Table of Contents
Ultrashort laser pulses and their challenges
The generation of ultrashort laser beam pulses needs careful monitoring of the light’s dispersion provided by a fiber laser. There is a dependency of phase velocity and frequency; a real laser beam pulse includes a spread in frequency, which will enlarge as it goes through an optical medium. Thus, simple, low-cost sources of sub-picosecond laser beam pulses, soliton fiber laser systems, including a laser diode and an optical fiber, are considered to become an ideal solution.
Balancing dispersion with Kerr focusing
This type of laser system allows decreasing the spread by “balancing it against Kerr focusing – the narrowing of a laser beam pulse caused when light’s electric field alters the medium’s refractive index – so each pulse travels as a soliton, and its duration remains unchanged.”
Limitations of traditional soliton fiber lasers
Soliton fiber lasers are regarded as very promising because of such benefits as simple construction; they are not able to reach the high energies of techniques, for instance, chirped-pulse amplification.
Overcoming energy constraints with new technology
New fiber laser technology allows overcoming these limitations. The operating principle of the fiber laser is based on the application of a spatial light modulator to manage the light’s dispersion relation to enabling higher laser beam energy pulses. A dispersion relation demonstrates how a wave’s frequency is relevant to its wavelength. “For light in a conventional soliton laser, the function is approximately quadratic, and its second derivative describes how a laser beam pulse would spread in the absence of Kerr focusing.”
Role of higher-order dispersion
Researchers from Australia have demonstrated that higher-order dispersion provides real benefits. A photonic crystal waveguide based on fiber laser technology has been developed, where the effects of second- and third-order dispersion were suppressed due to the waveguide’s geometry. The balancing process of fourth-order dispersion with Kerr focusing is connected to soliton formation.
Programmable spatial light modulators
The soliton fiber laser system acts by applying the same principle. The researchers employed a programmable spatial light modulator instead of a specially designed waveguide to produce the required dispersion profile. Additionally, the researchers claim that the energy of the quartic laser beam pulses is regarded as proportional to τ−3, as predicted for fourth-order dispersion solitons.