Ultrafast scientific lasers expand on their legacy

While ultrafast (picosecond and femtosecond) lasers are an essential subset of the lasers used today in industry and the medical arena (for example, machining glass for smartphone screens for the former, and laser eye surgery for the latter), it is the use of ultrafast lasers in research that allows such lasers to show their true colors, sometimes literally. Indeed, science is where it all began for these types of lasers, as the first ultrafast lasers were themselves research projects. Types of ultrafast scientific lasers include oscillators and amplifiers, either of which can be constructed using bulk or fiber-based components (or both). The use of fiber can lead to smaller, more rugged ultrafast scientific lasers, although fiber also has some intrinsic problems that must be cleverly managed: the high peak powers and the resulting high intensities experienced by the fibers (especially single-mode fibers) can lead to optical damage or to nonlinear optical effects. However, the latter can in some cases be put to good use—the outstanding example here is supercontinuum light sources, which rely on fiber nonlinearities to produce high-brightness broadband light. The ultrafast scientific laser category includes lasers that produce the shortest femtosecond pulses commercially available. Such lasers often rely on sophisticated techniques to produce high-quality pulses, such as carrier-envelope phase (CEP) stabilization, which ensures that the phase of each few-cycle pulse is correctly aligned to the pulse envelope. To create high-energy amplified femtosecond pulses that do not damage the components in the amplifier, chirped-pulse amplification (CPA) temporally stretches the seed pulse using a dispersive element before the pulse enters the amplifier; after amplification, the high-energy pulse is then temporally compressed. The evolution of ultrafast lasers over the years can be seen in a chart provided by fiber-based ultrafast laser maker Toptica (Munich, Germany). The first ultrafast lasers, based on a dye gain medium, were expensive and unreliable, while laser types based on solid-state gain media such as titanium sapphire (Ti:sapphire) and on optical fibers have high reliability and costs appropriate for commercial lasers (see Fig. 1).