new progress! The bottleneck of infrared ultrafast mode-locked laser is finally broken

However, due to the inherent quantum well structure of the current light source materials (mainly InGaAs), which limits the wavelength range of its operation, most of the ultra-short pulse light sources are concentrated below 3 μm, which limits the wavelength to a large extent. its further applications. To solve this problem, researchers from Shanghai Jiao Tong University designed a SESAM with InAs and GaSb as superlattices, and used the strong coupling between the band gap and the potential well to change the saturable absorption wavelength of the structure to make it work The wavelength is extended to the range of 3~5 μm.

Fig. Schematic diagram of the structure of the novel SESAM and its energy band diagram

Using the designed SESAM, the researchers experimentally found that the Er:ZBLAN fiber laser can achieve long-term stable mode-locking operation at a wavelength of 3.5 μm, which not only proves that the laser can "provide long-term stable MIR ultrashort pulses", but also validates the SESAM reliability. In addition, since this SESAM is a narrow-band pulse generated by quantum wells, it can be applied to fluoride fiber lasers, crystal lasers and even semiconductor lasers in the 3–5 μm spectral range by adjusting the parameters.
The researchers also said: "The designed SESAM has produced many landmark breakthroughs at the laser level, completely changing the development of ultrafast mode-locked lasers." In the future, it can be used in mid-infrared spectroscopy and medical diagnosis. field.