A Very Brief Guide to Femtosecond Lasers

Lasers emit light either continuously or in a train of pulses. Under the heading of ultrafast lasers falls a certain group of lasers that produce picosecond, femtosecond or even nanosecond pulse durations at different repetition frequencies. Within this group, femtosecond lasers emit optical pulses with a pulse duration in the domain of femtoseconds (1 fs = 10-15 s) typically ranging between a few femtoseconds to hundreds of femtoseconds.


How Does a Laser Produce Femtosecond Pulses?

Technically, different types of lasers are able produce femtosecond pulses. Among them are solid-state bulk lasers, fiber lasers, dye lasers, and semiconductor lasers beside some exotic types. So how could you bring a laser to emit pulses instead of continuous wave emission?


In nearly all cases it happens in the resonator of the femtosecond laser. Light that is trapped inside an optical resonator forms a certain number of standing waves that differ in their wavelengths, in agreement with the resonance condition. The broader the spectrum of the laser light the more standing waves or modes exist inside a laser resonator. The number of these modes also depends on the spectral range of the gain medium of the femtosecond lasers.


The actual technique used to generate a laser pulse within the resonator is called mode locking. Normally, all these resonator modes oscillate independently in a random manner. Mode locking means that resonator modes are forced to oscillate in phase which consequently leads to mode interference and thus to a sharp laser pulse that travels in between the resonator before it exits in one direction to emit a single laser pulse. In principal, the more modes that are phase locked in their oscillation, the shorter the pulse duration that can be achieved. Femtosecond lasers do not only differ in their pulse duration but also in the repetition frequencies of the pulses. They can range from several MHz to GHz.


Advantages and Applications of Femtosecond Lasers

Femtosecond lasers focus the energy on a very short time scale within a single laser pulse. That leads to high peak powers which are far beyond power peaks achievable by continuous wave lasers. Delivering ultrafast high intensive laser output opens new possibilities for all kind of laser applications.


In industrial applications such as material processing, the ultrashort pulses lower the thermal damage to the material. Basically, the laser pulse acts as a spatially confined, intense heat source that evaporates material in the focal spot very rapidly without strong heat dissipation into the surrounding area.


Another advantage for new applications is the extremely short duration of the laser pulse that enables the use of femtosecond lasers to observe and manipulate ultrashort processes for example in biology or chemistry.


Femtosecond Lasers from Novanta

Novanta has developed femtosecond laser technology and application based systems that offer unique capabilities for a variety of applications. The taccor laser family brings you turn-key systems with repetition rates from 1 GHz to 10 GHz in a mono-block design that combines a pump laser and oscillator. The venteon family comprises few cycle femtosecond lasers with broadband spectral pulses and a focus on individual specification demands. The helixx laser offers 250 MHz repetition rate with a variable emission wavelength while the gecco family offers a choice of the repetition rate between 70 and 110 MHz and two pump lasers. Find out more about our femtosecond laser products or simply contact us to learn more.