Whispering gallery mode microcavities stand out among other microdevices due to their long photon lifetime and strong light confinement characteristics. In particular, such microcavities made of polymers come up with additional advantages, e.g. ease of processing/shaping and their wide variety of properties. However, the fabrication of polymeric nano/microdevices with the desirable performance remains challenging. In this work, we report laser action in Rhodamine B doped whispering gallery mode microcavities fabricated by femtosecond laser induced two-photon polymerization. The host material is an acrylic based polymeric hollow microcylinder, which is on-chip integrable and exhibits good structural quality and smooth sidewall surfaces (Q-factor of 1x10^5 for undoped microcavities around 1550 nm). Rhodamine B is directly incorporated into the polymeric matrix, which does not affect significantly the optical properties of the dye. As a result of their high surface optical quality and the low absorption of the acrylate polymer around 600 nm, the dye microlasers exhibited lasing threshold at a pump energy as low as 12 nJ for free space pulsed excitation at 532 nm. Such performance was attained for microcavities fabricated in a single step of femtosecond laser writing, which, as far as we know, had not been demonstrated previously. In addition, a comparison analysis of the emission spectra collected from microstructures featuring different geometries was carried out, showing that random lasing effects do not play a role in the measured threshold. This work therefore opens promising avenues to fabricate low threshold dye microlasers, which are appealing for soft photonics applications.
Nathália B. Tomazio, Leonardo De Boni, and Cleber R. Mendonca, "Low threshold dye whispering gallery mode microlasers fabricated by two-photon polymerization (Conference Presentation)," Proc. SPIE 10518, Laser Resonators, Microresonators, and Beam Control XX, 105180K (Presented at SPIE LASE: January 30, 2018; Published: 14 March 2018); https://doi.org/10.1117/12.2283488.5751435912001.
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