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 nanosecond (1 ns = 10-9 s), picosecond (1 ps = 10-12 s), or even femtosecond (1 fs = 10-15 s) pulse durations at different repetition rates. This fastest group, femtosecond lasers, emit optical pulses with a duration 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, semiconductor lasers, and some exotic types as well. So why do some lasers emit pulses instead of continuous waves?
In nearly all cases for the femtosecond laser, this pulsing happens in the resonator. 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 laser.
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 forces the resonator modes to oscillate in phase. This consequently leads to mode interference and thus to a sharp laser pulse that travels within the resonator before it exits the laser and emits a single laser pulse. In principle, 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 emit a single pulse of energy within a very short time scale. This leads to high peak powers that are far greater than those achievable by continuous wave lasers. Delivering ultrafast, high intensive laser output opens new possibilities for all kinds 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 vaporizes material in the focal spot very rapidly, without strong heat dissipation into the surrounding area.
Another advantage of the extremely short duration of the laser pulse is to enable the use of femtosecond lasers to observe and manipulate ultrashort processes, for example the reaction rates and mechanisms in biology or chemistry.
Femtosecond Lasers from Laser Quantum
Laser Quantum has developed femtosecond laser technology and application-based systems that offer unique capabilities for a variety of purposes:
- The taccor laser family provides 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.
- The gecco family offers a choice of the repetition rate between 70 and 110 MHz and two pump lasers.
To request more information or a quotation for these or other Laser Quantum products, contact IL Photonics.