Overview
A laser is a light source with three important characteristics. Laser light is monochromatic, meaning the light is highly concentrated around a central wavelength, with very little emitted at other wavelengths. It is also directional—its energy can be concentrated into a small spot, significantly increasing intensity and making lasers useful for applications that require precision and high energy density, such as cutting, welding, and surgical procedures. Finally, it is coherent, which means that the light waves of the laser beam repeatedly reach the same peak or trough at the same point in time and space. This property is useful for laser-based measurement and sensing applications.
Lasers typically involve a power source (a pump), a gain medium (a material within which the energy supplied by the pump is turned into laser light), and a resonator that encloses the gain medium. Progress in laser technology depends on advancing one or more of these elements and is generally measured with respect to five technical characteristics of the beam: higher peak power, more energy in the beam, higher average power, shorter pulse lengths, and a wider range of wavelengths.
The engineering characteristics of lasers are also an important aspect of how fast the technology advances. For example, different configurations of power sources, resonators, and gain mediums can result in lasers of different size, weight, reliability, cost, and other key features. Addressing these and other engineering issues helps take lasers from labs to the commercial world, where many nonresearch applications make important use of them.
KEY DEVELOPMENTS
Improvements in laser technology since its invention in 1960 have allowed light to be manipulated and used in previously unimaginable ways. Lasers now underpin a huge range of scientific and industrial applications, including the following:
- Military applications Lasers serve a variety of ground-based missions, including attacking satellites and short-range air defense‒countering drones, rockets, artillery, and mortar rounds. An important advantage of lasers in the latter role over conventional munitions is a lower cost per shot and potentially more rounds in their magazines (assuming their power supplies are not exhausted). An important disadvantage is that rain, fog, and smoke potentially limit a laser’s range and beam quality.
- Communications Lasers can be used to transmit data between orbiting satellites. Compared to traditional radio transmission systems, laser communications allow for data-transfer rates that are 10 to 100 times faster. They are also more secure than radio systems because they have narrower beam widths that make them harder to intercept.
- Orbital debris removal Lasers may be useful for removing debris from low Earth orbit. By firing a laser pulse at a piece of debris, it may be possible to force the debris to de-orbit and burn itself up as it passes through the atmosphere.
- Imaging Pulses from an X-ray free-electron laser (XFEL) can penetrate through materials to image structures and measure a material’s physical properties. XFELs are particularly useful because the shorter wavelengths of X-rays allow better spatial resolution compared to visible light. In addition, they can emit very short pulses, which helps them excel at tracking changes over very short time periods.
- Materials processing Lasers can cut precise shapes, drill micron-scale holes, and deliberately deform surfaces to add stress to materials. Ultrashort-pulse lasers enable material to be ablated precisely with minimal damage to surrounding areas—a process useful in both manufacturing and surgery.
- Chip fabrication Lasers are used to generate a plasma, which is then stimulated to produce extreme ultraviolet (EUV) light to project a mask that carries circuit patterns onto wafers. Producing structures smaller than 2 nanometers on very-high-end chips relies completely on this technology, and these chips are critical for applications that demand high processing power, extremely energy-efficient operation, and miniaturization—requirements that characterize many systems of economic and national security importance.
