Table of Contents
Novel approach to high-energy ultrashort pulses
A team of Swiss researchers successfully generated high-energy ultrashort pulses with single-mode beam quality by applying nonlinear beam cleaning within a multimode laser cavity. Previously, mode-locked fiber lasers with single-mode optical fibers were thought to support only temporal modes.
Advantages and drawbacks of single-mode fiber lasers
Mode-locked single-mode fiber laser systems are considered to be very advantageous. The benefits include high-gain doping, intrinsically single-spatial mode, and compact setups. High-power mode-locked fiber lasers have some disadvantages, such as high nonlinearity because of the compact core size of optical fibers.
Nonlinear beam cleaning in multimode laser systems
A team of researchers from Switzerland presented a novel technique for producing high-energy, ultrashort pulses with single-mode laser beam quality. They develop nonlinear laser beam cleaning in a multimode laser system cavity. The conventional technique generates low-power ultrashort laser oscillators to solve the problem.
Then it is necessary to increase the laser beam power levels by several amplifiers, but the process of external amplification makes the cost and complexity higher. Researchers prefer applying multimode optical fibers (graded-index) in fiber laser systems because of their low modal dispersion and periodic self-focusing of the light inside.
Spatiotemporal mode-locking technique
The researchers claim that it is possible to perform spatial laser beam cleaning, wavelength conversion, and spatiotemporal mode-locking using graded-index multimode optical fibers. The spatiotemporal technique mode-locking is a relatively new one that allows for creating ultrashort pulses by fiber lasers.
The technique produces “a balance between spatial and temporal effects within a multimode laser system cavity, which supports multiple paths to guide light.” A big multimode core leads to a decrease in the cavity nonlinearity; the fiber laser can achieve high pulse energy without external amplification. High-power mode-locked fiber laser systems suffer from a low-quality output laser beam because of multimode fibers.
Results and practical applications
Finally, the researchers tested the developed fiber laser technology and it demonstrated nonlinear beam cleaning in a multimode laser for the first time. The nonlinear laser beam cleaning promotes the creation of high-energy, ultrashort pulses with single-mode beam quality. The fiber laser technology directs a high-quality laser beam when mode-locking is reached.