A Comparison of Absorber Materials Reveals Which Factors Enable Pulse Generation in Mid-IR Fiber Lasers

Mid-IR fiber lasers are considered promising light sources for molecular analysis, environmental monitoring, and medical diagnostics. In this wavelength range, many gases and biomolecules absorb light particularly strongly. This advantage can only be fully used, however, if the lasers are able to generate short, energetic pulses. A key component needed for this – one that has been difficult to realize – is a robust, fiber-integrated saturable absorber capable of reliably initiating pulse formation.

The Junior Research Group “Ultrafast Fiber Lasers” at Leibniz IPHT, led by Dr. Maria Chernysheva, and co-authors have now investigated which material properties determine whether a fiber laser operating around 2.8 micrometers can in fact produce short pulses. The researchers compared two different absorber concepts within the same laser architecture: an aerosol-synthesized carbon nanotube (CNT) film and a GaSb-based semiconductor saturable absorber mirror (SESAM).

Both materials enabled operation in the so-called Q-switched mode-locking regime, representing high freuqncy ultrashort pulse sequence with slower varying amplitude, indicating that basic pulse formation was achieved. Yet the comparison reveals clear differences. The CNT absorber reliably triggers pulse formation and is well suited for fully fiber-integrated designs, but becomes thermally sensitive at higher pump powers. The GaSbbased SESAM, in contrast, remains stable under increased pumping and produces shorter, more energetic pulses—though it is considerably more complex to fabricate and less flexible to tune.

“We show that an aerosol-synthesized CNT film can indeed support Q-switched mode-locking in the mid-infrared,” says Maria Chernysheva. “This opens new possibilities for compact, fiber-based laser sources and highlights how strongly pulse dynamics depend on the absorber’s material properties.”

“By comparing both approaches directly, we gain a clearer understanding on pathways to optimising the parameters of the absorbers for achieving reliable short-pulse generation in mid-IR fiber lasers,” adds first author Boris Perminov. “This is crucial for making Mid-IR ultrafast fibre lasers simpler and more stable in the future.”

Original publication: https://doi.org/10.1002/adpr.202500065