More recently, SAs based on two-dimensional materials like nickel oxide (NiO) and zinc oxide (ZnO) have been widely deployed in Q-switched and mode-locked pulse generation. While showing some good optical properties, the performance of some of these SAs is limited by a low damage threshold and low output power. Henna (Lawsonia inermis) is one of the most popular natural dyes and its color ranges from light to dark brown. Its dye is easy to extract from its plant leaves and is soluble in water and alcohol. It has a wide absorbance range and acts as an anti-corrosion in various metallic mediums. Thus, it has a good potential to become a SA as it has a large optical nonlinearity and better stability than other materials.
Passive Q-switching operation was realized using a lawsone (2-hydroxy-1,4-naphthoquinone) thin film as a SA. These laser-generated pulses train with a maximum repetition rate of 80 kHz. This paper demonstrates a passively mode-locked EDFL utilizing the lawsone SA, which shows a nonlinear optical response with a modulation depth or saturable absorption of 12%.
The Lawsone SA was made by embedding the Lawsone molecules into polyvinyl alcohol (PVA) utilizing a liquid phase exfoliation method. These images were scanned at a low and high accelerating voltage The low-magnification image shows the dispersion of the Lawsone dye islands along the PVA surface. These islands’ dispersion causes non-uniformity on the polymer surface. The energy-dispersive X-ray (EDX) spectroscopy was carried out to determine the elemental composition of the Lawsone PVA thin film. The optical absorbance intensity of the Lawsone PVA thin film is higher than that of the pure PVA thin film.
The nonlinear transmission of Lawsone SA was evaluated by using a balanced twin detector technique. The mode-locked pulses were amplified by an erbium-doped fiber amplifier (EDFA), and the EDFA was linked to an optical attenuator that controlled the laser output power. The laser operated at the wavelength of 1567.5 nm and generated stretched pulses at the pump power range of 33.6 mW to 43.3 mW. It produced a mode-locked laser with a fixed repetition rate of 3.4 MHz and a pulse width of 1.47 ps. These results show that it is feasible to produce picosecond mode-locked pulses in the EDFL cavity using Lawsone SA.
Author: Prof. Dr. Retna Apsari, M.Si
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https://www.sciencedirect.com/science/article/pii/S2666950121000948
Rawan S.M. Soboh., Ahmed H.H. Al-Masoodi., Retna Apsari., Fuad. N.A. Erman., Ab. H. H, Al-Masoodi., H.Arof., S.W. Harun. Stretched-pulse generation in all-fiber mode-locked erbium-doped fiber laser using Lawsone dye saturable absorberhttps://doi.org/10.1016/j.rio.2021.100148
