lower cost by concentrating other wavelengths (e.g. Infrared, radio, etc.)

A cursory google search revealed nothing of this sort, which makes me suspect that i this is not possible. But i just want a clear answer as to whether other electromagnetic waves (besides light) can be concentrated and propagated as a beam invthe same way as a laser. If possible, i'd also like to understand if/why larger wavelengths hinder our ability to concentrate these waves into high power/intensity applications.

Answer 1

Yes, other electromagnetic radiation can be focused, and routinely is. Basically, everything up to x-rays can be focused relatively easily. Once you get to energies so high that they go right thru most material, using these materials to focus such rays gets tricky or impossible. For example, I don't think we know of a way to focus gamma rays.

On a cosmic scale, gravity can be used to bend the path of radiation, which works for all wavelengths. It is currently beyond our capabilities to construct devices that do this in any meaningful way, but we can and have made use of the ones that occur naturally. Distant galaxies are sometimes used by astronomers as gravitational lenses to see more clearly things that are even more distant behind these galaxies.

For most electromagnetic radiation, there are two ways we can change its propagation path, refraction and reflection. For visible light, this is done with lenses and mirrors, respectively. Finding a structurally suitable material that is transparent at other wavelengths (like glass is at visible wavelengths) can be difficult, and most focusing of wavelengths far from the visible spectrum is usually done with reflection rather than refraction.

Examples of reflection used to focus non-visible radiation abound. Old UHF TV roof antennas were commonly corner reflectors. These has a series of rods that formed a V-shaped pocket pointed in the direction of the transmitter. The actually antenna was a split rod or sometimes a series of rods inside the V. Other antenna systems use unconnected conducting rods and other conducting objects to reflect the radiation to increase its flux at the actual receiving (or transmitting, antennas work equally both ways) element.

Large radar dishes or radio-telescopes are examples of extreme focusing of radiation, usually in the GHz range.

At long enough wavelengths, yet another method can be used to make a focused beam of radiation. This is done by controlling the phase of multiple emitters. As a simplistic example, consider two vertical radio antennas spaced 1/4 wavelength apart. Antenna A is fed with a signal that is 90° ahead of that to antenna B. Imagine a wavefront emitted from A. After 1/4 cycle it reaches B, which is now emitting the same signal. The two wavefronts emitted by A and B add, and the signal appears strong to someone receiving in the B direction. Now imaging a wavefront leaving B. When it gets to A, A is emitting 1/2 wavelength ahead, which is 180° out of phase. The two signals therefore cancel each other in the A direction.

This basic principle, called a phased array, can be applied to a large number of individual transmitters (or receivers, works both ways). With lots of individual elements in the phased array, a very narrow beam can be emitted (or again, the overall antenna can listen in a narrow direction). A great example of this is the Aegis radar system originally deployed on the Arleigh Burke class of destroyers. The large hexagonal patches on the front and sides are actually arrays of many small radar antennas, with the phase shift of each being controllable dynamically. This means the beam can be re-directed very quickly electronically without requiring a mechanical sweep of a physical antenna.

This principle can also be used to steer a reflected or transmitted beam. At optical wavelengths, this is usually called a diffraction grating. A series of parallel scratches separated by a fraction of a wavelength is etched onto a mirror. At the right combination of wavelength and reflection angle, the reflections from each of the peaks are either in phase and therefore add, or are out of phase and cancel each other. Since the angle they are in phase at is a function of wavelength, such diffraction gratings can be used to separate light by its wavelength.

These parallel scratches can also be applied to the surface of transparent objects. When you look thru one at a thin vertical slit of white light aligned with the scratches, you see it spread out horizontally into its component colors. Some spectrometers work on this principle. I have heard of one effort to use this effect to focus x-rays.

Answer 2

You might be interested to learn that not only are there microwave (and IR, and X-ray ... ) lasers, but that some of these "devices" can even occur naturally in gas nebulae in space.

From the wikipedia article on Megamasers,

A megamaser is a type of astrophysical maser, which is a naturally occurring source of stimulated spectral line emission.

There is currently a lot of research on x-ray lasers, which have existed for decades but are now being brought down to bench / desktop sizes. These devices generate pulses of coherent x-rays at 10 – 20 nm wavelengths.

Answer 3

From the comment of @Dan and the linked Wikipedia article on masers:

When the laser was developed, Townes and Schawlow and their colleagues at Bell Labs pushed the use of the term optical maser, but this was largely abandoned in favor of laser, coined by their rival Gordon Gould. In modern usage, devices that emit in the X-ray through infrared portions of the spectrum are typically called lasers, and devices that emit in the microwave region and below are commonly called masers, regardless of whether they emit microwaves or other frequencies.

Gould originally proposed distinct names for devices that emit in each portion of the spectrum, including grasers (gamma ray lasers), xasers (x-ray lasers), uvasers (ultraviolet lasers), lasers (visible lasers), irasers (infrared lasers), masers (microwave masers), and rasers (RF masers). Most of these terms never caught on, however, and all have now become (apart from in science fiction) obsolete except for maser and laser.

From this, everything is either called a maser or a laser. Also, let's ignore the debate about whether all of the letters need to be capitalized or not.

Answer 4

I would just like to add, in addition to the other answers regarding the EM spectrum, that anything that follows the wave equation can be focused because all of the principles of constructive and deconstructive superposition apply.

Things outside the EM spectrum that follow the wave formula include pressure waves (when focused, commonly referred to as sonar), and even matter waves, such as focused ocean waves, called rogue waves.

Answer 5

phased array directs specific beam, but it requires many MANY minute beams, the entire array active doesn't detect. Hypothetically all EM spectrums can be phased array to be directed, however it's best at radio and microwaves, the typical communications/sensor medium. Anything above Visible light (UV, Gamma) runs ultra high frequency . As for Lasers we already have

• UV Lasers
• X-Ray Only gamma remains difficult hypothetical research.