femtosecond

A femtosecond is 10 to the power of minus 15 seconds, or 0.000000000000001 seconds. The prefix femto- follows the SI naming convention: kilo, mega, giga, tera, peta, femto, atto. At this timescale, light travels about 300 nanometers in a vacuum, roughly the wavelength of ultraviolet radiation. For industrial measurement and materials processing, femtosecond duration means the pulse has struck and left before thermal diffusion spreads meaningfully into surrounding material.

Femtosecond pulses are generated by mode-locked lasers, most commonly fiber lasers and solid-state lasers (often ytterbium or erbium doped). A mode-locked laser forces multiple longitudinal modes to oscillate in phase, producing a train of extremely short pulses rather than continuous output. Repetition rates range from kilohertz to megahertz depending on the cavity design and application. Peak power during a femtosecond pulse can reach gigawatts despite relatively modest average power, because the energy is compressed into an extraordinarily brief window.

Industrial applications

Femtosecond lasers dominate precision micromachining of metals, ceramics, glasses, and polymers. The extreme intensity concentrates energy in a tiny volume, ablating material cleanly without thermal damage to the surrounding zone. Holes drilled in turbine blades, surgical implant surfaces marked with micropatterns, and complex geometries cut into silicon all rely on this non-thermal ablation mechanism. The absence of a significant heat-affected zone means minimal burr formation, no melting, and no microcrack initiation in brittle materials.

In metrology and inspection, femtosecond pulses enable optical coherence tomography (OCT) and time-of-flight measurements with micrometer resolution. The short pulse duration determines the depth resolution achievable in optical slicing. Metrology systems also exploit the ultrafast nonlinear interaction: two or more femtosecond photons can be absorbed simultaneously, permitting direct measurement of surface features that would scatter a single longer pulse.

Femtosecond amplified spontaneous emission (ASE) and supercontinuum generation extend the technology further. When a fs pulse propagates through nonlinear media, its spectrum broadens dramatically, creating white-light-like output spanning visible and near-infrared bands. This supercontinuum enables broadband pump-probe spectroscopy and multiwavelength imaging in manufacturing diagnostics. However, femtosecond systems demand careful optical alignment, regular maintenance of the laser resonator, and awareness that cumulative exposure to ultraviolet output from frequency-converted pulses poses occupational safety risks.