Abstract
The combination of the outstanding properties of whispering gallery modes with both the flexibility and ease of processing of polymers is particularly attractive for photonics applications. However, the versatile fabrication of polymeric nano/microdevices with the desired photonic performance has proven challenging. Here, we report on lasing in Rhodamine B doped whispering gallery mode microcavities fabricated by direct laser writing via two-photon polymerization. Threshold pump energies as low as 12 nJ were achieved for free-space pulsed excitation at 532 nm. To the best of our knowledge, this is the lowest laser threshold attained for microcavities fabricated in a single step of femtosecond laser writing, a remarkable feat that stands out from other fabrication methods.
Highlights
Pioneering studies back in the sixties demonstrated the potential of many dyes as active medium for the development of tunable coherent light sources, covering the spectrum from ultraviolet to infrared wavelengths[1,2,3]
Lasing activity from Rhodamine B (RhB) doped whispering gallery mode microcavities fabricated via two-photon polymerization is reported
Laser action in dye-doped polymeric microcavities fabricated via femtosecond laser induced two-photon polymerization was demonstrated
Summary
Pioneering studies back in the sixties demonstrated the potential of many dyes as active medium for the development of tunable coherent light sources, covering the spectrum from ultraviolet to infrared wavelengths[1,2,3]. The so-called whispering gallery mode (WGM) microcavities stand out Their unique characteristics, such as narrow spectral linewidth, extremely small mode volume and very high power density make them promising tools for the realization of low threshold lasers[6]. Femtosecond laser induced two-photon polymerization (2PP) has been proven to be a powerful tool for high-precision 3D microfabrication of organic materials[15,16,17]. Such technique benefits from the nonlinear nature of the two photon absorption process, which translates into spatial confinement of the photo-driven polymerization[18]. The giant power density achieved within the microcavities, combined with the high fluorescence quantum yield of RhB, gives rise to a lasing threshold as low as 12 nJ for free space pulsed excitation at 532 nm
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